JPEG "reencoding"? Which encoder gives best results?

[Nowhere]

I wonder which of the easily available programs capable of encoding does best job at it.
Also, I don't mean so much encoding from BMP to JPEG, but reencoding high resolution/quality setting images to lower resolution/quality setting. I imagine this can complicate things slightly... (probably negligible anyway...)
Think reencoding images made by digicam into something for mailing, 800x600 or 1024x768, as small as possible by still good looking.

[schmosef]

My understanding is that in order to render a jpeg (to a computer screen) the software has to turn it into a bitmap in memory. Any re-encoding uses that bitmap as the basis, not the original jpeg.

I suppose that some software is better than others at encoding jpegs, but the tech has been around so long, and is based on a standard that was released to the public by some industry group (remembering back to the days when I had jpeg viewers for DOS), that I expect the difference to be quite negligible, especially at resolutions like you've suggested.

Just get a converter that has a preview and a lot of options in the quality scale.

I use Corel Paint Shop Pro (used to be made by Jasc). I like it.

[Nowhere]

Well, I'd definetally like a "live" converter, with some kind of slider moving between min-max quality setting and instant preview... Is there such a thing?

[schmosef]

yeah... Corel Paint Shop Pro.

[az]

Or Corel Photo-Paint. Or some kind of image web optimizer. Or just use IrfanView and batch convert.

[Nowhere]

schmosef, where's slider?!

(also...Corel PSP?!)

[Nappe1]

schmosef, where's slider?!

(also...Corel PSP?!)

yeah, JASC sold their souls to corporate giant over a year ago.

even Adobe Photoshop has nowadays Web picture compression tool, that has 4 preview windows (for different compression settings) and slider to control compression.

[schmosef]

schmosef, where's slider?!

(also...Corel PSP?!)

Yes, it's called Corel PSP for short.

The slider appears when you click the dropdownlist icon. It goes in increments of 1 from 1 (Best Quality) to 99 (Worst Quality).

You can type in the #, use the up/down rocker buttons, or use the slider.

[Nowhere]

Uhmmm...OK, but such dropdownlists usually react only when you click mouse and in that monent dissapear. Iis it constantly present slider (you know...like volume control in windows) that reacts solely to movent, so I can see the image changing as I slide it?

[schmosef]

Uhmmm...OK, but such dropdownlists usually react only when you click mouse and in that monent dissapear. Iis it constantly present slider (you know...like volume control in windows) that reacts solely to movent, so I can see the image changing as I slide it?

Yes, you have to hold the mouse button down to keep the slider visible and yes you can see the effects of sliding to the left or right in real time. I never use the slider though, it's not precise enough for my taste. I just type in #s directly until I get close to the quality level I want, then use the rocker buttons to get the rest of the way.

[James Loudon]

Until I became a Photoshop whore I used to use Micrografx Picture Publisher which had a brilliant JPG export with as you want, a slider and live preview. It was actually streets ahead of Adobe in its time for outputting to web. Unfortunately they are no more but if you can find one cheap on ebay or for nowt its well recommended.

[Marshmallowman]

The Gimp has exactly that when saving jpeg, you click show preview and you get to play with a slider and watch the results immediatly

[Nowhere]

Hmmm...perfect. (and I seem to have read somewhere that Gimp has exceptional jpeg encoding quality?)

[Nowhere]

GIMP works really nice in doing this.


BTW, I haven't answered that:

My understanding is that in order to render a jpeg (to a computer screen) the software has to turn it into a bitmap in memory. Any re-encoding uses that bitmap as the basis, not the original jpeg.
...

Of course, but the bitmap has the same quality as original jpeg, the same artifacts and so on. My guess was that, similarly to mp3/ogg/mpc/whatever transcoding (to lower bitrate), high compression jpeg encoded from another jpeg will have worse quality than jpeg encoded from orginal bitmap aiming for the same res and size. And perhaps that there's a software/encoder/encoder options aiming to minimise this.