Recently I was going through the paper : "Intriguing Properties of Contrastive Losses"(https://arxiv.org/abs/2011.02803). In the paper(section 3.2) the authors try to determine how well the SimCLR framework has allowed the ResNet50 Model to learn good quality/generalised features that exhibit hierarchical properties. To achieve this, they make use of K-means on intermediate features of the ResNet50 model (intermediate means o/p of block 2,3,4..) & quote the reason -> "If the model learns good representations then regions of similar objects should be grouped together".
Final Results :
KMeans feature visualisation
I am trying to replicate the same procedure but with a different model (like VggNet, Xception), are there any resources explaining how to perform such visualisations ?
The procedure would be as follow:
Let us assume that you want to visualize the 8th layer from VGG. This layer's output might have the shape (64, 64, 256) (I just took some random numbers, this does not correspond to actual VGG). This means that you have 4096 256-dimensional vectors (for one specific image). Now you can apply K-Means on these vectors (for example with 5 clusters) and then color your image corresponding to the clustering result. The coloring is easy, since the 64x64 feature map represents a scaled down version of your image, and thus you just color the corresponding image region for each of these vectors.
I don't know if it might be a good idea to do the K-Means clustering on the combined output of many images, theoretically doing it on many images and one a single one should both give good results (even though for many images you probably would increase the number of clusters to account for the higher variation in your feature vectors).
Related
I am new to deep learning and Semantic segmentation.
I have a dataset of medical images (CT) in Dicom format, in which I need to segment tumours and organs involved from the images. I have labelled organs contoured by our physician which we call it RT structure stored in Dicom format also.
As far as I know, people usually use "mask". Does it mean I need to convert all the contoured structure in the rt structure to mask? or I can use the information from the RT structure (.dcm) directly as my input?
Thanks for your help.
There is a special library called pydicom that you need to install before you can actually decode and later visualise the X-ray image.
Now, since you want to apply semantic segmentation and you want to segment the tumours, the solution to this is to create a neural network which accepts as input a pair of [image,mask], where, say, all the locations in the mask are 0 except for the zones where the tumour is, which are marked with 1; practically your ground truth is the mask.
Of course for this you will have to implement your CustomDataGenerator() which must yield at every step a batch of [image,mask] pairs as stated above.
I'm a beginner in CNN DeepLearning, I know the basic concept that we use some filters to generate a set of feature maps from an image, we activate it using non-linear method like 'relu' before we downsample it. We keep doing this until the image becomes very small. Then we flatten it and use a fully connected network to calculate its category. And we use the back-propergation technique to calculate all parameters in the map. One thing I don't understand is that when we do Conv2D we create many filters(channels) from an image. Like in the sample code:
model.add(layers.Conv2D(32, (3, 3), activation='relu', input_shape=(150, 150, 3)))
I understand this is to generate as many features as possible. But how these filters are trained to detect different features from one image? If all of them are initialized with the same value (like 0) then they should end up with detecting the same feature, right? Are we giving them random values during initialization so that they can find their local minimum loss using gradient descent?
If you initialize all filters with the same value, then you are right, they will learn the same thing. That's why we never initialize with same value. We initialize each kernel with random values (usually 0 mean and some small variance).
There are many methods to find out a good initialization for your network. One of the most famous and used ones is Xavier initialization.
Adding to what being discussed, the weights in the CONV layer also learns the same way weights learn in FC layer, through backpropagation, using some optimization algorithm (GD, Adam, RMSprop etc). Ending up in local optimum is very unlikely in big networks as a point being local optimum for all the weights is very unlikely as no of weights increases. If weights are initialized with zeros, the gradients become the same for the update and hidden units become the same in a layer. Hence they learn the same features. Hence we use random initialization with mean 0 and variance inversely proportional to the number of units in the previous layer. (eg Xavier)
Is deep learning model supports multi-label classification problem or any other algorithms in H2O?
Orginal Response Variable -Tags:
apps, email, mail
finance,freelancers,contractors,zen99
genomes
gogovan
brazil,china,cloudflare
hauling,service,moving
ferguson,crowdfunding,beacon
cms,naytev
y,combinator
in,store,
conversion,logic,ad,attribution
After mapping them on the keys of the dictionary:
Then
Response variable look like this:
[74]
[156, 89]
[153, 13, 133, 40]
[150]
[474, 277, 113]
[181, 117]
[15, 87, 8, 11]
Thanks
No, H2O only contains algorithms that learn to predict a single response variable at a time. You could turn each unique combination into a single class and train a multi-class model that way, or predict each class with a separate model.
Any algorithm that creates a model that gives you "finance,freelancers,contractors,zen99" for one set of inputs, and "cms,naytev" for another set of inputs is horribly over-fitted. You need to take a step back and think about what your actual question is.
