MATLAB: How to convert 0-255 scale to 30-170 scale in a grayscale Image

contrast stretchimage processingImage Processing Toolboxrescale

I have a 112*112 matrix in matlab which I am plotting as a grayscale image. I am using imacesc for this purpose and the resulting image is on a normal grayscale image, 0-255. However, the results are not quite pronounced in this scale and I want to rescale my image on a scale of 30 – 170 since most of my pixel values are in this range. I am using rescale for this purpose but it is not working. Can anyone help me with this issue?

Best Answer

Try telling imshow() the display range:

imshow(grayImage, [30, 170]);

but rescale() should have worked also:

imshow(rescale(grayImage, 30, 170), []); % Use [] because I think rescale() returns a double.

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MATLAB: How to change colortype truecolor to grayscale

You have to display the gray scale image with imshow() after you do the conversion.

grayImage = rgb2gray(rgbImage);
imshow(grayImage, []);  % You probably forgot to do this step.

MATLAB: Scale ksdensity

The output of ksdensity() is scaled so that the area under the curve is equal to 1, which is conventional for a probability density function. Using your notation, this means that

sum(xi.*diff([0,f]))

will be approximately 1.

If you want your red lines to be about the same height as the curve, you will need to multiply one or the other before plotting. For example, use the following line to use shorter red lines. (I also commented out your manual rescaling.)

plot(f,xi);line(repmat(X,2,1),repmat([0;0.01],1,length(X)),'color','r' );%axis([a b 0 40]);

If you really want to use two different scales, then you can use the plotyy() command.

Best Answer

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MATLAB: How to change colortype truecolor to grayscale

MATLAB: Scale ksdensity

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