Tag Archives: Visualization

Turbo, An Improved Rainbow Colormap for Visualization



False color maps show up in many applications in computer vision and machine learning, from visualizing depth images to more abstract uses, such as image differencing. Colorizing images helps the human visual system pick out detail, estimate quantitative values, and notice patterns in data in a more intuitive fashion. However, the choice of color map can have a significant impact on a given task. For example, interpretation of “rainbow maps” have been linked to lower accuracy in mission critical applications, such as medical imaging. Still, in many applications, “rainbow maps” are preferred since they show more detail (at the expense of accuracy) and allow for quicker visual assessment.
Left: Disparity image displayed as greyscale. Right: The commonly used Jet rainbow map being used to create a false color image.
One of the most commonly used color mapping algorithms in computer vision applications is Jet, which is high contrast, making it useful for accentuating even weakly distinguished image features. However, if you look at the color map gradient, one can see distinct “bands” of color, most notably in the cyan and yellow regions. This causes sharp transitions when the map is applied to images, which are misleading when the underlying data is actually smoothly varying. Because the rate at which the color changes ‘perceptually’ is not constant, Jet is not perceptually uniform. These effects are even more pronounced for users that are color blind, to the point of making the map ambiguous:
The above image with simulated Protanopia
Today there are many modern alternatives that are uniform and color blind accessible, such as Viridis or Inferno from matplotlib. While these linear lightness maps solve many important issues with Jet, their constraints may make them suboptimal for day to day tasks where the requirements are not as stringent.
ViridisInferno
Today we are happy to introduce Turbo, a new colormap that has the desirable properties of Jet while also addressing some of its shortcomings, such as false detail, banding and color blindness ambiguity. Turbo was hand-crafted and fine-tuned to be effective for a variety of visualization tasks. You can find the color map data and usage instructions for Python here and C/C++ here, as well as a polynomial approximation here.

Development
To create the Turbo color map, we created a simple interface that allowed us to interactively adjust the sRGB curves using a 7-knot cubic spline, while comparing the result on a selection of sample images as well as other well known color maps.
Screenshot of the interface used to create and tune Turbo.
This approach provides control while keeping the curve C2 continuous. The resulting color map is not “perceptually linear” in the quantitative sense, but it is more smooth than Jet, without introducing false detail.

Turbo
Jet
Comparison with Common Color Maps
Viridis is a linear color map that is generally recommended when false color is needed because it is pleasant to the eye and it fixes most issues with Jet. Inferno has the same linear properties of Viridis, but is higher contrast, making it better for picking out detail. However, some feel that it can be harsh on the eyes. While this isn’t a concern for publishing, it does affect people’s choice when they must spend extended periods examining visualizations.
TurboJet
ViridisInferno
Because of rapid color and lightness changes, Jet accentuates detail in the background that is less apparent with Viridis and even Inferno. Depending on the data, some detail may be lost entirely to the naked eye. The background in the following images is barely distinguishable with Inferno (which is already punchier than Viridis), but clear with Turbo.
InfernoTurbo
Turbo mimics the lightness profile of Jet, going from low to high back down to low, without banding. As such, its lightness slope is generally double that of Viridis, allowing subtle changes to be more easily seen. This is a valuable feature, since it greatly enhances detail when color can be used to disambiguate the low and high ends.
TurboJet
ViridisInferno
Lightness plots generated by converting the sRGB values to CIECAM02-UCS and displaying the lightness value (J) in greyscale. The black line traces the lightness value from the low end of the color map (left) to the high end (right).
The Viridis and Inferno plots are linear, with Inferno exhibiting a higher slope and over a broader range. Jet’s plot is erratic and peaky, and banding can be seen clearly even in the grayscale image. Turbo has a similar asymmetric profile to Jet with the lows darker than the highs.This is intentional, to make cases where low values appear next to high values more distinct. The curvature in the lower region is also different from the higher region, due to the way blues are perceived in comparison to reds.

Although this low-high-low curve increases detail, it comes at the cost of lightness ambiguity. When rendered in grayscale, the coloration will be ambiguous, since some of the lower values will look identical to higher values. Consequently, Turbo is inappropriate for grayscale printing and for people with the rare case of achromatopsia.

