Deep into tensorboard for pytorch

Google’s tensorflow’s tensorboard is a web server to serve visualizations of the training progress of a neural network, it visualizes scalar values, images, text, etc.; these information are saved as events in tensorflow. It’s a pity that other deep learning frameworks lack of such tool, so there are already packages letting users to log the events without tensorflow; however they only provides basic functionalities. The purpose of this package is to let researchers use a simple interface to log events within PyTorch (and then show visualization in tensorboard). This package currently supports logging scalar, image, audio, histogram, text, embedding, and the route of back-propagation. The following manual is tested on Ubuntu and Mac, and the environment are anaconda’s python2 and python3.

Install tensorboard for PyTorch

Simply type pip install tensorboard-pytorch under bash to install this package. To use the newest version, you might need to build from source or pip install tensorboard-pytorch —-no-cache-dir.

Install tensorboard server

To run tensorboard web server, you need to install tensorflow by pip install tensorflow or pip install tensorflow-gpu. After that, type tensorboard --logdir=[yourlogdir] to start the server, where yourloaddir is the parameter of the object constructor. I think this command is tedious, so I add a line alias tb='tensorboard --logdir 'in ~/.bash_profile. In this way, the above command is simplified as tb [yourlogdir]. Use your favorite browser to load the tensorboard page, the address will be shown in the terminal after starting the server.

general usage:

Create an event writer instance

Before logging anything, we need to create a writer instance. This can be done with:

from tensorboard import SummaryWriter 
#SummaryWriter encapsulates everything
writer = SummaryWriter('runs/exp-1')
#creates writer object. The log will be saved in 'runs/exp-1'
writer2 = SummaryWriter()
#creates writer2 object with auto generated file name, the dir will be something like 'runs/Aug20-17-20-33'
writer3 = SummaryWriter(comment='3x learning rate')
#creates writer2 object with auto generated file name, the comment will be appended to the filename. The dir will be something like 'runs/Aug20-17-20-33-3xlearning rate'

Each subfolder will be treated as different experiments in tensorboard. Each time you re-run the experiment with different settings, you should change the name of the sub folder such as runs/exp2, runs/myexp so that you can easily compare different experiment settings. Type tb runs to compare different runs in tensorboard.

Save scalar value

Scalar value is the most simple data type to deal with. Mostly we save the loss value of each training step, or the accuracy after each epoch. Sometimes I save the corresponding learning rate as well. It’s cheap to save scalar value. Just log anything you think is important. To log a scalar value, use writer.add_scalar('myscalar', value, iteration). Note that the program complains if you feed a PyTorch variable. Remember to extract the scalar value by[0] if x is a torch variable.

Save image

An image is represented as 3-dimensional tensor. The simplest case is save one image at a time. In this case, the image should be passed as a 3-dimension tensor of size [3, H, W]. The three dimensions correspond to R, G, B channel of an image. After your image is computed, use writer.add_image('imresult', x, iteration) to save the image. If you have a batch of images to show, use torchvision's make_grid function to prepare the image array and send the result to add_image(...). ps. make_grid takes a 4D tensor and returns tiled images in 3D tensor.

Save histogram

Saving histogram is expensive. Both in computation time and storage. If training slows down after using this package, check this first. To save a histogram, convert the array into numpy array and save with writer.add_histogram('hist', array, iteration) .

Save audio with writer.add_audio('myaudio', audio, iteration)

Currently the sampling rate of the this function is fixed at 44100 KHz, single channel. The input of the add_audio function is a one dimensional array, with each element representing the consecutive amplitude samples. For a 2 seconds audio, the input x should have 88200 elements. Each element should lie in [-1, 1].

Save text with writer.add_text('mytext','this is a pen', iteration)

This one is trivial:)

Save graph of the network model (EXPERIMENTAL)

Graph drawing is based on autograd’s backward tracing. It goes along the next_functions attribute in a variable recursively, drawing each encountered nodes. To draw the graph, you need a model m and an input variable t that have correct size for m. Let r = m(t), then please invoke writer.add_graph(m, r)to save the graph. By default, the input tensor does not require gradient, therefore it will be omitted when back tracing. To draw the input node, pass an additional parameter requires_grad=True when creating the input tensor. See for complete example.

Save embedding visualization

Embedding is a technique to visualize high dimensional data. To convert high dimensional data into human perceptible 3D data, tensorboard provides PCA and t-sne to project the data into low dimensional space. What you need to do is provide a bunch of points and tensorboard will do the rest for you. The bunch of points is passed as a tensor of size n x d ,where n is the number of points and d is the feature dimension. The feature representation can either be raw data (e.g. the mnist image) or a representation learned by your network (extracted feature). This determines how the points distributes. To make the visualization more informative, you can pass optional metadata or label_imgs for each data points. In this way you can see that neighboring point have similar label and distant points have very different label (semantically or visually). Here the metadata is a list of labels, and the length of the list should equal to n, the number of the points. The label_imgs is a 4D tensor of size NCHW. N should equal to n as well. See for complete example.

other tips (of tensorboard):

Logging is cheap, but display is expensive.

For my experience, if there are 3 or more experiments to show at a time and each experiment have, say, 50K points, tensorboard might need a lot of time to present the data.

Grouping plots

Usually, there are many numbers to log in one experiment. For example, when training GANs you should log the loss of the generator, discriminator. If the loss is composed of two other loss functions, say L1 and MSE, you might want to log the value of the other two losses as well. In this case, you can write the tags as Gen/L1, Gen/MSE, Desc/L1, Desc/MSE. In this way, tensorboard will group the plots into two sections (Gen, Desc). You can also use the regular expression to filter data.

Modify the tick of sliding bar

The default number of tick points for the sliding bar is 10. To make it more dense, just modify the hardcoded event_accumulator in~/anaconda3/lib/python3.6/site-packages/tensorflow/tensorboard/backend/ as you wish.