how to find the brightness of an image?

how to find the brightness of a particular part of an image? and how to find the brightness of an entire image?

Answer 1

[Walter Roberson]

If brightness is luminance, rgb2gray() the portion of the image.

Answer 2

[Image Analyst]

How do you define brightness? Is it just the mean? How about

brightness = mean2(yourImage);

or

brightness = mean2(yourImage(row1:row2, col1:col2));

[Shaun Roberts]

Hi Image Analyst,

Based on your Video Processing Tutorial - https://uk.mathworks.com/matlabcentral/fileexchange/47726-video-processing-tutorial?s_tid=prof_contriblnk

I am looking to expand the features so I can run an analysis of low level features to see if they can be used for video recommendation.

The first one I have been looking at is Brightness mean would it be possible to work this into your current example?

[Image Analyst]

The program does compute the brightness of the gray scale version as well as each of the color channels. You can find this code in there:

		% Calculate the mean gray level.
		grayImage = rgb2gray(thisFrame);
		meanGrayLevels(frame) = mean(grayImage(:));
		
		% Calculate the mean R, G, and B levels.
		meanRedLevels(frame) = mean(mean(thisFrame(:, :, 1)));
		meanGreenLevels(frame) = mean(mean(thisFrame(:, :, 2)));
		meanBlueLevels(frame) = mean(mean(thisFrame(:, :, 3)));