Digital Image Basics for non-Photographers • Blaise Tobia

The most common and most universal image file type is the JPEG (or JPG).

It carries full image resolution and color information and allows for file compression.
Compressed files take up less storage space and they transfer across networks more quickly.

But, in compressing images, the JPEG format loses some image data.
Severe JPEG compression may compromise sharpness and may create image artifacts (such as grouped squares of pixels)
although these generally don't occur with moderate compression.
Adobe JPEG Quality 12 involves the least compression and therefore maintains the most quality.
Adobe JPEG Quality 0 involves the most compression and therefore loses the most quality.

These two images demonstrate JPEG image quality varied by amount of compression:


above: section of image from file saved as JPEG Q12 (file size: 373 Kb)...below: saved as JPEG Q0 (file size: 180Kb)...


JPEG stands for Joint Picture Experts Group - who make judgements about compression, file quality, etc. in setting standards for the JPEG file format.