[lbotos]

I assume you've learned this from somewhere in the bowels of the photoshop documentation or years of domain knowledge? I ask because as a photoshop user of 5 years I've always wanted to learn a LOT more about the nitty gritty details (I am on hackernews :P) of what I was exporting but I didn't find a solid end-all be-all resource. Any ideas where I can find one?

[ck2]

I rarely use photoshop myself - I learned it from having to support photoshop users and solve why the images they upload to the CMS system were so massive, ie. 400k for a 600x600 photo

What we did for the non-tech people was simply tell them to always use setting #6 on photoshop and use the progressive setting. Two steps seemed the most they could handle.

http://i.imgur.com/vct3D.png (best one-shot photoshop settings for web jpegs)

I had to go into photoshop and save the same image repeatedly under all the different settings and then examine the resulting jpeg under different tools to see exactly what it was doing.

It also doesn't help that photoshop bloats jpegs by adding hidden adobe meta to every jpeg (beyond and different from exif).

Here is a technical analysis someone did on the photoshop settings:

http://www.impulseadventure.com/photo/jpeg-quantization.html...

[sirn]

>It also doesn't help that photoshop bloats jpegs by adding hidden adobe meta to every jpeg (beyond and different from exif).

I believe if you use "Save for Web", it will strip out most metadata and EXIF from the image before saving. Here's a result of using "Save for Web" (1.jpg), passing through JPEGTRAN with `-copy none -optimize` (2.jpg) and `JFIFREMOVE` (3.jpg):

    330090  1.jpg
    329916  2.jpg
    329898  3.jpg

[ck2]

Yup, jpegtran is a must for post-processing adobe images.

It can also do a lossless conversion to progressive format.

Most people do not know about it though. JPEGOPTIM is another one.

You can examine what's embedded in the image here http://regex.info/exif.cgi

but there are better offline tools.

[radley]

I don't get it. Why is jpegtran a must?

[CWIZO]

Because it strips any meta information contained in the file which reduces file size. It can also losslessly optimize the image. See here for details (I've written about it a short while ago): http://hancic.info/optimize-jpg-or-jpeg-images-automatically...

[radley]

It sounds great in theory but the previous example only saved < 200 bytes. That's not really optimization, that's overkill.

[jseliger]

In response to Radley, who said:

* It sounds great in theory but the previous example only saved < 200 bytes. That's not really optimization, that's overkill.*

That's a fair point, but if you've got a site that's getting hundreds of thousands or millions of views, or a large number of thumbnails, the one-time effort to shrink image size might be worth it.

[sandGorgon]

how does this translate into something like ImageMagick ? I mean, if I have users uploading large (>10mb) images which I want to transform into web-optimized images, is there a server-side pipeline that would give the most meaningful results ?

[radley]

The extra weight is for library management features (color, compatibility, previews, Bridge).

Web designers don't "Save" web images, they use "Save for Web" which strips out the extras.

[zurn]

Aha, the web page talks about "chroma subsampling", makes sense now. So saving less chroma than luma (color vs intensity) information.