Semantic Layers
When examining disparity maps, it is often desirable to compare values on different sides of the image at a glance. This task is much easier when values can be mentally mapped to a distinct semantic color, such as red or blue. Thus, having more colors helps the estimation ease and accuracy.
TurboJet
ViridisInferno
With Jet and Turbo, it’s easy to see which objects on the left of the frame are at the same depth as objects on the right, even though there is a visual gap in the middle. For example, you can easily spot which sphere on the left is at the same depth as the ring on the right. This is much harder to determine using Viridis or Inferno, which have far fewer distinct colors. Compared to Jet, Turbo is also much more smooth and has no “false layers” due to banding. You can see this improvement more clearly if the incoming values are quantized:
Left: Quantized Turbo colormap. Up to 33 quantized colors remain distinguishable and smooth in both lightness and hue change. Right: Quantized Jet color map. Many neighboring colors appear the same; Yellow and Cyan colors appear brighter than the rest.
Quick Judging
When doing a quick comparison of two images, it’s much easier to judge the differences in color than in lightness (because our attention system prioritizes hue). For example, imagine we have an output image from a depth estimation algorithm beside the ground truth. With Turbo it’s easy to discern whether or not the two are in agreement and which regions may disagree.
“Output” Viridis“Ground Truth” Viridis
“Output” Turbo“Ground Truth” Turbo
In addition, it is easy to estimate quantitative values, since they map to distinguishable and memorable colors.
Diverging Map Use Cases
Although the Turbo color map was designed for sequential use (i.e., values [0-1]), it can be used as a diverging colormap as well, as is needed in difference images, for example. When used this way, zero is green, negative values are shades of blue, and positive values are shades of red. Note, however, that the negative minimum is darker than the positive maximum, so it is not truly balanced.
"Ground Truth" disparity imageEstimated disparity image
Difference Image (ground truth - estimated disparity image), visualized with Turbo
Accessibility for Color Blindness
We tested Turbo using a color blindness simulator and found that for all conditions except Achromatopsia (total color blindness), the map remains distinguishable and smooth. In the case of Achromatopsia, the low and high ends are ambiguous. Since the condition affects 1 in 30,000 individuals (or 0.00003%), Turbo should be usable by 99.997% of the population.
Test Image
ProtanomalyProtanopia
DeuteranomalyDeuteranopia
TritanomalyTritanopia
Blue cone monochromacyAchromatopsia
Conclusion
Turbo is a slot-in replacement for Jet, and is intended for day-to-day tasks where perceptual uniformity is not critical, but one still wants a high contrast, smooth visualization of the underlying data. It can be used as a sequential as well as a diverging map, making it a good all-around map to have in the toolbox. You can find the color map data and usage instructions for Python here and for C/C++ here. There is also a polynomial approximation here, for cases where a look-up table may not be desirable.Our team uses it for visualizing disparity maps, error maps, and various other scalar quantities, and we hope you’ll find it useful as well.

Acknowledgements
Ambrus Csaszar stared at many color ramps with me in order to pick the right tradeoffs between uniformity and detail accentuation. Christian Haene integrated the map into our team’s tools, which caused wide usage and thus spurred further improvements. Matthias Kramm and Ruofei Du came up with closed form approximations.

Source: Google AI Blog


An Interactive, Automated 3D Reconstruction of a Fly Brain



The goal of connectomics research is to map the brain’s "wiring diagram" in order to understand how the nervous system works. A primary target of recent work is the brain of the fruit fly (Drosophila melanogaster), which is a well-established research animal in biology. Eight Nobel Prizes have been awarded for fruit fly research that has led to advances in molecular biology, genetics, and neuroscience. An important advantage of flies is their size: Drosophila brains are relatively small (one hundred thousand neurons) compared to, for example, a mouse brain (one hundred million neurons) or a human brain (one hundred billion neurons). This makes fly brains easier to study as a complete circuit.

Today, in collaboration with the Howard Hughes Medical Institute (HHMI) Janelia Research Campus and Cambridge University, we are excited to publish “Automated Reconstruction of a Serial-Section EM Drosophila Brain with Flood-Filling Networks and Local Realignment”, a new research paper that presents the automated reconstruction of an entire fruit fly brain. We are also making the full results available for anyone to download or to browse online using an interactive, 3D interface we developed called Neuroglancer.
A 40-trillion pixel fly brain reconstruction, open to anyone for interactive viewing. Bottom right: smaller datasets that Google AI analyzed in publications in 2016 and 2018.
Automated Reconstruction of 40 Trillion Pixels
Our collaborators at HHMI sectioned a fly brain into thousands of ultra-thin 40-nanometer slices, imaged each slice using a transmission electron microscope (resulting in over forty trillion pixels of brain imagery), and then aligned the 2D images into a coherent, 3D image volume of the entire fly brain. Using thousands of Cloud TPUs we then applied Flood-Filling Networks (FFNs), which automatically traced each individual neuron in the fly brain.

While the algorithm generally performed well, we found performance degraded when the alignment was imperfect (image content in consecutive sections was not stable) or when occasionally there were multiple consecutive slices missing due to difficulties associated with the sectioning and imaging process. In order to compensate for these issues we combined FFNs with two new procedures. First, we estimated the slice-to-slice consistency everywhere in the 3D image and then locally stabilized the image content as the FFN traced each neuron. Second, we used a “Segmentation-Enhanced CycleGAN” (SECGAN) to computationally “hallucinate” missing slices in the image volume. SECGANs are a type of generative adversarial network specialized for image segmentation. We found that the FFN was able to trace through locations with multiple missing slices much more robustly when using the SECGAN-hallucinated image data.
Interactive Visualization of the Fly Brain with Neuroglancer
When working with 3D images that contain trillions of pixels and objects with complicated shapes, visualization is both essential and difficult. Inspired by Google’s history of developing new visualization technologies, we designed a new tool that was scalable and powerful, but also accessible to anybody with a web browser that supports WebGL. The result is Neuroglancer, an open-source project (github) that enables viewing of petabyte-scale 3D volumes, and supports many advanced features such as arbitrary-axis cross-sectional reslicing, multi-resolution meshes, and the powerful ability to develop custom analysis workflows via integration with Python. This tool has become heavily used by collaborators at the Allen Institute for Brain Science, Harvard University, HHMI, Max Planck Institute, MIT, Princeton University, and elsewhere.
A recorded demonstration of Neuroglancer. Interactive version available here.
Next Steps
Our collaborators at HHMI and Cambridge University have already begun using this reconstruction to accelerate their studies of learning, memory, and perception in the fly brain. However, the results described above are not yet a true connectome since establishing a connectome requires the identification of synapses. We are working closely with the FlyEM team at Janelia Research Campus to create a highly verified and exhaustive connectome of the fly brain using images acquired with “FIB-SEM” technology.

