[gs-devel] PDF rasterization for driverless printing: Color Management

[Till Kamppeter]

On 21/05/2021 00:40, michael.vrhel at artifex.com wrote:
> 
> AdobeRGB has the larger gamut.  If your printer supports it, why would you not print to that color space?
> 

OK, I have already changed my code to select AdobeRGB in such a case.

>> Can one pre-check on the file if this is the case before rendering it?
>> And if yes, how?
> 
> Not at this point.  But I don't even see why you would want to check.  If they occur so infrequently, just use -dUsePDFX3Profile and if there is not an output intent, it won’t affect things.
>

OK< will simply add this argument, if there is no problem to use it 
together with -sOutputICCProfile="...".

What exactly happens if I use both? Which profile is used? And if my 
printer only supports sRGB/AdobeRGB (and I do '-dUsePDFX3Profile 
-sOutputICCProfile="a8.icm"' to select the printer's AdobeRGB) what 
happens if the PDF has its embedded profile and what if not? Are there 
any problems with output quality loss due to color conversion detours?

>> And if a printer supports sRGB with 8 and 16 bit color depth and AdobeRGB
>> with only 8 bit color depth, what to take for print-quality=high? sRGB 16-bit or
>> AdobeRGB 8-bit?
>>
> 
> Is there not an AdobeRGB 16-bit mode for this case?  If someone built a printer and it only had a sRGB 16-bit option vs an AdobeRGB 8-bit option, I would send it back.  With the larger gamut, more bits are needed in AdobeRGB not sRGB.
> 

I have checked now something like 5 or 6 printers (HP, Epson, Brother) 
from which I have the get-printer-attributes IPP responses and none of 
them falls into this category (and probably the cheapest of the bunch, 
the HP DeskJet 2540 supports both 16 bit and AdobeRGB, including 
AdobeRGB in 16 bit).

So I think I can easily assume this as non-existing. If there is 
actually such a printer, it is so rare that I will probably never get a 
complaint.

My current code first selects the best color space, simply by what the 
printer supports and whether the color profile is handy in case od 
DeviceRGB, then 8/16 bit within that color space by the print-quality 
setting.

> 
> If there is a custom or non-standard profile for a printer, you should use that.
> 

OK, so I will choose DeviceRGB if the profile is handy, otherwise 
AdobeRGB if available, otherwise sRGB.

    Till