file sizes vary

[billz]

A friend asked me a question today that I couldn't answer (not unusual:)) but I thought I'd ask some of you.

He took 300 photos, same day, same camera (xti), same settings, jpg's .. not RAW, but file sizes range from 2.8 to 4.3 mb.

Any ideas?? Thanks.

Bill

[LeeOtsubo]

A friend asked me a question today that I couldn't answer (not unusual:)) but I thought I'd ask some of you.

He took 300 photos, same day, same camera (xti), same settings, jpg's .. not RAW, but file sizes range from 2.8 to 4.3 mb.

Any ideas?? Thanks.

Bill

This is a common curiousity for new digital photographers. JPEG compression is content dependent. If you were to take a photo of a flat, white surface with no texture, the file would be very small because the algorithm can compress it much more tightly. If you then took a photo of a busy scene with lots of colors, shapes, textures, shades, etc, the file would be much larger because the algorithm wouldn't be able to compress it as much.

Very simply put, JPEG looks at a pixel and determines how many other pixels around it are "similar". It then combines all the similar pixels into one pixel. Obviously there's much more to it then that but that's the gist of how JPEG works. HTH.

[billz]

Thanks Lee ... we were speculating along those lines but not at all sure.

Bill

[LeeOtsubo]

Now, try taking a JPEG photo of a flat, white surface at ISO 100 and ISO 800. The ISO 800 file will be larger because of the noise.