Acknowledgements
We would like to acknowledge core contributions from Tim Blakely, Viren Jain, Michal Januszewski, Laramie Leavitt, Larry Lindsey, Mike Tyka (Google), as well as Alex Bates, Davi Bock, Greg Jefferis, Feng Li, Mathew Nichols, Eric Perlman, Istvan Taisz, and Zhihao Zheng (Cambridge University, HHMI Janelia, Johns Hopkins University, and University of Vermont).

Source: Google AI Blog


Exploring Neural Networks with Activation Atlases



Neural networks have become the de facto standard for image-related tasks in computing, currently being deployed in a multitude of scenarios, ranging from automatically tagging photos in your image library to autonomous driving systems. These machine-learned systems have become ubiquitous because they perform more accurately than any system humans were able to directly design without machine learning. But because essential details of these systems are learned during the automated training process, understanding how a network goes about its given task can sometimes remain a bit of a mystery.

Today, in collaboration with colleagues at OpenAI, we're publishing "Exploring Neural Networks with Activation Atlases", which describes a new technique aimed at helping to answer the question of what image classification neural networks "see" when provided an image. Activation atlases provide a new way to peer into convolutional vision networks, giving a global, hierarchical, and human-interpretable overview of concepts within the hidden layers of a network. We think of activation atlases as revealing a machine-learned alphabet for images — an array of simple, atomic concepts that are combined and recombined to form much more complex visual ideas. We are also releasing some jupyter notebooks to help you get you started in making your own activation atlases.

A detail view of an activation atlas from one of the layers of the InceptionV1 vision classification network. It reveals many of the visual detectors that the network uses to classify images, such as different types of fruit-like textures, honeycomb patterns and fabric-like textures.
The activation atlases shown below are built from a convolutional image classification network, Inceptionv1, that was trained on the ImageNet dataset. In general, classification networks are shown an image and then asked to give that image a label from one of 1,000 predetermined classes — such as "carbonara", "snorkel" or "frying pan". To do this, our network evaluates the image data progressively through about ten layers, each made of hundreds of neurons that each activate to varying degrees on different types of image patches. One neuron at one layer might respond positively to a dog's ear, another at an earlier layer might respond to a high-contrast vertical line.

An activation atlas is built by collecting the internal activations from each of these layers of our neural network from one million images. These activations, represented by a complex set of high-dimensional vectors, is projected into useful 2D layouts via UMAP, a dimensionality-reduction technique that preserving some of the local structure of the original high-dimensional space.

This takes care of organizing our activation vectors, but we also need to aggregate them into a more manageable number — all the activations are too many to consume at a glance. To do this, we draw a grid over the 2D layout we created. For each cell in our grid, we average all the activations that lie within the boundaries of that cell, and use feature visualization to create an iconic representation.
Left: A randomized set of one million images is fed through the network, collecting one random spatial activation per image. Center: The activations are fed through UMAP to reduce them to two dimensions. They are then plotted, with similar activations placed near each other. Right: We then draw a grid, average the activations that fall within a cell, and run feature inversion on the averaged activation.
Below we can see an activation atlas for just one layer in a neural network (remember that these classification models can have half a dozen or more layers). It reveals a universe of the visual concepts the network has learned to classify images at this layer. This atlas can be a bit overwhelming at first glance — there's a lot going on! This diversity is a reflection of the variety of visual abstractions and concepts the model has developed.
An overview of an activation atlas for one of the many layers (mixed4c) within Inception v1. It is about halfway through the network.
In this detail, we can see detectors for different types of leaves and plants.
Here we can see different detectors for water, lakes and sandbars.
Here we see different types of buildings and bridges.
As we mentioned before, there are many more layers in this network. Let's look at the layers that came before this one to see how these concepts become more refined as we go deeper into the network (Each layer builds its activations on top of the preceding layer's activations).
In an early layer, mixed4a, there is a vague "mammalian" area.
By the next layer in the network, mixed4b, animals and people have been disentangled, with some fruit and food emerging in the middle.
By layer mixed4c these concepts are further refined and differentiated into small "peninsulas".
Here we've seen the global structure evolve from layer to layer, but each of the individual concepts also become more specific and complex from layer to layer. If we focus on the areas of three layers that contribute to a specific classification, say "cabbage", we can see this clearly.
Left: This early layer is very nonspecific in comparison to the others. Center: By the middle layer, the images definitely resemble leaves, but they could be any type of plant. Right: By the last layer the images are very specific to cabbage, leaves curved into rounded balls.
There is another phenomenon worth noting: not only are concepts being refined as you move from layer to layer, but new concepts seem to be appearing out of combinations of old ones.
You can see how sand and water are distinct concepts in a middle layer, mixed4c (left and center), both with strong attributions to the classification of "sandbar". Contrast this with a later layer (right), mixed5b, where the two ideas seem to be fused into one activation.
Instead of zooming in on certain areas of the whole atlas for a specific layer, we can also create an atlas at a specific layer for just one of the 1,000 classes in ImageNet. This will show the concepts and detectors that the network most often uses to classify a specific class, say "red fox" for instance.
Here we can more clearly see what the network is focusing on to classify a "red fox". There are pointy ears, white snouts surrounded by red fur, and wooded or snowy backgrounds.
Here we can see the many different scales and angles of detectors for "tile roof".
For "ibex", we see detectors for horns and brown fur, but also environments where we might find such animals, like rocky hillsides.
Like the detectors for tile roof, "artichoke" also has many different sizes of detectors for the texture of an artichoke, but we also get some purple flower detectors. These are presumably detecting the blossoms of an artichoke plant.
These atlases not only reveal nuanced visual abstractions within a model, but they can also reveal high-level misunderstandings. For example, by looking at an activation atlas for a "great white shark" we water and triangular fins (as expected) but we also see something that looks like a baseball. This hints at a shortcut taken by this research model where it conflates the red baseball stitching with the open mouth of a great white shark.
We can test this by using a patch of an image of a baseball to switch the model's classification of a particular image from "grey whale" to "great white shark".
We hope that activation atlases will be a useful tool in the quiver of techniques that are making machine learning more accessible and interpretable. To help you get started, we've released several jupyter notebooks which can be executed immediately in your browser with one click via colab. They build upon the previously released toolkit Lucid, which includes code for many other interpretability visualization techniques included as well. We're excited to see what you discover!

