Help with reading the RGB value of every pixel of a truecolor image using impixel

Hi, I have a 16bit tiff that I want to get the RGB value from each pixel in the image. The image is a 3840x2160 16bit tiff. So, I ran the impixel command:

      I= imread('sample.tif');
      c = [1:3840,];
      r = [1:2160,];
      impixel(I,c,r)

but I get this error:

    Error using impixel>parse_inputs (line 257)
    Xi and Yi must have the same length.
    Error in impixel (line 76)
    [a,cm,xi,yi,x,y] = parse_inputs(varargin{:});
    Error in pixel_get (line 4)
    impixel(I,c,r)

Am I doing something wrong with the syntax for column or range? Or do you suggest doing this a different way?

Thanks

Answer 1

[Veda Upadhye]

Hi,

The error indicates that the vectors 'c' and 'r' should have the same length.

According to the documentation of impixel (https://www.mathworks.com/help/images/ref/impixel.html),

"impixel(I,c,r) returns the values of pixels specified by the row and column vectors r and c. r and c must be equal-length vectors. The kth row of P contains the RGB values for the pixel (r(k),c(k))."

For example, the following modification in your code would work.

I= imread('sample.tif');
c = [1:2160];
r = [1:2160];
impixel(I,c,r)

Hope this helped!

-Veda

[ChickenHunter]

Thanks for the tip Veda! I got just around the equal length requirement by running the command on each row & column of the image and then dumping the output to a file. For example for row 200:

A = imread('Sample.tif');
[r_A c_A not_used]=size(A)
r=200*ones(1,c_A)
c=[1:c_A]
T = impixel(A,c,r);dlmwrite('sample.txt', T);

I wonder if there is a better way to read each pixel value of an image. I am essentially trying to look at the pixels values of two identical images (with a slight color change) and then doing a DeltaE2000 of each pixel.

Answer 2

[Chris Loizou]

Hello,

yes well you are doing something wrong with sintax. Remove the comma from the brackets

if true
  I= imread('sample.tif');
    c = [1:3840];
    r = [1:2160];
    impixel(I,c,r)
end