Image processing help. Regarding pixel values and not needing to click on diagram to select pixel.

From what I understand, matlab mostly requires us to click on an image and then it will display the resulting pixel RGB value. Is there a way to let the code run through, finding ALL pixel's individual values without having to click? I do not want to select because I want to iterate through the whole picture.

How do I use code to get just R,G and B respectively of a pixel? Like when a pixel is selected, what code will give only R portion of RGB. I wish to compile RGB together meaning adding R, G and B to get my resulting pixel value.

Please help. Thanks.

Answer 1

[Image Analyst]

You can read in an image file with imread(). That will get you ALL the image pixel values without having to click on anything.

rgbImage = imread(fullFileName);

To split apart an RGB image into the individual color channels, you can do this:

% Extract the individual red, green, and blue color channels.
redChannel = rgbImage(:, :, 1);
greenChannel = rgbImage(:, :, 2);
blueChannel = rgbImage(:, :, 3);

To recombine them into an RGB image again, do this:

% Recombine separate color channels into a single, true color RGB image.
rgbImage = cat(3, redChannel, greenChannel, blueChannel);

[lim -]

Ok. So what if I want to get pixel value for say (123,123) of the image, how do i extract out the value?

[Image Analyst]

rgbValue = impixel(123, 123);

Or to get the green channel only, and if it's an RGB image, use 2 as the third index

greenValue = rgbImage(123, 123, 2);

Be careful not to confuse x,y with row,column like most people do You want rgbImage(y,x,color), NOT rgbImage(x,y,color).

[lim -]

Thank you. This has helped me alot. One last question not really related. My array declared saturates at 255. How do I change it so that the cap of each number is not at 255 but more? eg. array = zeros([765,1,1,1]); Declared like this but how to change it? My array is size 765 by 1. Thats not the important part but I want each number to be able to hold value larger than 255.

[Image Analyst]

You can cast the array to double or uint16.

array16 = zeros(rows, columns, 'uint16'); % Max is 65535
arrayDouble = zeros(rows, columns); % Max is realmax('double')

>> realmax('double')
ans =
     1.79769313486232e+308
>> intmax('uint16')
ans =
  65535

If that answers your question, can you mark it as "Accepted"?

[lim -]

Somehow when I printed out the values, array element is still capped at 255. RED, BLUE, and GREEN all prints out correct values but total_Value caps at 255. Why is this so? This is part of the code:

    for y = 1:inputB
        disp(['Image is now at [', num2str(x), ',', num2str(y),']']);
        RED = I(y, x, 1) + 1;       
        GREEN = I(y, x, 2);
        BLUE = I(y, x, 3);
        total_Value = RED + GREEN + BLUE;        
        disp(['Ans is [', num2str(RED),',', num2str(GREEN),',',num2str(BLUE),',', num2str(total_Value), ']']);        
        array(total_Value) = array(total_Value) + 1;        
    end

[Image Analyst]

They must be uint8. What does this reveal if you put it right before the second disp():

whos I
whos RED
whos GREEN
whos BLUE
whos total_value
whos array

Try casting to uint16 before summing.

total_Value = uint16(RED) + uint16(GREEN) + uint16(BLUE);

[lim -]

Oh it works now. The problem was that I did not cast it to uint16 before summing. Just adding the "total_Value = uint16(RED) + uint16(GREEN) + uint16(BLUE);" line and it works like I wanted. Thank you.