Source: Google AI Blog


Exploring Neural Networks with Activation Atlases



Neural networks have become the de facto standard for image-related tasks in computing, currently being deployed in a multitude of scenarios, ranging from automatically tagging photos in your image library to autonomous driving systems. These machine-learned systems have become ubiquitous because they perform more accurately than any system humans were able to directly design without machine learning. But because essential details of these systems are learned during the automated training process, understanding how a network goes about its given task can sometimes remain a bit of a mystery.

Today, in collaboration with colleagues at OpenAI, we're publishing "Exploring Neural Networks with Activation Atlases", which describes a new technique aimed at helping to answer the question of what image classification neural networks "see" when provided an image. Activation atlases provide a new way to peer into convolutional vision networks, giving a global, hierarchical, and human-interpretable overview of concepts within the hidden layers of a network. We think of activation atlases as revealing a machine-learned alphabet for images — an array of simple, atomic concepts that are combined and recombined to form much more complex visual ideas. We are also releasing some jupyter notebooks to help you get you started in making your own activation atlases.

A detail view of an activation atlas from one of the layers of the InceptionV1 vision classification network. It reveals many of the visual detectors that the network uses to classify images, such as different types of fruit-like textures, honeycomb patterns and fabric-like textures.
The activation atlases shown below are built from a convolutional image classification network, Inceptionv1, that was trained on the ImageNet dataset. In general, classification networks are shown an image and then asked to give that image a label from one of 1,000 predetermined classes — such as "carbonara", "snorkel" or "frying pan". To do this, our network evaluates the image data progressively through about ten layers, each made of hundreds of neurons that each activate to varying degrees on different types of image patches. One neuron at one layer might respond positively to a dog's ear, another at an earlier layer might respond to a high-contrast vertical line.

An activation atlas is built by collecting the internal activations from each of these layers of our neural network from one million images. These activations, represented by a complex set of high-dimensional vectors, is projected into useful 2D layouts via UMAP, a dimensionality-reduction technique that preserving some of the local structure of the original high-dimensional space.

