Hi APE
I'de say that the png is small enough to loaded into the windows disk cash so it only loads once from the hard drive and 99 times from memory. The BMP is probabaly being loaded from the hard drive every time.
Or
The file loading routines for Png and BMP are different. To isolate the hard drive time try creating a ram disk to store the image.
Ps in real world PNG will be faster as the hard drive is far more of a bottle neck than the CPU having to process the PNG.
Thats my bit
I'de say that the png is small enough to loaded into the windows disk cash so it only loads once from the hard drive and 99 times from memory. The BMP is probabaly being loaded from the hard drive every time.
Or
The file loading routines for Png and BMP are different. To isolate the hard drive time try creating a ram disk to store the image.
Ps in real world PNG will be faster as the hard drive is far more of a bottle neck than the CPU having to process the PNG.
Thats my bit