Re: [Gimp-user] Color mismatch when an image is printed

[Pat David]

That is, check with the printer first to see what they want.
On Fri, Sep 23, 2016 at 8:37 PM Pat David  wrote:

> Don't send CMYK to a photo print shop unless they specifically ask for it.
> The majority of high end US print shops want sRGB for photo prints (not
> books or offset printing - in that case I'd let them do the conversion
> unless you know what you're doing).
> On Fri, Sep 23, 2016 at 8:35 PM Rick Strong  wrote:
>
>> I would start by buying a monitor colour calibration device like a SPYDER
>> regardless of who is doing the printing, yourself at home or a print shop.
>> Google SPYDER. It's simple to use, fast and accurate. There are others.
>>
>> If you are sending files out to a print shop send CMYK images in North
>> America. The preference in Europe I think is LAB. Check with your printer.
>> Try the US Sheetfed/un-coated profile at home or anything that matches
>> your
>> paper and gets you close to your calibrated monitor image.
>>
>> Rick S.
>>
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Re: [Gimp-user] Color mismatch when an image is printed

[Rick Strong]

I would start by buying a monitor colour calibration device like a SPYDER 
regardless of who is doing the printing, yourself at home or a print shop. 
Google SPYDER. It's simple to use, fast and accurate. There are others.


If you are sending files out to a print shop send CMYK images in North 
America. The preference in Europe I think is LAB. Check with your printer. 
Try the US Sheetfed/un-coated profile at home or anything that matches your 
paper and gets you close to your calibrated monitor image.


Rick S. 


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Re: [Gimp-user] Color mismatch when an image is printed

[Jan Kandziora]

Am 23.09.2016 um 23:28 schrieb Pat David:
> 
>>   I have some standard ICC profiles:
>> CMYK:
>>   un-/coated
>>   web un-/coated
>>   US web un-/coated
>>   US sheetfed un-/coated
>>
>>   Would any of those be an appropriate default?
>>
> 
> Maybe?  I doubt they would be any better than any other profile that isn't
> generated from your printer and created by you.
> 
A cheap home/office printer wouldn't match any premanufactured color
profile. Maybe there is one supplied with the printer (check the
manufacturer's website) but that one is only valid when used with the
overpriced ink cartridges from the manufacturer.

So you have to calibrate your printer by hand. I wouldn't bother to
create a full profile myself but instead, do a few test prints and see
if they are okay. The ink isn't color-stable enough over years anyway.


But you should to calibrate your monitor in any case so your test prints
match a common standard instead of an arbitrary non-calibrated monitor.

Kind regards

Jan


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Re: [Gimp-user] Error in opening psd files

[Steve Kinney]

On 09/23/2016 11:57 AM, Ross Martinek wrote:

> Thanks for jogging my memory. I think what I was thinking is that Adobe had 
> color palettes based on those catalogs, intended to produce printed colors 
> that matched the catalog. Like I said, it’s been a long time.

Those catalogs would be Pantone ones.  They are usually most relevant
when printing vector graphics, i.e. silk screen or offset printing.
Printer's inks have Pantone values printed on their labels, and very
precisely match the color chips on Pantone reference cards.  I have seen
"Pantone to HTML color" charts on the network, and they are better than
nothing but far from precise.  "HTML color" means hexadecimal RGB, which
is also the GIMP's native color model.

RGB stands for Red, Green and Blue.  It is an "additive" color model,
applicable to mixing colored light sources.  Example:  TV screens and
computer monitors.

LAB stands for Luminance, Red/Green, Blue/Yellow.  It is based on
studies of human color perception and is more or less universal, but no
monitor or printer can duplicate this color space directly - it has to
be exported to RGB (monitor) or CMYK (printer) for display.

CMYK stands for Cyan, Magenta, Yellow and Black.  It is a "subtractive"
color model, applicable to mixing ink or paint colors to control the
color of reflected light.

When people start talking about computer programs that can "natively
edit in CMYK", try not to groan:  The only way to edit images in CMYK is
with a paintbrush or comparable tool, because on a monitor you see the
image in RGB no matter what format the program is reading from and
writing to.

An RGB image can be exported to or imported from a file with CMYK data,
via a filter based on the intersection of RGB and CMYK values in LAB
color space.  But "what you see" on the monitor is not exactly "what you
get" on the printed page.  Upcoming versions of the GIMP with GEGL under
the hood will support /much/ higher resolution RGB color, improving the
potential color match between screen and paper versions of a given
image.  (GIMP layers can also include an Alpha channel for transparency;
hence "RGBA" values.)

In recent times I have had no problems with color management for print;
PNG files imported to Scribus and saved as PDF come out looking like I
want them to when printed.  A decade ago, this was not always the case.
I believe that LCD monitors and improvements in color conversion
algorithms probably account for this.

To get the best available color rendering, first check your monitor.  If
a color profile is available from the manufacturer, get it and install
it on your workstation machine, and make sure the GIMP knows about it:
Edit > Preferences > Color Management.  This will tweak your video
output for "best results."  An alternative to this is to glovally
disable color management and tweak your monitor by hand, see:

http://www.lagom.nl/lcd-test/

Color perception is also a factor:  The more neutral gray you see around
an image, the less your eye and brain will distort the colors in the
image.  Conversely, if you know that a bunch of images you are working
on will be displayed on a colored background - say a web page or
brochure - you can set the Canvas Padding color in the GIMP to that
color, and see your images in progress in their native color context:
Edit > Preferences > Image Windows > Appearance.

