Reduce Color Depth - no effect when we save the file

[reisrf]

I am trying to reduce the size of a JPG color file 24bpp to 8bpp. I open the original file, then I select in the upper menu Image -> Decrease Color Depth -> 256 colors (8bpp). The number of colors is reduced but when I save the file with another name or overwriting, when I open the file again the number of colors is back to 24 bpp, and the file is still big. Am I missing something here? I have tried with batch conversion and the problem is the same.

[JendaLinda]

Decreasing color depth has no effect in color JPEG images. To decrease the size of JPEG file, you can either resize the image or set lower quality when saving the image.

[reisrf]

many thanks for the prompt reply. I thought I could reduce the image size decreasing the number of colors.