when i compare a input image with a existing database image this error is shown.what should i do?

Error using rgb2gray>parse_inputs (line 72)
RGB must be a m x n x 3 array.

Error in rgb2gray (line 52)
isRGB = parse_inputs(X);

Error in main_single (line 6)
if ndims(img) == 3; img = rgb2gray(img); end  % Color Images
 

Answer 1

[Walter Roberson]

You could get that if your img is something by something by 4 or higher.

something by something by 4 can happen with imread() in some cases with RGBA images (TIFF or PNG or BMP or JP2), and with CMYK images (TIFF); https://www.mathworks.com/matlabcentral/answers/457695-how-to-know-if-image-is-rgb#answer_371591