what does a histogram represent of a image ?

What is the x axis and y axis in a histogram of a image. how does it work ?

Answer 1

[Image Analyst]

The x axis is the gray level (intensity, brightness) of the image. The y axis is the count of how many pixels in the image have the gray level. It's often useful to look at the histogram to figure out how to threshold the image to create a binary image of foreground and background objects so that you can do connected components labeling and measurement of various characteristics with the regionprops() function.

[Farjana Yeasmin]

thank you

[Farjana Yeasmin]

Is the ans is approved for both RGB and gray scale image ?

[Image Analyst]

Yes. Normally you'd take the histogram of each color channel separately.

% Extract the individual red, green, and blue color channels.
redChannel = rgbImage(:, :, 1);
greenChannel = rgbImage(:, :, 2);
blueChannel = rgbImage(:, :, 3);
% Now take histograms of the individual color channels.
[countsR, grayLevelsR] = imhist(redChannel);
[countsG, grayLevelsG] = imhist(greenChannel);
[countsB, grayLevelsB] = imhist(blueChannel);