Why does 'implay' or 'imshow' display a blank image for my matrix image data?

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MathWorks Support Team 2019-5-22

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https://ww2.mathworks.cn/matlabcentral/answers/466770-why-does-implay-or-imshow-display-a-blank-image-for-my-matrix-image-data

评论： Walter Roberson 2021-1-22

I have black and white image data that is stored in a matrix, 'img'. When I execute the following commands, I can see the image in black and white:

imagesc(img);
colormap(gray);

However, when I try to display the image using 'imshow' or view a sequence of similar images using 'implay', all I see is a white image. Why can't I see the image data?

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Answer 1

MathWorks Support Team 2019-6-13

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Try checking the range of your image data. 'imshow' and 'implay' will use a default display range for the data based on the data type. For example, if 'img' is an single or double type, then the display range is [0,1], where 0 maps to black and 1 maps to white. If 'img' is an integer type, the default display range will be the minimum and maximum representable values for that integer class. As an example, a uint16 array would have the range [0,65535].

If your data falls outside of the default range, you need to convert it. If you are using 'imshow', you can do so by specifying the 'DisplayRange' parameter. However, 'implay' does not have a parameter to adjust the display range so you will need to convert the matrix to a grayscale image. You can do so using 'mat2gray' and specifying the 'amin' and 'amax' parameters.