Improve classification speed

[maelh]

I haven’t tested it out yet, but this link provides some interesting hints, especially also on adapting models with layers before. Also the image size used is much smaller:

Black and white images on VGG16

For the first week assigment I am trying to do the Facial Expression Recognition Challenge (https://www.kaggle.com/c/challenges-in-representation-learning-facial-expression-recognition-challenge) However, I have some problems using VGG16 to grayscale images. I am using keras 2.0.2 with Tensorflow 1.0.1. I am using directly the keras.application module. Here is my code. from keras.applications.vgg16 import VGG16 from keras_tqdm import TQDMNotebookCallback from keras.preprocessing import imag…

Checking this link however, that says it’s slow to train, makes me assume it might be slow in inference as well:

VGG16 - Convolutional Network for Classification and Detection

The following is on intuition for choosing the right image size wrt. to recognition rate:

Lecture7-Changing Image Input Size

At the first 10 mins of the lecture, Jeremy finetuned a resnet model, and changed its input size to 400 by 400. I’m wondering why did that made a good improvement in the classification accuracy, and how can some one with intuition decides whether or not this would make an improvement or not. Also i navigated through resnet and found that changing input size, doesn’t change any parameters except for the last dense layer which will be replaced when finetuning. So I’m wondering if someone needs…

So in my case small images with low noise (maybe using some Gaussian filter) should work well, since I have pretty distinct lanes delimited by white paper.

Compression from the video streaming could be an issue, and that compression noise should be eliminated as much as possible. Flickering or changing brightness may be an issue as well. So I will have to find a way to test how well the images were stabilized and if a Gaussian filter is sufficient to filter out “grainy” images and compression artifacts.
Probably filtering is best applied before training, and before feeding it into the trained model (i.e. inferencing).

Also, it seems the input size for VGG16 is made for 224 x 224 RGB images, so no improvement there compared to resnet18.

A good discussion about many relevant details is here:

Lesson 6 In-Class Discussion

This great review is a great read. It came out two days ago from Google, by Margaret Mitchell and Ben Hutchinson, titled 50 Years of Test (Un)fairness: Lessons for Machine Learning

My understanding:
So CNNs will deal with any image size, as long as the kernel(s) can be applied (i.e., they should be at least as large as the kernel’s resolution and channel depth) and you have “summarizing” layers later, that can deal with any number of inputs.

Still have to see if fastai does any implicit resizing of input images.

The accuracy might suffer if image details/features are lacking that the pretrained model tries to extract. The question is if this could also cause misidentification of features that do not exist in the input image at all, or if it will simply not detect those features for which the details are lacking (which would be fine, since I only want to detect details that are clearly visible even at low resolution, i.e., the lane boundaries).

So image input size would affect the performance of a forward pass, even with an unchanged CNN model, because the kernel will slide across the entire image, and how many slide “steps” it takes depends on the image size.