When loading images with new Image(<URL>, <thumb_width>, <thumb_height>, true, true) when the source image is much bigger than the thumbnail size. We are really slow at this especially on embedded Beagle.

We used to have support for libjpeg sub-sampling for 50%, 25% etc but after some digging it was removed in a bug fix in Feb 2010 RT-7536 so we need to put this back in. It turned out the old code was incorrect because it asked libjpeg for a exact fraction when the docs say only 1/1, 1/2, 1/4 and 1/8 are supported.

I have attached a test case. Test numbers for before and after fix are:

BEAGLE 3.0

LOAD at 100% took = 3915ms
LOAD at 50% took = 8658ms
LOAD at 25% took = 6987ms
LOAD at 12.5% took = 5938ms
LOAD at 6.25% took = 5485ms
LOAD at 60x60 THUMBNAIL took = 5184ms

after fix

LOAD at 100% took = 3995ms
LOAD at 50% took = 1354ms
LOAD at 25% took = 630ms
LOAD at 12.5% took = 514ms
LOAD at 6.25% took = 590ms
LOAD at 60x60 THUMBNAIL took = 523ms

This shows a nice 8x to 10x improvement for all requested sizes 50% or less. On desktop this is only a 4x-5x but still nice.