This takes care of organizing our activation vectors, but we also need to aggregate them into a more manageable number — all the activations are too many to consume at a glance. To do this, we draw a grid over the 2D layout we created. For each cell in our grid, we average all the activations that lie within the boundaries of that cell, and use feature visualization to create an iconic representation.
Left: A randomized set of one million images is fed through the network, collecting one random spatial activation per image. Center: The activations are fed through UMAP to reduce them to two dimensions. They are then plotted, with similar activations placed near each other. Right: We then draw a grid, average the activations that fall within a cell, and run feature inversion on the averaged activation.
Below we can see an activation atlas for just one layer in a neural network (remember that these classification models can have half a dozen or more layers). It reveals a universe of the visual concepts the network has learned to classify images at this layer. This atlas can be a bit overwhelming at first glance — there's a lot going on! This diversity is a reflection of the variety of visual abstractions and concepts the model has developed.
An overview of an activation atlas for one of the many layers (mixed4c) within Inception v1. It is about halfway through the network.
In this detail, we can see detectors for different types of leaves and plants.
Here we can see different detectors for water, lakes and sandbars.
Here we see different types of buildings and bridges.
As we mentioned before, there are many more layers in this network. Let's look at the layers that came before this one to see how these concepts become more refined as we go deeper into the network (Each layer builds its activations on top of the preceding layer's activations).
In an early layer, mixed4a, there is a vague "mammalian" area.
By the next layer in the network, mixed4b, animals and people have been disentangled, with some fruit and food emerging in the middle.
By layer mixed4c these concepts are further refined and differentiated into small "peninsulas".
Here we've seen the global structure evolve from layer to layer, but each of the individual concepts also become more specific and complex from layer to layer. If we focus on the areas of three layers that contribute to a specific classification, say "cabbage", we can see this clearly.
Left: This early layer is very nonspecific in comparison to the others. Center: By the middle layer, the images definitely resemble leaves, but they could be any type of plant. Right: By the last layer the images are very specific to cabbage, leaves curved into rounded balls.
There is another phenomenon worth noting: not only are concepts being refined as you move from layer to layer, but new concepts seem to be appearing out of combinations of old ones.
You can see how sand and water are distinct concepts in a middle layer, mixed4c (left and center), both with strong attributions to the classification of "sandbar". Contrast this with a later layer (right), mixed5b, where the two ideas seem to be fused into one activation.
Instead of zooming in on certain areas of the whole atlas for a specific layer, we can also create an atlas at a specific layer for just one of the 1,000 classes in ImageNet. This will show the concepts and detectors that the network most often uses to classify a specific class, say "red fox" for instance.
Here we can more clearly see what the network is focusing on to classify a "red fox". There are pointy ears, white snouts surrounded by red fur, and wooded or snowy backgrounds.
Here we can see the many different scales and angles of detectors for "tile roof".
For "ibex", we see detectors for horns and brown fur, but also environments where we might find such animals, like rocky hillsides.
Like the detectors for tile roof, "artichoke" also has many different sizes of detectors for the texture of an artichoke, but we also get some purple flower detectors. These are presumably detecting the blossoms of an artichoke plant.
These atlases not only reveal nuanced visual abstractions within a model, but they can also reveal high-level misunderstandings. For example, by looking at an activation atlas for a "great white shark" we water and triangular fins (as expected) but we also see something that looks like a baseball. This hints at a shortcut taken by this research model where it conflates the red baseball stitching with the open mouth of a great white shark.
We can test this by using a patch of an image of a baseball to switch the model's classification of a particular image from "grey whale" to "great white shark".
We hope that activation atlases will be a useful tool in the quiver of techniques that are making machine learning more accessible and interpretable. To help you get started, we've released several jupyter notebooks which can be executed immediately in your browser with one click via colab. They build upon the previously released toolkit Lucid, which includes code for many other interpretability visualization techniques included as well. We're excited to see what you discover!

Source: Google AI Blog


The What-If Tool: Code-Free Probing of Machine Learning Models



Building effective machine learning (ML) systems means asking a lot of questions. It's not enough to train a model and walk away. Instead, good practitioners act as detectives, probing to understand their model better: How would changes to a datapoint affect my model’s prediction? Does it perform differently for various groups–for example, historically marginalized people? How diverse is the dataset I am testing my model on?

Answering these kinds of questions isn’t easy. Probing “what if” scenarios often means writing custom, one-off code to analyze a specific model. Not only is this process inefficient, it makes it hard for non-programmers to participate in the process of shaping and improving ML models. One focus of the Google AI PAIR initiative is making it easier for a broad set of people to examine, evaluate, and debug ML systems.

Today, we are launching the What-If Tool, a new feature of the open-source TensorBoard web application, which let users analyze an ML model without writing code. Given pointers to a TensorFlow model and a dataset, the What-If Tool offers an interactive visual interface for exploring model results.
The What-If Tool, showing a set of 250 face pictures and their results from a model that detects smiles.
The What-If Tool has a large set of features, including visualizing your dataset automatically using Facets, the ability to manually edit examples from your dataset and see the effect of those changes, and automatic generation of partial dependence plots which show how the model’s predictions change as any single feature is changed. Let’s explore two features in more detail.
Exploring what-if scenarios on a datapoint.
Counterfactuals
With a click of a button you can compare a datapoint to the most similar point where your model predicts a different result. We call such points "counterfactuals," and they can shed light on the decision boundaries of your model. Or, you can edit a datapoint by hand and explore how the model’s prediction changes. In the screenshot below, the tool is being used on a binary classification model that predicts whether a person earns more than $50k based on public census data from the UCI census dataset. This is a benchmark prediction task used by ML researchers, especially when analyzing algorithmic fairness — a topic we'll get to soon. In this case, for the selected datapoint, the model predicted with 73% confidence that the person earns more than $50k. The tool has automatically located the most-similar person in the dataset for which the model predicted earnings of less than $50k and compares the two side-by-side. In this case, with just a minor difference in age and an occupation change, the model’s prediction has flipped.
Comparing counterfactuals.
Analysis of Performance and Algorithmic Fairness
You can also explore the effects of different classification thresholds, taking into account constraints such as different numerical fairness criteria. The below screenshot shows the results of a smile detector model, trained on the open-source CelebA dataset which consists of annotated face images of celebrities. Below, the faces in the dataset are divided by whether they have brown hair, and for each of the two groups there is an ROC curve and confusion matrix of the predictions, along with sliders for setting how confident the model must be before determining that a face is smiling. In this case, the confidence thresholds for the two groups were set automatically by the tool to optimize for equal opportunity.
Comparing the performance of two slices of data on a smile detection model, with their classification thresholds set to satisfy the “equal opportunity” constraint.
Demos
To illustrate the capabilities of the What-If Tool, we’ve released a set of demos using pre-trained models:
  • Detecting misclassifications: A multiclass classification model, which predicts plant type from four measurements of a flower from the plant. The tool is helpful in showing the decision boundary of the model and what causes misclassifications. This model is trained with the UCI iris dataset.
  • Assessing fairness in binary classification models: The image classification model for smile detection mentioned above. The tool is helpful in assessing algorithmic fairness across different subgroups. The model was purposefully trained without providing any examples from a specific subset of the population, in order to show how the tool can help uncover such biases in models. Assessing fairness requires careful consideration of the overall context — but this is a useful quantitative starting point.
  • Investigating model performance across different subgroups: A regression model that predicts a subject’s age from census information. The tool is helpful in showing relative performance of the model across subgroups and how the different features individually affect the prediction. This model is trained with the UCI census dataset.
What-If in Practice
We tested the What-If Tool with teams inside Google and saw the immediate value of such a tool. One team quickly found that their model was incorrectly ignoring an entire feature of their dataset, leading them to fix a previously-undiscovered code bug. Another team used it to visually organize their examples from best to worst performance, leading them to discover patterns about the types of examples their model was underperforming on.

