Structural similarity for RGB image

I want to calculate the structural similarity between two RGB images. I was using Matlab built-in command ssim but got an error message.

Is there anything I need to do or other command for RGB image structural similarity??

My attempts and error message :

ssim(image11,a1) %% image11, a1 two RGB image. Image dimension 256x256x3
"Error using conv2
N-D arrays are not supported.
Error in filter2 (line 59)
        y = conv2(hcol, hrow, x, shape);
Error in ssim (line 188)
mu1   = filter2(window, img1, 'valid'); 

Answer 1

[vidhathri bhat]

Hi,

ssim function in matlab does not support RGB images. You will have to convert both images to greyscale image.

Answer 2

[D.Regan]

Hello,

SSIM is not intended to RGB images directly. To calculate SSIM here, convert RGB to YCbCr then follow the 0.8SSIMY + 0.1SSIMCr + 0.1SSIMCb.

For Ref:

https://arxiv.org/pdf/2006.13846.pdf

Hope this will help you better.