The GIMP includes a filter that converts the visible image to CMYK
layers, and the result can be exported as a CMYK TIFF file.  This may
facilitate color adjustment at the print shop, and any commercial
printers who still demand "Adobe Formats Only, or take your filthy money
elsewhere!" will usually accept CMYK TIFF files without complaint.

Color printing used to be a bit of a major nuisance, but lately not so
much - depending the use case, your mileage may vary.  The remaining
problem is color resolution:  If you have a big, subtle gradient you
have to get just exactly right, you are going to see banding on your
monitor and in the printed results.  The upcoming GEGL based GIMP color
model, with resolutions up to 64 bit floating point, should put a stop
to that nonsense.

:o)



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Re: [Gimp-user] Color mismatch when an image is printed

[Pat David]

Hi James!

On Fri, Sep 23, 2016 at 2:59 PM James Moe  wrote:

> On 09/22/2016 09:13 AM, Pat David wrote:
> > Did you also generate a profile for your printer?
> >
>   How do I do that?
>   I'd search the online manual, except... There is no search function!
> Thus rendering the manual somewhat useless for finding specific topics.
>

http://imgur.com/a/mnhLn

The problem as I understand it (there are far smarter folks than I for
color management stuff here) is that we are talking mainly about a problem
of degrees.  Your uncalibrated monitor may or may not show you colors that
are representative of what they should be for a given colorspace.  So far
it may _seem_ ok to you, but the best you can hope for w/o calibrating or
profiling is that it looks close enough for you.  Apparently the "close
enough" has drifted recently for any number of reasons.

Pascal has a still relevant tutorial on display color profiling in linux:
https://encrypted.pcode.nl/blog/2013/11/24/display-color-profiling-on-linux/

If you have the hardware, you can use displaycal to do the calibration and
profiling: http://displaycal.net/

Basically, this will get you a profile for your monitor and hardware to
show you the correct colors.  At that stage you can be reasonably
comfortable that what you see on your calibrated hardware should look the
same on someone elses calibrated hardware (or at least really close).

The next problem is that you will need to print a reference target on your
printer, with your inks, and then use that reference print to generate a
profile for your printer.  This will allow you to use the profile for
soft-proofing your images prior to printing so that you can see what they
should look like when printed.  This is beyond the scope of a quick email,
but I'm hoping some folks on the list might have some better references to
post for you to follow...


>   I have some standard ICC profiles:
> CMYK:
>   un-/coated
>   web un-/coated
>   US web un-/coated
>   US sheetfed un-/coated
>
>   Would any of those be an appropriate default?
>

Maybe?  I doubt they would be any better than any other profile that isn't
generated from your printer and created by you.

pat
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Re: [Gimp-user] Error in opening psd files

[Ross Martinek]

Thanks for jogging my memory. I think what I was thinking is that Adobe had 
color palettes based on those catalogs, intended to produce printed colors that 
matched the catalog. Like I said, it’s been a long time.

Ross


> On Sep 23, 2016, at 10:21 AM, Alexandre Prokoudine 
>  wrote:
> 
> On Fri, Sep 23, 2016 at 5:56 PM, Ross Martinek wrote:
> 
>> Sorry my memory of it is no better. It was at least two decades ago
>> that I last had to deal much with different color standards. Steve Kinney
>> posted that PS uses LAB, which fits my memories, but I seem to recall
>> there were one or two others available, at least for printing.
> 
> You were probably referring to Pantone and Hexachrome. None of those
> spot color catalogs are related to Adobe. None of them are color
> models :)
> 
> Alex
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Re: [Gimp-user] Error in opening psd files

[Alexandre Prokoudine]

On Fri, Sep 23, 2016 at 5:56 PM, Ross Martinek wrote:

> Sorry my memory of it is no better. It was at least two decades ago
> that I last had to deal much with different color standards. Steve Kinney
> posted that PS uses LAB, which fits my memories, but I seem to recall
> there were one or two others available, at least for printing.

You were probably referring to Pantone and Hexachrome. None of those
spot color catalogs are related to Adobe. None of them are color
models :)

Alex
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Re: [Gimp-user] Error in opening psd files

[Ross Martinek]

No longer have a copy of Photoshop—I just remember the manual talking about it, 
and that they seemed to have several different color standards available.

Sorry my memory of it is no better. It was at least two decades ago that I last 
had to deal much with different color standards. Steve Kinney posted that PS 
uses LAB, which fits my memories, but I seem to recall there were one or two 
others available, at least for printing.

And regardless of whether you use RGB or LAB, printing will be CYMK. IIRC (and 
I may not) LAB is closer to CYMK.

Ross


> On Sep 23, 2016, at 4:03 AM, Alexandre Prokoudine 
>  wrote:
> 
> On Wed, Sep 21, 2016 at 2:01 AM, Ross Martinek wrote:
>> PS has a number of different color standards (some Adobe’s proprietary 
>> materials)
> 
> Any examples?
> 
> Alex
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Re: [Gimp-user] Error in opening psd files

[Partha Bagchi]

On Fri, Sep 23, 2016 at 5:03 AM, Alexandre Prokoudine <
alexandre.prokoud...@gmail.com> wrote:

> On Wed, Sep 21, 2016 at 2:01 AM, Ross Martinek wrote:
> > PS has a number of different color standards (some Adobe’s proprietary
> materials)
>
> Any examples?
>
> Alex
>
> What's a color standard? Do you mean ICC profiles? What's proprietary
material here?
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Re: [Gimp-user] Error in opening psd files

[Alexandre Prokoudine]

On Wed, Sep 21, 2016 at 2:01 AM, Ross Martinek wrote:
> PS has a number of different color standards (some Adobe’s proprietary 
> materials)

Any examples?

Alex
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