We look forward to people inside and outside of Google using this tool to better understand ML models and to begin assessing fairness. And as the code is open-source, we welcome contributions to the tool.

Acknowledgments
The What-If Tool was a collaborative effort, with UX design by Mahima Pushkarna, Facets updates by Jimbo Wilson, and input from many others. We would like to thank the Google teams that piloted the tool and provided valuable feedback and the TensorBoard team for all their help.

Source: Google AI Blog


Realtime tSNE Visualizations with TensorFlow.js



In recent years, the t-distributed Stochastic Neighbor Embedding (tSNE) algorithm has become one of the most used and insightful techniques for exploratory data analysis of high-dimensional data. Used to interpret deep neural network outputs in tools such as the TensorFlow Embedding Projector and TensorBoard, a powerful feature of tSNE is that it reveals clusters of high-dimensional data points at different scales while requiring only minimal tuning of its parameters. Despite these advantages, the computational complexity of the tSNE algorithm limits its application to relatively small datasets. While several evolutions of tSNE have been developed to address this issue (mainly focusing on the scalability of the similarity computations between data points), they have so far not been enough to provide a truly interactive experience when visualizing the evolution of the tSNE embedding for large datasets.

In “Linear tSNE Optimization for the Web”, we present a novel approach to tSNE that heavily relies on modern graphics hardware. Given the linear complexity of the new approach, our method generates embeddings faster than comparable techniques and can even be executed on the client side in a web browser by leveraging GPU capabilities through WebGL. The combination of these two factors allows for real-time interactive visualization of large, high-dimensional datasets. Furthermore, we are releasing this work as an open source library in the TensorFlow.js family in the hopes that the broader research community finds it useful.
Real-time evolution of the tSNE embedding for the complete MNIST dataset with our technique. The dataset contains images of 60,000 handwritten digits. You can find a live demo here.
The aim of tSNE is to cluster small “neighborhoods” of similar data points while also reducing the overall dimensionality of the data so it is more easily visualized. In other words, the tSNE objective function measures how well these neighborhoods of similar data are preserved in the 2 or 3-dimensional space, and arranges them into clusters accordingly.

In previous work, the minimization of the tSNE objective was performed as a N-body simulation problem, in which points are randomly placed in the embedding space and two different types of forces are applied on each point. Attractive forces bring the points closer to the points that are most similar in the high-dimensional space, while repulsive forces push them away from all the neighbors in the embedding.

While the attractive forces are acting on a small subset of points (i.e., similar neighbors), repulsive forces are in effect from all pairs of points. Due to this, tSNE requires significant computation and many iterations of the objective function, which limits the possible dataset size to just a few hundred data points. To improve over a brute force solution, the Barnes-Hut algorithm was used to approximate the repulsive forces and the gradient of the objective function. This allows scaling of the computation to tens of thousand data points, but it requires more than 15 minutes to compute the MNIST embedding in a C++ implementation.

In our paper, we propose a solution to this scaling problem by approximating the gradient of the objective function using textures that are generated in WebGL. Our technique draws a “repulsive field” at every minimization iteration using a three channel texture, with the 3 components treated as colors and drawn in the RGB channels. The repulsive field is obtained for every point to represent both the horizontal and vertical repulsive force created by the point, and a third component used for normalization. Intuitively, the normalization term ensures that the magnitude of the shifts matches the similarity measure in the high-dimensional space. In addition, the resolution of the texture is adaptively changed to keep the number of pixels drawn constant.
Rendering of the three functions used to approximate the repulsive effect created by a single point. In the above figure the repulsive forces show a point in a blue area is pushed to the left/bottom, while a point in the red area is pushed to the right/top while a point in the white region will not move.
The contribution of every point is then added on the GPU, resulting in a texture similar to those presented in the GIF below, that approximate the repulsive fields. This innovative repulsive field approach turns out to be much more GPU friendly than more commonly used calculation of point-to-point interactions. This is because repulsion for multiple points can be computed at once and in a very fast way in the GPU. In addition, we implemented the computation of the attraction between points in the GPU.
This animation shows the evolution of the tSNE embedding (upper left) and of the scalar fields used to approximate its gradient with normalization term (upper right), horizontal shift (bottom left) and vertical shift (bottom right).
We additionally revised the update of the embedding from an ad-hoc implementation to a series of standard tensor operations that are computed in TensorFlow.js, a JavaScript library to perform tensor computations in the web browser. Our approach, which is released as an open source library in the TensorFlow.js family, allows us to compute the evolution of the tSNE embedding entirely on the GPU while having better computational complexity.

