Re: Do we convert soft proof when converting to profile?
Re: Do we convert soft proof when converting to profile?
- Subject: Re: Do we convert soft proof when converting to profile?
- From: Marco Ugolini <email@hidden>
- Date: Thu, 19 Feb 2009 13:00:27 -0800
- Thread-topic: Do we convert soft proof when converting to profile?
In a message dated 2/19/09 9:38 AM, John wrote:
> Thanks to a client's questions regarding our recommended CM work flow, I
> was poking around the Adobe site's color management section and found
> some contradictory information.
>
> http://help.adobe.com/en_US/Photoshop/11.0/WS03037539-15A8-4250-BC64-30247EC7A
> FB6.html
>
> "A.
> Document is created in its working color space.
>
> B.
> Document¹s color values are translated to color space of chosen proof
> profile (usually the output device¹s profile).
>
> C.
> Monitor displays proof profile¹s interpretation of document¹s color values."
>
> This appears to say that the soft proof feature presents an
> approximation of how the file will be printed if sent to the device.
Yes, hopefully a close approximation, depending on how well the monitor is
calibrated and profiled, how wide its gamut, how good its overall
performance (including a decent viewing angle, good blacks, good neutrals,
etc.), and how dependable the output profile's B2A tables are (the ones that
describe how the source file's colors are transformed from their Lab
equivalents to output CMYK, if we are soft-proofing a given press output).
> This leads me to believe that the use of a profile for soft proofing
> would guide the user to make corrections to the file based on the
> characteristics of the output device. and not need to be converted to
> profile.
No *actual* conversion takes place during soft-proofing. The source file
remains in its "native" state (RGB or CMYK, with whatever profile is
assigned to it).
Soft-proofing only shows you a *preview* of what would happen *if* you
converted the source file to the output profile, using a chosen rendering
intent, with black point compensation off or on.
> Example:
> Printer prints +5 G
> User sees this on sofproof and adds +5M to balance.
I don't look at it that way. I look at soft-proofing as being more visual
than strictly mathematical. That's why it's important to use the best tools
available, in this case a dependable monitor, well-calibrated and carefully
profiled -- because you use your eyes to make judgments that affect the way
the image will look on output. (So, don't forget to be checked for any color
vision problems you yourself may have. Various degrees and types of color
blindness are more common among men.)
Also, how do you add +5M if your source image, say, is in AdobeRGB? You
could use a Selective Color adjustment layer, but it's *not* exactly the
same as adding or subtracting Magenta *after* the file is converted to CMYK.
If a file is in AdobeRGB, it stays in AdobeRGB during the whole
soft-proofing process.
Succinctly put, that's the whole point of soft-proofing: *to preview the
results without having to convert in advance*. In other words, soft-proofing
is a tool of late-binding (converting only at the end of the process) as
opposed to early binding (converting to CMYK first, then correcting the CMYK
image after it has already possibly lost a great deal of its original
qualities).
> File is sent to device and all is well.
>
> However steps 5 and six contradict this, at :
> http://help.adobe.com/en_US/Photoshop/11.0/WSD8679923-671F-4615-8E9F-CC7A57B00
> 130.html
>
> "5. (Optional) Preview colors using a soft proof.
>
> After you create a document, you can use a soft proof to preview how
> colors will look when printed or viewed on a specific device. (See About
> soft-proofing colors.)
> Note: A soft proof alone doesn¹t let you preview how overprinting will
> look when printed on an offset press. If you work with documents that
> contain overprinting, turn on Overprint Preview to accurately preview
> overprints in a soft proof. For Acrobat, the Overprint Preview option is
> automatically applied.
I think this refers to Illustrator's Overprint Preview, which, as a graphic
design production specialist myself, I can tell you is egregiously
inaccurate.
As for inks "overprinting" one another (what is also called "ink trapping"),
a good output profile accounts for those too.
> 6. Use color management when printing and saving files.
>
> Keeping the appearance of colors consistent across all of the devices in
> your workflow is the goal of color management. Leave color management
> options enabled when printing documents, saving files, and preparing
> files for online viewing. (See Printing with color management and
> Color-managing documents for online viewing.)"
>
> This appears to imply that the optional use of a soft proof preview
> would be followed up by a convert to profile. Since this is what
> photoshop is doing when printing directly to a device with color
> management options enabled.
>
> So what IS photoshop actually doing at the softproof stage?
It's transforming the source file's colors to the destination profile
on-the-fly, using the chosen rendering intent and BPC (Black Point
Compensation). None of it is an actual conversion: just a *preview* of what
the file will look like once the user chooses to convert it later on in the
process.
> Is it showing an approximation of what the print will look like if the
> file is sent to the device as is?
> Or is it showing an approximation of what to expect with the file
> converted to profile?
The latter -- but a *close* approximation.
Marco Ugolini
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