HOW to work our light intensity of an image??

how to work out the light intensity of an image? can someone provide me sample code to show this?

Answer 1

[Walter Roberson]

An image is data. Data does not have a light intensity. Data might represent a light intensity. But you have to ask the question of whether it represents the transmitted intensity or the received intensity. And you have to ask about the relationship between the numbers in the stored data and the actual values (e.g., 3 might represent 3 millilumen, but 5 might represent 17 millilumen: the relationship is not necessarily one that is expressible in a simple equation, especially near the extremes of the possible values.)

[task_m]

i mean the contrast of light in comparison of more than one image. can you give me an example code for this please

[Image Analyst]

Your clarification is not helpful. "work out the light intensity" or "work out the light contrast" is not a precise mathematical description of an algorithm - we'd have no idea what to code up. Would you, if I asked that of you? Look at it from our viewpoint.

To process multiple images, see http://matlab.wikia.com/wiki/FAQ#How_can_I_process_a_sequence_of_files.3F

[task_m]

ok. my question currently. 1) how to work out colour intensity in an image (red blue and green spearate via using hsv values???

[Image Analyst]

I think you mean color segmentation, so see my answer.

[Walter Roberson]

What do you mean by "colour intensity" for this purpose? Are you looking for "luminance" ? "Luma" ? "brightness" ? "Lightness" ?

Are you certain that you want to calculate the "colour intensity" of each of the components R, G, B, separately? "colour intensity" in its various forms is usually a function of all three components together.

[Image Analyst]

What I guessed from his comment was that he wanted to extract out (rather than work out) all regions or pixels in the image that were red, or blue, or green, or whatever color he specifies, though I could be wrong. Of course posting an image and describing what he wants to do or measure in it would be most helpful.

[Walter Roberson]

It looked to me that s/he is being asked to figure out which images are most nearly the same "contrastiness", possibly as one step in a CBIR.

Answer 2

[Image Analyst]

See my color segmentation demos in my File Exchange where I extract out parts of the image that are a certain color: http://www.mathworks.com/matlabcentral/fileexchange/?term=authorid%3A31862

[task_m]

what i need help with 1)loop of images (5 images) 2) read the red,green,blue of the overall image (not one section and not rgb values) 3)plot it

any example??

[Walter Roberson]

http://matlab.wikia.com/wiki/FAQ#How_can_I_process_a_sequence_of_files.3F

What do you mean by the red of the overall image ?

[Image Analyst]

I suggest you have another person help you craft your question because it's taking way too long to make yourself understood. Perhaps you mean this, but I'm not sure

% Read in a standard MATLAB gray scale demo image.
myFolder = fullfile(matlabroot, '\toolbox\images\imdemos');
filePattern = fullfile(myFolder, '*.jpg');
jpegFiles = dir(filePattern);
subplot(2, 1, 1);
for k = 1:length(jpegFiles)
  baseFileName = jpegFiles(k).name;
  fullFileName = fullfile(myFolder, baseFileName);
  fprintf(1, 'Now reading %s\n', fullFileName);
  rgbImage = imread(fullFileName);
  % Display color image.
  imshow(rgbImage);  % Display image.
  drawnow; % Force display to update immediately.
  % Extract the individual red, green, and blue color channels.
  redChannel = rgbImage(:, :, 1);
  greenChannel = rgbImage(:, :, 2);
  blueChannel = rgbImage(:, :, 3);
  % Get means
  redMean(k) = mean2(redChannel);
  greenMean(k) = mean2(greenChannel);
  blueMean = mean2(blueChannel);
end
subplot(2, 1, 2);
plot(redMean, 'r-', 'LineWidth', 3);
hold on;
plot(greenMean, 'g-', 'LineWidth', 3);
plot(blueMean, 'b-', 'LineWidth', 3);