How can I use indexed image in neural network ?

I have converted RGB images into indexed images using function rgb2ind then I made their matrix and load it using the code

fprintf('Loading and Visualizing Data ...\n')

load('ClothingData.mat');
m = size(X, 1);
[sel] = randperm(size(X, 1)); % Randomly select 100 data points to display
sel = sel(1:100);

displayData(X(sel, :));

but it is throwing this error message

Warning: Size vector should be a
row vector with integer elements. 
> In displayData at 30
  In ex4 at 50 
Error using reshape
Size arguments must be real
integers.

Please tell me how to fix this error, also can I use indexed images for neural network classification or not

[Walter Roberson]

displayData does not appear to be a Mathworks routine, and also does not appear to be part of the File Exchange.

[Walter Roberson]

Is displayData from https://github.com/aptiva0985/MachineLearning-Andrew-Ng-Coursera-/blob/master/ML003/mlclass-ex3/displayData.m ?

Answer 1

[Walter Roberson]

"can I use indexed images for neural network classification or no"

Yes.

If you are doing pattern matching, you might even get a useful result. But don't expect anything useful even for pattern matching unless you passed a fixed colormap into rgb2ind(). And even in that case, if you did not do illumination correction, your results might be low quality.

[Walter Roberson]

For https://github.com/aptiva0985/MachineLearning-Andrew-Ng-Coursera-/blob/master/ML003/mlclass-ex3/displayData.m if you do not pass a second parameter, then the number of elements you pass in must be the square of an integer.

[jawad ashraf]

my image dimension is 64 x 94. Do you mean I should use square image like 100 x 100 or 60 x 60 ?

[Walter Roberson]

Yes. However you might find it easier to just pass in the width of your image as the second parameter. The problem only occurs if you omit the second parameter.

[jawad ashraf]

By using squared images it is displaying data but not all of data is showing. Most of elements are missing moreover it is grayscale but my images are quantized.

[Walter Roberson]

Call colormap() passing in the appropriate colormap array after you call displayData()

[jawad ashraf]

% Load Training Data
fprintf('Loading and Visualizing Data ...\n')

% load('myclothingdata.mat');
load('myclothingdata.mat');
m = size(X, 1);

% Randomly select 100 data points to display
[sel] = randperm(size(X, 1));
sel = sel(1:100);

displayData(X(sel, :));
colormap()
fprintf('Program paused. Press enter to continue.\n');

Dear I have called colormap() after calling displaydata() but it is not working, still showing grayscale images. Please tell where is the proper place to write this function and how? thanks

[Walter Roberson]

You do not pass in the name of a color map. You indicated that these are indexed images, so somewhere you must have an array that relates X values to color: you need to colormap() that array.

[jawad ashraf]

Sorry I don't know how to make a colormap() array and relate it to my indexed images which are contained in X. Can you guide me as I am new in Matlab. thanks

[Walter Roberson]

What does "indexed image" mean to you? If one of the pixels has value (say) 4, then what color should the pixel be?

[Walter Roberson]

Please show the output of

whos -file myclothingdata.mat

[jawad ashraf]

According to my understanding we should have two matrices

• First should contain our indexed images called X
• Other should be a colormap matrix map containing floating-point values in the range [0, 1].

For now I have just X matrix(vector) which contains my indexed images.

(detail) Actually I converted my original RGB images of clothes into indexed images using rgb2ind function of matlab and saved all these indexed images in a separate folder. In next step I made the vector X of all these indexed images. Now whenever I try to display my indexed images data using DisplayData (a custom function) it shows yellow images of clothes as shown in figure above. I just want to know how can I show colored images using colormap(). How to make colormap matrix(or array) in my code and map it to data matrix X. I don't know the procedure. I'll be grateful if you guide me in a proper way. Thanks [e-mail]

[jawad ashraf]

I am following the code of Andrew NGs assignment 3 and 4

[Walter Roberson]

In order for the rgb2ind to be done consistently, you need to generate a colormap that you use for all of the images. For example you could pick one of the images and use

[first_ind_image, map] = rgb2ind(first_rgb_image);

and after that you would use

rgb2ind(other_image, map)

And then when you went to display, you would

colormap(map)