How can I use wcodemat to re-scale an intensity/gray-scale image?

I want to change my original intensity/gray-scale image into wcodemat for wavelet transform but problem is if i use

Y = wcodemat(X)

the image just turn into different shades of blue and this doesn't represent the original image(which is black and grey), I also cannot use

Y = wcodemat(X,NBCODES), because my image doesn't have map which is required for the NBCODES parameter.

How can I resolve this problem?

Answer 1

[Chaya N]

You could get a map of your original grayscale image X using the contrast function

 cmap = contrast(X)

This would give you a map of size CurrentGrayMap-by-3 which you could use when plotting your scaled image

[Akshra]

Hi, thank you very much for your answer, the cmap does work in order to use the format

Y = wcodemat(X,NBCODES)

However, when i tried to rescale the image using cmap and wcodemat, the image doesn't look exactly like the original image. Why can't I get a true/actual image when I rescale it?

Also when I use wcodemat for an indexed image, there is no difference between the original image and re-scaled image but why doesn't this apply to my intensity image. I have attached the output of the rescaled input image.

Do you have any idea why this happens and how to resolve this?

[Akshra]

[Akshra]

figure on the left is the original image and figure on the right is the re-scaled image using cmap.

[Chaya N]

Can you post the relevant code here? When calling wcodemat, you may need to call with the same NBCODES value as the length of the current colormap. If this length is small compared to the number of distinct gray levels you require for a smoother looking scaled image, then it appears 'thresholded' or having excess contrast as in your figure on the right. I would suggest you manually try to obtain as large a map length as possible. For an 8-bit image, this is usually 255-by-3. For example, you could obtain a 255 length colormap from your original image and call wcodemat with the same NBCODES=255.