This option is the JPEG/PNG/MIFF compression quality setting.

For the JPEG image format, quality is 0 (worst) to 100 (best). The default quality is 75.

Quality for the MIFF and PNG image format sets the amount of image compression (quality / 10) and filter-type (quality % 10). Compression quality values range from 0 (worst) to 100 (best). If filter-type is 4 or less, the specified filter-type is used for all scanlines:

    0: none
    1: sub
    2: up
    3: average
    4: Paeth

If filter-type is 5, adaptive filtering is used when quality is greater than 50 and the image does not have a color map, otherwise no filtering is used.

If filter-type is 6 or more, adaptive filtering with minimum-sum-of-absolute-values is used.

The default is quality is 75. Which means nearly the best compression with adaptive filtering.