A form of signal processing where the input is an image. Usually treating the digital image as a two-dimensional signal (or multidimensional). This processing may include image restoration and enhancement (in particular, pattern recognition and projection).
Questions tagged [image-processing]
566 questions
137
votes
5 answers
Why normalize images by subtracting dataset's image mean, instead of the current image mean in deep learning?
There are some variations on how to normalize the images but most seem to use these two methods:
Subtract the mean per channel calculated over all images (e.g. VGG_ILSVRC_16_layers)
Subtract by pixel/channel calculated over all images (e.g. CNN_S,…
Max Gordon
- 5,616
- 8
- 30
- 51
109
votes
7 answers
Detecting a given face in a database of facial images
I'm working on a little project involving the faces of twitter users via their profile pictures.
A problem I've encountered is that after I filter out all but the images that are clear portrait photos, a small but significant percentage of twitter…
ʞɔıu
- 1,107
- 2
- 8
- 5
78
votes
1 answer
How does a simple logistic regression model achieve a 92% classification accuracy on MNIST?
Even though all the images in the MNIST dataset are centered, with a similar scale, and face up with no rotations, they have a significant handwriting variation that puzzles me how a linear model achieves such a high classification accuracy.
As far…
Nitish Agarwal
- 813
- 4
- 6
77
votes
2 answers
ImageNet: what is top-1 and top-5 error rate?
In ImageNet classification papers top-1 and top-5 error rates are important units for measuring the success of some solutions, but what are those error rates?
In ImageNet Classification with Deep Convolutional
Neural Networks
by Krizhevsky et al.…
daniel451
- 2,635
- 6
- 22
- 26
74
votes
2 answers
What is the difference between ZCA whitening and PCA whitening?
I am confused about ZCA whitening and normal whitening (which is obtained by dividing principal components by the square roots of PCA eigenvalues). As far as I know,
$$\mathbf x_\mathrm{ZCAwhite} = \mathbf U \mathbf x_\mathrm{PCAwhite},$$ where…
RockTheStar
- 11,277
- 31
- 63
- 89
48
votes
5 answers
How to assess the similarity of two histograms?
Given two histograms, how do we assess whether they are similar or not?
Is it sufficient to simply look at the two histograms?
The simple one to one mapping has the problem that if a histogram is slightly different and slightly shifted then we'll…
Mew 3.4
- 591
- 1
- 5
- 5
42
votes
4 answers
Entropy of an image
What is the most information/physics-theoretical correct way to compute the entropy of an image? I don't care about computational efficiency right now - I want it theoretically as correct as possible.
Lets start with a gray-scale image. One…
Davor Josipovic
- 948
- 1
- 12
- 19
38
votes
1 answer
Why do we need to normalize the images before we put them into CNN?
I am not clear the reason that we normalise the image for CNN by (image - mean_image)? Thanks!
Zhi Lu
- 717
- 3
- 8
- 11
35
votes
3 answers
What is the most accurate way of determining an object's color?
I have written a computer program that can detect coins in a static image (.jpeg, .png, etc.) using some standard techniques for computer vision (Gaussian Blur, thresholding, Hough-Transform etc.). Using the ratios of the coins picked up from a…
MoonKnight
- 707
- 9
- 22
29
votes
4 answers
Does the image format (png, jpg, gif) affect how an image recognition neural net is trained?
I'm aware that there's been lots of advances with regards to image recognition, image classification, etc with deep, convolutional neural nets.
But if I train a net on, say, PNG images, will it only work for images so encoded? What other image…
Felipe
- 990
- 2
- 10
- 18
24
votes
6 answers
How does neural network recognise images?
I am trying to learn how Neural Network works on image recognition. I have seen some examples and become even more confused. In the example of letter recognition of a 20x20 image, the values of each pixel become the input layer. So 400 neurons. Then…
user1731927
- 359
- 1
- 3
- 5
23
votes
3 answers
How to calculate number of features based on image resolution?
Just covered Andrew Ng's Non-linear Hypothesis of Neural Netowrks, and we had a multiple choice question for determining number of features for an image of resolution 100x100 of grescale intensities.
And the answer was 50 million, $5$ x…
Iancovici
- 735
- 2
- 5
- 17
21
votes
2 answers
What are the differences between the Baum-Welch algorithm and Viterbi training?
I am currently using Viterbi training for an image segmentation problem. I wanted to know what the advantages/disadvantages are of using the Baum-Welch algorithm instead of Viterbi training.
Mykie
- 491
- 1
- 3
- 9
21
votes
4 answers
Comparing two histograms using Chi-Square distance
I want to compare two images of faces. I calculated their LBP-histograms. So now I need to compare these two histograms and get something that will tell how much these histograms are equal (0 - 100%).
There are many ways of solving this task, but…
Anton Holovin
- 313
- 1
- 2
- 6
18
votes
2 answers
What does a bottleneck layer mean in neural networks?
I was reading the FaceNet paper and in the 3rd paragraph of the introduction it says:
Previous face recognition approaches based on deep networks
use a classification layer trained over a set of
known face identities and then take an…
YellowPillow
- 1,031
- 2
- 9
- 16