With this implementation, what used to take 15 minutes to calculate (on the MNIST dataset) can now be visualized in real-time and in the web browser. Furthermore this allows real-time visualizations of much larger datasets, a feature that is particularly useful when deep neural output is analyzed. One main limitation of our work is that this technique currently only works for 2D embeddings. However, 2D visualizations are often preferred over 3D ones as they require more interaction to effectively understand cluster results.

Future Work
We believe that having a fast and interactive tSNE implementation that runs in the browser will empower developers of data analytics systems. We are particularly interested in exploring how our implementation can be used for the interpretation of deep neural networks. Additionally, our implementation shows how lateral thinking in using GPU computations (approximating the gradient using RGB texture) can be used to significantly speed up algorithmic computations. In the future we will be exploring how this kind of gradient approximation can be applied not only to speed-up other dimensionality reduction algorithms, but also to implement other N-body simulations in the web browser using TensorFlow.js.

Acknowledgements
We would like to thank Alexander Mordvintsev, Yannick Assogba, Matt Sharifi, Anna Vilanova, Elmar Eisemann, Nikhil Thorat, Daniel Smilkov, Martin Wattenberg, Fernanda Viegas, Alessio Bazzica, Boudewijn Lelieveldt, Thomas Höllt, Baldur van Lew, Julian Thijssen and Marvin Ritter.

Source: Google AI Blog


The Building Blocks of Interpretability



(Crossposted on the Google Open Source Blog)

In 2015, our early attempts to visualize how neural networks understand images led to psychedelic images. Soon after, we open sourced our code as DeepDream and it grew into a small art movement producing all sorts of amazing things. But we also continued the original line of research behind DeepDream, trying to address one of the most exciting questions in Deep Learning: how do neural networks do what they do?

Last year in the online journal Distill, we demonstrated how those same techniques could show what individual neurons in a network do, rather than just what is “interesting to the network” as in DeepDream. This allowed us to see how neurons in the middle of the network are detectors for all sorts of things — buttons, patches of cloth, buildings — and see how those build up to be more and more sophisticated over the networks layers.
Visualizations of neurons in GoogLeNet. Neurons in higher layers represent higher level ideas.
While visualizing neurons is exciting, our work last year was missing something important: how do these neurons actually connect to what the network does in practice?

Today, we’re excited to publish “The Building Blocks of Interpretability,” a new Distill article exploring how feature visualization can combine together with other interpretability techniques to understand aspects of how networks make decisions. We show that these combinations can allow us to sort of “stand in the middle of a neural network” and see some of the decisions being made at that point, and how they influence the final output. For example, we can see things like how a network detects a floppy ear, and then that increases the probability it gives to the image being a “Labrador retriever” or “beagle”.

We explore techniques for understanding which neurons fire in the network. Normally, if we ask which neurons fire, we get something meaningless like “neuron 538 fired a little bit,” which isn’t very helpful even to experts. Our techniques make things more meaningful to humans by attaching visualizations to each neuron, so we can see things like “the floppy ear detector fired”. It’s almost a kind of MRI for neural networks.
We can also zoom out and show how the entire image was “perceived” at different layers. This allows us to really see the transition from the network detecting very simple combinations of edges, to rich textures and 3d structure, to high-level structures like ears, snouts, heads and legs.
These insights are exciting by themselves, but they become even more exciting when we can relate them to the final decision the network makes. So not only can we see that the network detected a floppy ear, but we can also see how that increases the probability of the image being a labrador retriever.
In addition to our paper, we’re also releasing Lucid, a neural network visualization library building off our work on DeepDream. It allows you to make the sort lucid feature visualizations we see above, in addition to more artistic DeepDream images.

We’re also releasing colab notebooks. These notebooks make it extremely easy to use Lucid to reproduce visualizations in our article! Just open the notebook, click a button to run code — no setup required!
In colab notebooks you can click a button to run code, and see the result below.
This work only scratches the surface of the kind of interfaces that we think it’s possible to build for understanding neural networks. We’re excited to see what the community will do — and we’re excited to work together towards deeper human understanding of neural networks.

Feature Visualization



Have you ever wondered what goes on inside neural networks? Feature visualization is a powerful tool for digging into neural networks and seeing how they work.

Our new article, published in Distill, does a deep exploration of feature visualization, introducing a few new tricks along the way!

Building on our work in DeepDream, and lots of work by others since, we are able to visualize what every neuron a strong vision model (GoogLeNet [1]) detects. Over the course of multiple layers, it gradually builds up abstractions: first it detects edges, then it uses those edges to detect textures, the textures to detect patterns, and the patterns to detect parts of objects….
But neurons don’t understand the world by themselves — they work together. So we also need to understand how they interact with each other. One approach is to explore interpolations between them. What images can make them both fire, to different extents?

