Thanks for the reply, haven't used Image::Compare myself before but I imagine it's probably due to bitmaps being easy to convert to arrays of pixels, which would be necessary for thresholding, whereas the other formats are compressed so it's more difficult to extract the information; I'm sure someone else can confirm this though
Comment on Re^9: Can i Compare two images in perl ?
Yes i totally agree with you, bitmap images store information in a per pixel format so comparison per pixel is done and result is evaluated. And thus it takes more time which is directly propotional to the size in pixels of the image.