But in lieu of that, here is one idea: train some word embeddings (or use some pre-trained ones) on your answer words. You could then average the vectors for each set of values, and hope this gives you a good numeric representation of the "topic". You then need to turn your, say, 100 dimensional averaged word vector into a single number (PCA comes to mind). And now you have a single number that you can give to a machine learning algorithm, and that it can predict.
You still have a problem: having predicted a number, how do you turn that number into a 100-dim vector, and from there in to a topic, and from there into topic words? Tricky, but maybe not impossible.
(As an aside, if you turn the above "single number" into a factor, and have the machine learning model do a categorization, to predicting the most similar topic to those it has seen before... you've basically gone full circle and will get a model identical to the one you started with that has too many classes.)
I am currently looking into multi-labeling classification and I have some questions (and I couldn't find clear answers).
For the sake of clarity let's take an example : I want to classify images of vehicles (car, bus, truck, ...) and their make (Audi, Volkswagen, Ferrari, ...).
So I thought about training two independant CNN (one for the "type" classification and one fore the "make" classifiaction) but I thought it might be possible to train only one CNN on all the classes.
I read that people tend to use sigmoid function instead of softmax to do that. I understand that sigmoid does not sum up to 1 like softmax does but I dont understand in what doing that enables to do multi-labeling classification ?
My second question is : Is it possible to take into account that some classes are completly independant ?
Thridly, in term of performances (accuracy and time to give the classification for a new image), isn't training two independant better ?
Thank you for those who could give my some answers or some ideas :)
Softmax is a special output function; it forces the output vector to have a single large value. Now, training neural networks works by calculating an output vector, comparing that to a target vector, and back-propagating the error. There's no reason to restrict your target vector to a single large value, and for multi-labeling you'd use a 1.0 target for every label that applies. But in that case, using a softmax for the output layer will cause unintended differences between output and target, differences that are then back-propagated.
For the second part: you define the target vectors; you can encode any sort of dependency you like there.
Finally, no - a combined network performs better than the two halves would do independently. You'd only run two networks in parallel when there's a difference in network layout, e.g. a regular NN and CNN in parallel might be viable.
In the below code, they use autoencoder as supervised clustering or classification because they have data labels.
http://amunategui.github.io/anomaly-detection-h2o/
But, can I use autoencoder to cluster data if I did not have its labels.?
Regards
The deep-learning autoencoder is always unsupervised learning. The "supervised" part of the article you link to is to evaluate how well it did.
The following example (taken from ch.7 of my book, Practical Machine Learning with H2O, where I try all the H2O unsupervised algorithms on the same data set - please excuse the plug) takes 563 features, and tries to encode them into just two hidden nodes.
m <- h2o.deeplearning(
2:564, training_frame = tfidf,
hidden = c(2), auto-encoder = T, activation = "Tanh"
)
f <- h2o.deepfeatures(m, tfidf, layer = 1)
The second command there extracts the hidden node weights. f is a data frame, with two numeric columns, and one row for every row in the tfidf source data. I chose just two hidden nodes so that I could plot the clusters:
Results will change on each run. You can (maybe) get better results with stacked auto-encoders, or using more hidden nodes (but then you cannot plot them). Here I felt the results were limited by the data.
BTW, I made the above plot with this code:
d <- as.matrix(f[1:30,]) #Just first 30, to avoid over-cluttering
labels <- as.vector(tfidf[1:30, 1])
plot(d, pch = 17) #Triangle
text(d, labels, pos = 3) #pos=3 means above
(P.S. The original data came from Brandon Rose's excellent article on using NLTK. )
In some aspects encoding data and clustering data share some overlapping theory. As a result, you can use Autoencoders to cluster(encode) data.
A simple example to visualize is if you have a set of training data that you suspect has two primary classes. Such as voter history data for republicans and democrats. If you take an Autoencoder and encode it to two dimensions then plot it on a scatter plot, this clustering becomes more clear. Below is a sample result from one of my models. You can see a noticeable split between the two classes as well as a bit of expected overlap.
The code can be found here
This method does not require only two binary classes, you could also train on as many different classes as you wish. Two polarized classes is just easier to visualize.
This method is not limited to two output dimensions, that was just for plotting convenience. In fact, you may find it difficult to meaningfully map certain, large dimension spaces to such a small space.
In cases where the encoded (clustered) layer is larger in dimension it is not as clear to "visualize" feature clusters. This is where it gets a bit more difficult, as you'll have to use some form of supervised learning to map the encoded(clustered) features to your training labels.
A couple ways to determine what class features belong to is to pump the data into knn-clustering algorithm. Or, what I prefer to do is to take the encoded vectors and pass them to a standard back-error propagation neural network. Note that depending on your data you may find that just pumping the data straight into your back-propagation neural network is sufficient.