Here we interpolate from a neuron that seems to detect artistic patterns to a neuron that seems to detect lizard eyes:
We can also let you try adding different pairs of neurons together, to explore the possibilities for yourself:
In addition to allowing you to play around with visualizations, we explore a variety of techniques for getting feature visualization to work, and let you experiment with using them.
Techniques for visualizing and understanding neural networks are becoming more powerful. We hope our article will help other researchers apply these techniques, and give people a sense of their potential. Check it out on Distill.

Acknowledgement
We're extremely grateful to our co-author, Ludwig Schurbert, who made incredible contributions to our paper and especially to the interactive visualizations.







Build your own Machine Learning Visualizations with the new TensorBoard API



When we open-sourced TensorFlow in 2015, it included TensorBoard, a suite of visualizations for inspecting and understanding your TensorFlow models and runs. Tensorboard included a small, predetermined set of visualizations that are generic and applicable to nearly all deep learning applications such as observing how loss changes over time or exploring clusters in high-dimensional spaces. However, in the absence of reusable APIs, adding new visualizations to TensorBoard was prohibitively difficult for anyone outside of the TensorFlow team, leaving out a long tail of potentially creative, beautiful and useful visualizations that could be built by the research community.

To allow the creation of new and useful visualizations, we announce the release of a consistent set of APIs that allows developers to add custom visualization plugins to TensorBoard. We hope that developers use this API to extend TensorBoard and ensure that it covers a wider variety of use cases.

We have updated the existing dashboards (tabs) in TensorBoard to use the new API, so they serve as examples for plugin creators. For the current listing of plugins included within TensorBoard, you can explore the tensorboard/plugins directory on GitHub. For instance, observe the new plugin that generates precision-recall curves:
The plugin demonstrates the 3 parts of a standard TensorBoard plugin:
  • A TensorFlow summary op used to collect data for later visualization. [GitHub]
  • A Python backend that serves custom data. [GitHub]
  • A dashboard within TensorBoard built with TypeScript and polymer. [GitHub]
Additionally, like other plugins, the “pr_curves” plugin provides a demo that (1) users can look over in order to learn how to use the plugin and (2) the plugin author can use to generate example data during development. To further clarify how plugins work, we’ve also created a barebones TensorBoard “Greeter” plugin. This simple plugin collects greetings (simple strings preceded by “Hello, ”) during model runs and displays them. We recommend starting by exploring (or forking) the Greeter plugin as well as other existing plugins.

A notable example of how contributors are already using the TensorBoard API is Beholder, which was recently created by Chris Anderson while working on his master’s degree. Beholder shows a live video feed of data (e.g. gradients and convolution filters) as a model trains. You can watch the demo video here.
We look forward to seeing what innovations will come out of the community. If you plan to contribute a plugin to TensorBoard’s repository, you should get in touch with us first through the issue tracker with your idea so that we can help out and possibly guide you.

Acknowledgements
Dandelion Mané and William Chargin played crucial roles in building this API.



Harness the Power of Machine Learning in Your Browser with Deeplearn.js



Machine learning (ML) has become an increasingly powerful tool, one that can be applied to a wide variety of areas spanning object recognition, language translation, health and more. However, the development of ML systems is often restricted to those with computational resources and the technical expertise to work with commonly available ML libraries.

With PAIR — an initiative to study and redesign human interactions with ML — we want to open machine learning up to as many people as possible. In pursuit of that goal, we are excited to announce deeplearn.js 0.1.0, an open source WebGL-accelerated JavaScript library for machine learning that runs entirely in your browser, with no installations and no backend.
There are many reasons to bring machine learning into the browser. A client-side ML library can be a platform for interactive explanations, for rapid prototyping and visualization, and even for offline computation. And if nothing else, the browser is one of the world's most popular programming platforms.

While web machine learning libraries have existed for years (e.g., Andrej Karpathy's convnetjs) they have been limited by the speed of Javascript, or have been restricted to inference rather than training (e.g., TensorFire). By contrast, deeplearn.js offers a significant speedup by exploiting WebGL to perform computations on the GPU, along with the ability to do full backpropagation.

The API mimics the structure of TensorFlow and NumPy, with a delayed execution model for training (like TensorFlow), and an immediate execution model for inference (like NumPy). We have also implemented versions of some of the most commonly-used TensorFlow operations. With the release of deeplearn.js, we will be providing tools to export weights from TensorFlow checkpoints, which will allow authors to import them into web pages for deeplearn.js inference.

You can explore the potential of this library by training a convolutional neural network to recognize photos and handwritten digits — all in your browser without writing a single line of code.
We're releasing a series of demos that show deeplearn.js in action. Play with an image classifier that uses your webcam in real-time and watch the network’s internal representations of what it sees. Or generate abstract art videos at a smooth 60 frames per second. The deeplearn.js homepage contains these and other demos.

Our vision is that this library will significantly increase visibility and engagement with machine learning, giving developers access to powerful tools while simultaneously providing the everyday user with a way to interact with them. We’re looking forward to collaborating with the open source community to drive this vision forward.