To prepare large amounts of data sets for training deep learning-based image classification models, we usually have to rely on image augmentation methods. I would like to know what are the usual image augmentation algorithms, are there any considerations when choosing them?
The litterature on data augmentation is very very large and very dependent on your kind of applications.
The first things that come to my mind are the galaxy competition's rotations and Jasper Snoeke's data augmentation.
But really all papers have their own tricks to get good scores on special datasets for exemples stretching the image to a specific size before cropping it or whatever and this in a very specific order.
More practically to train models on the likes of CIFAR or IMAGENET use random crops and random contrast, luminosity perturbations additionally to the obvious flips and noise addition.
Look at the CIFAR-10 tutorial on TF website it is a good start. Plus TF now has random_crop_and_resize() which is quite useful.
EDIT: The papers I am referencing here and there.
It depends on the problem you have to address, but most of the time you can do:
Rotate the images
Flip the image (X or Y symmetry)
Add noise
All the previous at the same time.
Related
Im currently working on a classification project but I'm in doubt about how I should start off.
Goal
Accurately classifying pictures of size 80*80 (so 6400 pixels) in the correct class (binary).
Setting
5260 training samples, 600 test samples
Question
As there are more pixels than samples, it seems logic to me to 'drop' most of the pixels and only look at the important ones before I even start working out a classification method (like SVM, KNN etc.).
Say the training data consists of X_train (predictors) and Y_train (outcomes). So far, I've tried looking at the SelectKBest() method from sklearn for feature extraction. But what would be the best way to use this method and to know how many k's I've actually got to select?
It could also be the case that I'm completely on the wrong track here, so correct me if I'm wrong or suggest an other approach to this if possible.
You are suggesting to reduce the dimension of your feature space. That is a method of regularization to reduce overfitting. You haven't mentioned overfitting is an issue so I would test that first. Here are some things I would try:
Use transfer learning. Take a pretrained network for image recognition tasks and fine tune it to your dataset. Search for transfer learning and you'll find many resources.
Train a convolutional neural network on your dataset. CNNs are the go-to method for machine learning on images. Check for overfitting.
If you want to reduce the dimensionality of your dataset, resize the image. Going from 80x80 => 40x40 will reduce the number of pixels by 4x, assuming your task doesn't depend on fine details of the image you should maintain classification performance.
There are other things you may want to consider but I would need to know more about your problem and its requirements.
I am working on a limited number of large size images, each of which can have 3072*3072 pixels. To train a semantic segmentation model using FCN or U-net, I construct a large sample of training sets, each training image is 128*128.
In the prediction stage, what I do is to cut a large image into small pieces, the same as trainning set of 128*128, and feed these small pieces into the trained model, get the predicted mask. Afterwards, I just stitch these small patches together to get the mask for the whole image. Is this the right mechanism to perform the semantic segmentation against the large images?
Your solution is often used for this kind of problem. However, I would argue that it depends on the data if it truly makes sense. Let me give you two examples you can still find on kaggle.
If you wanted to mask certain parts of satellite images, you would probably get away with this approach without a drop in accuracy. These images are highly repetitive and there's likely no correlation between the segmented area and where in the original image it was taken from.
If you wanted to segment a car from its background, it wouldn't be desirable to break it into patches. Over several layers the network will learn the global distribution of a car in the frame. It's very likely that the mask is positive in the middle and negative in the corners of the image.
Since you didn't give any specifics what you're trying to solve, I can only give a general recommendation: Try to keep the input images as large as your hardware allows. In many situation I would rather downsample the original images than breaking it down into patches.
Concerning the recommendation of curio1729, I can only advise against training on small patches and testing on the original images. While it's technically possible thanks to fully convolutional networks, you're changing the data to an extend, that might very likely hurt performance. CNNs are known for their extraction of local features, but there's a large amount of global information that is learned over the abstraction of multiple layers.
Input image data:
I would not advice feeding the big image (3072x3072) directly into the caffe.
Batch of small images will fit better into the memory and parallel programming will too come into play.
Data Augmentation will also be feasible.
Output for big Image:
As for the output of big Image, you better recast the input size of FCN to 3072x3072 during test phase. Because, layers of FCN can accept inputs of any size.
Then you will get 3072x3072 segmented image as output.
I am currently trying to make a program to differentiate rotten oranges and edible oranges solely based on their external appearance. To do this, I am planning on using a Convolutional Neural Network to train with rotten oranges and normal oranges. After some searching I could only find one database of approx. 150 rotten oranges and 150 normal oranges on a black background (http://www.cofilab.com/downloads/). Obviously, a machine learning model will need at least few thousand oranges to achieve an accuracy above 90 or so percent. However, can I alter these 150 oranges in some way to produce more photos of oranges? By alter, I mean adding different shades of orange on the citrus fruit to make a "different orange." Would this be an effective method of training a neural network?
It is a very good way to increase the number of date you have. What you'll do depends on your data. For example, if you are training on data obtained from a sensor, you may want to add some noise to the training data so that you can increase your dataset. After all, you can expect some noise coming from the sensor later on.
