Question about Save for Web

I was told today that Photoshop's Save for web function reduces the number of levels of colour in a file from 256 to 216 (in jpegs) as one of the ways to reduce file size, and also to comply with the antiquated notion of "web-safe colours".

I never knew this! Can anyone confirm/deny?

Ooh, I don't know. All I do know is that it strips the exif data which is why I tend not to use it these days.

Damo77 wrote in post #5379231
I was told today that Photoshop's Save for web function reduces the number of levels of colour in a file from 256 to 216 (in jpegs) as one of the ways to reduce file size, and also to comply with the antiquated notion of "web-safe colours".

I never knew this! Can anyone confirm/deny?

Deny.
It can be set to use "web safe colors" (not for jpg images though), but doesn't do so unless told to.

how do you think JPEG works?

any JPEG compression will strip colour from the image! the amount of colour taken from the image depends on the compression setting..

what scares me the most is the quote on your website and the lack of knowledge that you possess

Whoa!

So enlighten me, Robert. I thought I was well aware how jpegs work - but I've never heard of them possessing indexed-colour-like capabilities that are found in GIFs.

I didn't think the act of JPEG compression reduced the 256 levels of colour per channel.

Bobster wrote in post #5379380
how do you think JPEG works?

any JPEG compression will strip colour from the image! the amount of colour taken from the image depends on the compression setting..

what scares me the most is the quote on your website and the lack of knowledge that you possess

Click
"The second fundamental advantage of JPEG is that it stores full color
information: 24 bits/pixel (16 million colors). GIF, the other image format
widely used on the net, can only store 8 bits/pixel (256 or fewer colors)."

Off course, you might loose some color accuracy depending on compression, but you sure don't go from 24bit to 8 bit....

Some more: Click.

René Damkot wrote in post #5379623
Off course, you might loose some color accuracy depending on compression, but you sure don't go from 24bit to 8 bit....

quite, but the OP didn't say anything about going from 24-8bit, just that you lose colour saving as a JPEG when using the Save for Web..

which will happen with any JPEG even though the file is a 24bit one, if you take your 24bit TIFF and save as a JPEG, even a lv12 in PS you will drop as much as 40% of the original colour and at the lowest as much as 96% of the original colour! (i attended a talk given by a lecturer in computer science who had written an app that counted the amount of colour that a JPG will take when compressing, i knew that you lost some of the image, but i never imagined as much as that!)

The OP mentioned "Web Safe Colors"

As to the 40%: I'd be very interested in seeing a more detailed analysis of that. Also: In how far is it visible? (ie: what colors are we talking about)

I know I do *not* see any difference between a tiff and a lv 12 jpg. (when comparing side by side at 100%). None Whatsoever. I'd imagine I'd see a 10% color loss, let alone 40%!

Bobster wrote in post #5380884
quite, but the OP didn't say anything about going from 24-8bit, just that you lose colour saving as a JPEG when using the Save for Web.

Sorry if my post was a bit ambiguous - sometimes things that sound quite clear in my head, aren't quite so clear in writing!

René Damkot wrote in post #5381001
The OP mentioned "Web Safe Colors"

Yes, that's what I meant. Thanks René.

René Damkot wrote in post #5381001
As to the 40%: I'd be very interested in seeing a more detailed analysis of that. Also: In how far is it visible? (ie: what colors are we talking about)

I'm interested in learning more about this too. Am I right in thinking that the percentage of colour loss isn't uniform across the channels? I think that the loss would be greatest in the blue channel, correct?

Bobster wrote in post #5379380
what scares me the most is the quote on your website and the lack of knowledge that you possess

Actually, I think I'm pretty handy in Photoshop, for what it's worth.

I'm sure I'm not the first person to promote themselves proudly on a website. My potential customers are using search terms like "Photoshop expert in Brisbane", so I need to be able to get a piece of that pie. I've never let anybody down yet.

Credible exaggeration is the stuff of marketing, surely? If you've ever seen an ad for a McDonalds burger, it's about three inches thick and not a drop of grease to be seen. Not exactly accurate, but it gets hungry punters through the doors.

René Damkot wrote in post #5381001
I know I do *not* see any difference between a tiff and a lv 12 jpg. (when comparing side by side at 100%). None Whatsoever. I'd imagine I'd see a 10% color loss, let alone 40%!

Damo77 wrote in post #5383254
I'm interested in learning more about this too. Am I right in thinking that the percentage of colour loss isn't uniform across the channels? I think that the loss would be greatest in the blue channel, correct?

i'm trying to find the guy to see if he has a website with the information on, all i can remember was he had a 9000x9000 document with colours in it, the app he wrote counted the colours before and after each jpg setting from the original TIFF file and the numbers were astonishing!

in order to really see differences you need to be @ 400% view i believe, even @ 12 setting the compression has to come from somewhere right

Damo77 wrote in post #5383304
I'm sure I'm not the first person to promote themselves proudly on a website. My potential customers are using search terms like "Photoshop expert in Brisbane", so I need to be able to get a piece of that pie. I've never let anybody down yet.

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