Why the image color bar doesn't contain certain color (Red, in particular)

Question

Sachin Motwani 2020-8-21

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https://ww2.mathworks.cn/matlabcentral/answers/582767-why-the-image-color-bar-doesn-t-contain-certain-color-red-in-particular

编辑： Sachin Motwani 2020-8-22

I used the following code in order to explore RGB images

X = imread ('parrot.jpg');
image(X);
colorbar

The output

Why doesn't the color bar contain red color even when the image does?

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Answer 1

Image Analyst 2020-8-22

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https://ww2.mathworks.cn/matlabcentral/answers/582767-why-the-image-color-bar-doesn-t-contain-certain-color-red-in-particular#answer_483368

在 MATLAB Online 中打开

If you want to see the 3-D color gamut, you can use colorcloud

colorcloud(rgbImage);

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Sachin Motwani 2020-8-22

编辑：Sachin Motwani 2020-8-22

Thanks. This is what I wanted to see.

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Answer 2

Walter Roberson 2020-8-21

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https://ww2.mathworks.cn/matlabcentral/answers/582767-why-the-image-color-bar-doesn-t-contain-certain-color-red-in-particular#answer_483203

编辑：Walter Roberson 2020-8-22

image() never changes the active colormap. (imshow() on the other hand changes the colormap for 2d arrays but not for rgb arrays.) You were displaying an rgb image so it had no need for a colormap.

colorbar never analyzes the contents of the display. colorbar only ever puts up a copy of the current colormap and associated numeric scale. In this case the default parula map was displayed.

See also https://www.mathworks.com/help/matlab/creating_plots/color-analysis-with-bivariate-histogram.html

Image Analyst has a better analysis tool but I cannot find it at the moment.