Assuming that you will train it on images, here is a very good github repository that provides means to use those techniques. This python library helps you with augmenting images for your machine learning projects. It converts a set of input images into a new, much larger set of slightly altered images.
Link: https://github.com/aleju/imgaug
Features:
Most standard augmentation techniques available.
Techniques can be applied to both images and keypoints/landmarks on
images. Define your augmentation sequence once at the start of the
experiment, then apply it many times.
Define flexible stochastic ranges for each augmentation, e.g. "rotate
each image by a value between -45 and 45 degrees" or "rotate each
image by a value sampled from the normal distribution N(0, 5.0)".
Easily convert all stochastic ranges to deterministic values to
augment different batches of images in the exactly identical way
(e.g. images and their heatmaps).
Data augmentation is what you are looking for. In you case you can do different things:
Apply filters to get slightly different image, as has been said you can use gaussian blur.
Cut the orange and put it in different backgrounds.
Scale the oranges with different scales factors.
Rotate the images.
create synthetic rotten oranges.
Mix all different combinations of the previous mentioned. With this kind of augmentation you can easily create thousand of different oranges.
I did something like that with a dataset of 12.000 images and I can create 630.000 samples
That is indeed a good way to increase your data set. You can, for example, apply Gaussian blur to the images. They will become blurred, but different from the original. You can invert the images too. Or, in last case, look for new images and apply the cited techniques.
Data augmentation is really good way to boost training set but still not enough to train a deep network end to end on its own given the possibility that it will overfit. You should look at domain adaptation where you take a pretrained model like inception which is trained on imagenet dataset and finetune it for your problem. Since you have to learn only parameters required to classify your use case, it is possible to achieve good accuracies with relatively less training data available. I have hosted a demo of classification with this technique here. Try it out with your dataset and see if it helps. The demo takes care of pretrained model as well as data augmentation for dataset that you will upload.
I am trying to classify a series of images like this one, with each class of comprising images taken from similar cellular structure:
I've built a simple network in Keras to do this, structured as:
1000 - 10
The network unaltered achieves very high (>90%) accuracy on MNIST classification, but almost never higher than 5% on these types of images. Is this because they are too complex? My next approach would be to try stacked deep autoencoders.
Seriously - I don't expect any nonconvolutional model to work well on this type of data.
A nonconv net for MNIST works well because the data is well preprocessed (it is centered in the middle and resized to certain size). Your images are not.
You may notice (on your pictures) that certain motifs reoccure - like this darker dots - with different positions and sizes - if you don't use convolutional model you will not capture that efficiently (e.g. you will have to recognize a dark dot moved a little bit in the image as a completely different object).
Because of this I think that you should try convolutional MNIST model instead classic one or simply try to design your own.
First question, is if you run the training longer do you get better accuracy? You may not have trained long enough.
Also, what is the accuracy on training data and what is the accuracy on testing data? If they are both high, you can run longer or use a more complex model. If training accuracy is better than testing accuracy, you are essentially at the limits of your data. (i.e. brute force scaling of model size wont help, but clever improvements might, i.e. try convolutional nets)
Finally, complex and noisy data you may need a lot of data to make a reasonable classification. So you need many, many images.
Deep stacked autoencoders, as I understand it is an unsupervised method, which isn't directly suitable for classification.
I'v got a binary classification problem. I'm trying to train a neural network to recognize objects from images. Currently I've about 1500 50x50 images.
The question is whether extending my current training set by the same images flipped horizontally is a good idea or not? (images are not symetric)
Thanks
I think you can do this to a much larger extent, not just flipping the images horizontally, but changing the angle of the image by 1 degree. This will result in 360 samples for every instance that you have in your training set. Depending on how fast your algorithm is, this may be a pretty good way to ensure that the algorithm isn't only trained to recognize images and their mirrors.
It's possible that it's a good idea, but then again, I don't know what's the goal or the domain of the image recognition. Let's say the images contain characters and you're asking the image recognition software to determine if an image contains a forward slash / or a back slash \ then flipping the image will make your training data useless. If your domain doesn't suffer from such issues, then I'd think it's a good idea to flip them and even rotate with varying degrees.
I have used flipped images in AdaBoost with great success in the course: http://www.csc.kth.se/utbildning/kth/kurser/DD2427/bik12/Schedule.php
from the zip "TrainingImages.tar.gz".
I know there are some information on pros/cons with using flipped images somewhere in the slides (at the homepage) but I can't find it. Also a great resource is http://www.csc.kth.se/utbildning/kth/kurser/DD2427/bik12/DownloadMaterial/FaceLab/Manual.pdf (together with the slides) going thru things like finding things in different scales and orientation.
If the images patches are not symmetric I don't think its a good idea to flip. Better idea is to do some similarity transforms to the training set with some limits. Another way to increase the dataset is to add gaussian smoothed templates to it. Make sure that the number of positive and negative samples are proportional. Too many positive and too less negative might skew the classifier and give bad performance on testing set.
It depends on what your NN is based on. If you are extracting rotation invariant features or features that do not depend on the spatial position within the the image (like histograms or whatever) and train your NN with these features, then rotating will not be a good idea.
If you are training directly on pixel values, then it might be a good idea.
Some more details might be useful.