display rescaled matrix as image: imagesc vs wcodemat

Question

Yuji Zhang 2015-4-4

0
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https://ww2.mathworks.cn/matlabcentral/answers/196029-display-rescaled-matrix-as-image-imagesc-vs-wcodemat

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Hi I tried two ways to rescale a matrix and display as an image: imagesc and wcodemat.

Worded well in Fig 1. But in figure 2: wcodemat changes the distribution of the numbers.

Can somebody tell me what's the cause? Thanks a lot!

The cat data can be downloaded here http://spark-public.s3.amazonaws.com/compmethods/Lecture%20Note%20Packet/catData.mat

My code is here:

%%test with woman
load woman;
% Get the range of the colormap
NBCOL = size(map,1);
% Obtain the 2D dwt using the Haar wavelet
[cA1,cH1,cV1,cD1] = dwt2(X,'db1');
figure;
% Display without scaling
subplot(2,3,1);
image(cA1);
colormap(map);
axis image; colorbar;
title('Unscaled Image');
subplot(2,3,4); hist(cA1);
% rescale with wcodemat
subplot(2,3,2);
image(wcodemat(cA1,NBCOL));
colormap(map);
axis image; colorbar;
title('Rescale w/ wcodemat');
subplot(2,3,5); hist(wcodemat(cA1,NBCOL));
% rescale with imagesc
subplot(2,3,3); 
imagesc(cA1); axis image; colorbar;
title('Rescale w/ imagesc');
%%test with cat
load catData % each column is a 64*64 pixel (greyscale) picture, reshaped
% source: http://spark-public.s3.amazonaws.com/compmethods/Lecture%20Note%20Packet/catData.mat
p = double( reshape(cat(:,2),64,64) );
[cA, cH, cV, cD] = dwt2(p,'haar');
% Discrete wavelet transform, 2D.
% ch, cv, and cd are not scale 0-255
% cA is 1st level wavelet, and cH, cV, cD are 2nd level
contour1 = cH + cV;
figure(2);
subplot(2,3,1); image(contour1); axis image; colorbar;
title('Contour, un-rescaled');
subplot(2,3,4); hist(contour1);
subplot(2,3,2); imagesc(contour1); axis image; colorbar;
title('Contour, rescaled w/ imagesc');
% iamgesc scales the matrix and display the image
% now rescale the matrix manually
NBCOL = size(colormap(gray),1);
subplot(2,3,3);
contour2 = wcodemat(contour1, NBCOL);
image(contour2); axis image; colorbar;
title('Contour, rescaled w/ wcodemat');
subplot(2,3,6); hist(contour2);