Step 2 – Selecting the Output File Type and Quality

Pictures can be compressed in one of two ways, either with no loss at all of the original quality, or with a degree of ‘accepted’ loss of quality in favour of smaller file sizes.

PNG is a ‘lossless’ compression method, which means every tiny detail of the original image is preserved. Since this method works best when there are large areas of identical colouring (such as on a cartoon), it is rarely used for photographs on the web, since the preservation of such fine detail is often unnecessary.

JPG is a ‘lossy’ compression method, which means that fine-detail is sacrificed in areas of ‘similar’ colours, in order to reduce the overall file size. Just how much detail to sacrifice is up to you, and when selecting JPG files, this slider control becomes active. Place the mouse cursor on the vertical bar, hold down the left button and sweep the mouse left or right to control quality. The farther to the right, the more detail is left in the image but the larger the filesize will be. For most purposes, 1 or 2 notches from the right-hand edge should give excellent results.

In addition to the image type, you can also set a ‘maximum limit’ for how many pixels (picture-dots) the image is allowed to contain. Anything above this limit will be automatically resized to meet it, whereas anything below the limit will be left as-is. As a general rule, the lower the limit, the lower the size of the output file, and for the vast majority of purposes, 800x600 should be fine.