Photoshop Save as JPG vs. Image Ready Save Optimized JPG

I've been using PS for a long time (10+ years) and haven't found an

answer to this. Maybe I'm not looking hard enough?

 

Is there a difference between saving a file from the normal Photoshop

'Save as' option as a JPG versus using the 'Save Optimized as' option

using Image Ready's save dialog box?

 

I know the reasons when I should and shouldn't save as JPG, but I want

to know if PS or IR is better, less lossy, etc. I have experimented

with both options and the PS save creates a larger file (using the

maximum - PS 12 vs. IR 100% - quality in both).

I believe that the Save For Web option does 2 things:

 

1) It converts the image to sRGB

2) It removes any embedded profile, since they're never used by browsers.

 

Tim

Oh, one thing I forgot to metion is I'm not using these images on the web, but instead for printing photos using online services like Snapfish. Snapfish and others do not accept TIF files, so JPG is my choice. Just wondering if one will give me better quality or less loss.

Standard JPEG images will have better quality than those optimized in ImageReady. ImageReady also reduces the color pallette.

I don't know about the rest of you, but I find the Save For Web

terribly slow and cumbersome on my 5 year old system.

 

I can still get a very accurate 100% view previews using the

standard jpeg PS Save As. The preview will show accurately the

varying degrees of artifacts produced with different image quality

settings. Save For Web take forever to update its preview at least

on my system.

"Save for WEB" doesn't 1) Convert the image to sRGB. 2) Remove an embedded

profile.<br>Windows browsers use sRGB, most Macintosh browsers use Apple RGB color

space. Safari is the only browser that supports embedded color profiles.

SaveAsJpeg quality 12 produces much higher image quality, with 4:4:4

chroma subsampling, than SaveForWeb 100%, which uses 4:1:1 chroma

subsampling even at the highest quality levels (this is ultra stupid).

You can set SaveAsJpeg quality down to 7 and still get 4:4:4 chroma subsampling, which seems important for thumbnails. Larger images can

go Q 6 and below to save space if you want. If you don't care about

JPEG quality, SaveForWeb might be useful to save space, I suppose.

 

Note that Apache HTTP packets are 8000 bytes maximum, so there is

little reason to go much smaller than that.

I just did some tests in Photoshop CS2 and it appears that "Save for web" is using 4:4:4

sub-sampling for anything at "medium" quality and above, assuming that ImageMagick's

identify command is correctly reporting the "JPEG-Sampling-factors" correctly.

 

At any rate, I can't see any difference in a 600x400 images between the "Save for web" and

regular "Save As". Perhaps it treats small thumbnails differently -- I didn't test that.

 

I also don't understand the relevancy of Apache's internal packet size, either. Ignoring the

fact that not everyone uses Apache (including this site) I don't see how it makes much

difference since the TCP socket the server dumps it's data stream into is going to chop it

into IP packets anyway. There may very well be slight performance advantages by

optimizing your file sizes to closely align to the internal data structures your web server

uses. But, IMHO, it's just not practical and akin to maximizing your car's fuel economy by

only driving on days where you have a tail wind.

Must be an improvement in CS2. I'll double-check using jpegdump when

CS2 arrives later this week. The admonition about 8 KB packet size

was intended for people who have their own website. What I'm saying

is there's no point making thumbnails far < 8 KB because they require

one packet anyhow.

Well, I do run a few websites.

 

I did a test with three small images; 850 bytes, 7405 bytes, and 14851 bytes. Serving from

Apache and testing with the ab utility each image transfered their size + 256 bytes

regardless of filesize. No padding. From what I can see there's still an advantage in making

thumbnails as small as possible if you're trying to keep bandwidth and server load down.

Does anyone has an idea how Aperture works on this? I would like to use Aperture to export

my webimages - problem is that if I use export image - the file size is twice as much as if

saved as webgallery. Is there any way to get around that?