Be lossless when possible

[drrlvn]

For JPEG for example, the command jpegtran is able to losslessly perform several operations like flip, rotate by a multiple of 90 degrees and others. From its man page:

jpegtran works by rearranging the compressed data (DCT coefficients), without ever fully decoding the image. Therefore, its transformations are lossless: there is no image degradation at all, which would not be true if you used djpeg followed by cjpeg to accomplish the same conversion.

[jarun]

We do our best with what Pillow supports:

• ANTIALIAS for all operations
• option --quality