jpg subsampling

Summary:

power to the user - allow us to choose what subsampling we want

jpg subsampling

DrSlony 24 Apr 2009 21:49

I need 1x1 1x1 1x1 jpeg subsampling, and it seems its currently impossible to set this myself, the power was taken away from the user and the choice was made for him, using the worst setting possible - 2x2 1x1 1x1

Here are samples saved using:
1x1 1x1 1x1
http://imgbin.org/images/461.jpg

2x1 1x1 1x1
http://imgbin.org/images/462.jpg

1x2 1x1 1x1
http://imgbin.org/images/463.jpg

2x2 1x1 1x1
http://imgbin.org/images/464.jpg

Last edited on 24 Apr 2009 23:29 by DrSlony Show more

Re: jpg subsampling

nEJC 30 Apr 2009 12:34

Disclaimer: I am not a Phatch developer - just a big fan, so some stuff herein could be wrong

The "power" was not taken, but it will most probably be given sooner or later.

Phatch uses Python Imaging Library for its image handling, and subsampling support is not yet possible in latest stable release (1.1.6).
But it appears its comming in next release … so stay tuned. Adding another dropdown menu should be almost trivial in Phatch code…

Also to note - the examples given are not what jpeg was intented to be used for - you should probably be using bitmaps for images like that (PNG perhaps?)

Wondering: what is the file size comparison of JPEG photo if you use 1x1x1 jpeg subsampling compared to PNG with maximum compression (9 in GIMP)? Is it worth it?

Re: jpg subsampling

DrSlony 30 Apr 2009 14:43

Most definitely worth it! The examples I gave were obviously made to highlight this problem, but that's not to say you wont see a difference in a normal sharp photo - you will!

Example:
png compression 9: 685.1kB
jpg quality 90 no subsampling: 115.9kB

No visible difference between the two at 100% thanks to no subsampling. Even 1 pixel wide watermarks are still perfectly sharp both in luma and chroma. Which one would you host on your site? :]

Re: jpg subsampling

nEJC 01 May 2009 00:03

Thnx for info … will most definetly have to look into this subsampling thingamajiggy ;)

Re: jpg subsampling

stani 08 May 2009 15:13

As the Phatch developer I can confirm you gave the right answer. Thanks for participating on the forum!

Re: jpg subsampling

DrSlony 15 Sep 2009 05:07

Any news on subsampling support in Phatch?

Re: jpg subsampling

stani 15 Sep 2009 06:01

Unfortunately PIL 1.1.7 has not been released yet. How does imagemagick handle subsampling?