Blurring: using -progressive is much slower than baseline

[Stefal]

I noticed that displaying blurred images was much slower than unblurred images. I've noticed the same slower behaviour when loading these blurred images in Josm or The Gimp.

After some investigations, the culprit seems to be the -progressive argument used with all jpegtran command, ie:

sgblur/src/blur/blur.py

Line 118 in 16d6ae8

p = subprocess.run('jpegtran -progressive -optimize -copy all -trim -drop +%s+%s %s %s > %s' % (crop_rects[c][0], crop_rects[c][1], tmpcrop+'_tmp', tmp, tmp+'_tmp'), shell=True)

When I remove this argument, I get back the original speed, and the blurring process on large images is much faster.

Blurring 20 high res images (80MP) with -progressive : 687 seconds
Blurring 20 high res images (80MP) without -progressive : 260 seconds

This 2.6 factor depends on the image size and how many areas need to be blurred.

As Panoramax/geovisio viewer use only baseline images, and has to convert back blurred images from progressive to baseline, I propose to remove -progressive

It looks like there is one drawback : baseline images are a little bigger, about 4% on my 20 jpg set.

[Stefal]

Some discussions on baseline/progressive jpeg:
yeoman/yeoman#810 (comment)
yeoman/yeoman#810 (comment)

More space needed with baseline jpg:
https://www.bookofspeed.com/chapter5.html