QTR-Quadtone RIP

I'm beginning to think this whole thread has been meandering too long and too widely and too vaguely to

really help people understand what's happening with CM and what to do.

But ICC color management is an important and interesting subject. You have to understand a fair amount

of the background and general idea of it all though before you can "get it". Treating it as a magic black box

is fine for most people, but not good enough if you get into the nitty-gritty and want to understand all the

underlying processing going on.

On Sat, Jul 30, 2016 at 7:36 PM, brian_downunda@... [QuadtoneRIP] <QuadtoneRIP@yahoogroups.com> wrote:

It is my understanding that Adobe has changed the colour management in recent versions of Photoshop in a way that also affects Windows users. This change is not that well known, and fortunately for this forum, it doesn't affect QTR printing on Windows.

If you print direct from PS and select "printer manages colour" in the PS print dialog, then you will get a silent profile conversion to sRGB en route to the printer driver. This behaviour is spelt out and defended by Adobe engineer Dave Polaschek in the comments section of this article on TOP:
http://theonlinephotographer.typepad.com/the_online_photographer/2015/10/photoshop-vs-printer-managed-color-printing.html

Interesting article plus the Luminous Landscape article that is linked to in one of the comments. Trouble is: it's more

indicative of mis-information and confusion there is trying to talk about it than helpful information. Yes, there's a lot

of factual stuff in it but it's continuously interspersed with vagueness that makes it very hard to decide what's what.

My first impression about article itself: it's by a guy Ctein who is a long time photo expert from way back. Sometimes

highly respected but sometimes controversial at least in some peoples' opinions -- I don't really know. But he has

done lots in the analog world and now in the digital world. He's explicit right up front that he's talking about

printing in OS X with Photoshop and Printer Manages Color. Quote -- "What I'm recommending only works under Mac OS"
Strange thing is that with Photoshop and Printer Manages Color a very important dialog page Color Matching is

never mentioned in article or in any of the numerous comments. Neither are selections in Epson dialog settings. ??

I'm interested but skeptical about his finding -- but without more explicit info I'm not sure what can be said.

The comments wander all over -- Mac to Windows, sRGB to AdobeRGB to ProPhoto, conversions & assignments,

and particularly No Color Management (LULA article is especially about that). So it's hard to tell which

assumptions each commenter is making.

He also discusses the behaviour in OS X. This is the only place I know where an Adobe engineer has discussed this issue publicly, although be warned you will need to read his comments (there are several comment blocks from him) many times to understand fully.

My reading of his post seemed all about Windows not Mac but there's a lot of other product jargon that I'm

not familiar with. I think his most revealing quote was (his bold emphasis!):

But if you want no color management at all, you really should be printing from Photoshop CS3

or earlier where that option is explicitly available ...

I did a lot of recommending CS3 in the past but for an Adobe guy to actually saying that less than a year ago

about 6 versions of Photoshop later says a lot about how messy most of this is.

(btw, Adobe has a program called ACPU for both Mac & Windows

that is recommended for printing targets etc with No Color Management. But it9;s very limited in flexibility.)

On Sun, Jul 31, 2016 at 7:57 AM, Le Mois de la Photo à Uqbar info@moisdelaphoto.ca [QuadtoneRIP] <QuadtoneRIP@yahoogroups.com> wrote:

Roy and Brian,

You’re freaking me out! I think I’m getting answers here to questions I didn’t even realise I should be asking. That would explain perfectly what I have been describing as strange relative table behaviour.

Freaking out is not that unusual with this :)

On Sun, Jul 31, 2016 at 9:38 AM, Le Mois de la Photo à Uqbar info@... [QuadtoneRIP] <QuadtoneRIP@yahoogroups.com> wrote:

...

I can see why colour printers are concerned about this, but I’m not sure we should be. Assigning a profile can change values but converting ( using relative rendering which I’m pretty sure is the default rendering for Photoshop ) cannot, unless the values are out of gamut and since both spaces go from L*0 to L*100 my feeling is values can’t change ( you can test this in Photoshop by bouncing back and forth from Adobe to sRGB you shouldn’t see a change in lightness values , but if you assign sRGB you will).

So, I started reading the above paragraph -- "Assigning a profile can change values but converting ... cannot".

My first reaction was -- Wow, you got this all backwards! I'm guessing you do know what you are

talking about, but what about a reader?. The issue is just saying "values" -- all image files have two

kind of values -- first, the numbers in the file i.e K or RGB values, and second, the meanings of those numbers i.e.

the L* or LAB values which are derived from numbers (K or RGB) with the ICC profile attached or assumed.

This is like taking a ruler and measuring the length of something. If I tell you it 6 long you have the number but

the meaning doesn't show up until I tell whether it's inches or cm or miles. So 6 is like the RGB value, inches

is like GG2.2, and together you know the actual length which is like L-value.

Assign Profile always preserves the numbers (K or RGB) at the expense of changing L-values.

Convert Profile always tries to preserve L-values by changing the K or RGB values.

This ought to be totally ingrained in anyone trying to talk about CM but any hint that it's vague

in someone's mind throws off the whole discussion.

So my point is that any comment, question, statement that is vague about "values", vague about OS type,

vague about converting what to what, vague about anything in a workflow, becomes mostly meaningless.

Sure people will answer but you never know what assumptions they are making either.

Eugene, this is just an illustration, not you. This issue is everywhere. The link articles with all the "experts" are

riddled with vagueness. To me it just becomes impossible to get anywhere.

Roy

--

Roy Harrington
roy@...
www.harrington.com