From: Daniel Piechnick
Hi Darryl. I almost always use jpeg file format, as it has better file optimisation. Jpeg files are much better for saving complicated images such as photographs, as the jpeg format works by using slightly inaccurate gradients. These inaccuracies are almost undetectable to the eye. Gif files save the image as patches of a single colour. This is excellent for diagrams or other simple images, but not for photos. Gif is limited to 256 colours. When I'm saving images in Photoshop, I usually use jpeg, Quality 60.
