QTR-Quadtone RIP

Ernst,

The trouble with this whole discussion is that there are many settings
in all these programs that are left unspecified.

Take for instance this excerpt:

> that load the Qimage processed RGB file in Photoshop with CM
> off, convert to Greyscale, and it gets the same %K numbers
> again as the original converted and saved greyscale target has

Presumably the RGB file from Qimage is "untagged RGB".   If you read it
into PS its treated as if it had the RGB working space in PS Color 
Settings.
If you convert to grayscale it converts to the Gray working space.  So 
it's
impossible to draw any conclusions.  I.e. lots of CM is happening, you 
can't
get away from it.

In PS just because something says "untagged" doesn't mean that there's 
no CM
going on -- it just means that the profile being used isn't stored with 
the file.
It will be treated as the corresponding working space.

 From what I've deciphered Qimage is a bit more complicated.  It says 
input file
embedded profiles are always honored, but you can turn off Ptr ICC 
conversion
so there's nothing to convert it too.  I'm guessing this may be the one 
exception
to the "CM is always running" rule -- because somehow you have to be 
able
to go from a profiled gray input to RGB output.  I think it just sets 
R=G=B=gray input.

The only way to understand all this is break everything into individual 
steps and
understanding what each does.

Roy

On Tuesday, September 5, 2006, at 04:48  AM, Ernst Dinkla wrote:

> Roy Harrington wrote:
>> On Monday, September 4, 2006, at 02:03  PM, Ernst Dinkla wrote:
>>
>>> Roy Harrington wrote:
>>>
>>>> I think Ernst may have pinpointed the issue.
>>>
>>> Roy,
>>>
>>> I'm not so sure about that right now.  I have done this before
>>> and I think I made the same mistake again. Qimage actually
>>> does exactly the same as Photoshop does when CM is off in both
>>> applications. When CM is off in PS the Greyscale one will
>>> convert to the same RGB numbers the Qimage conversion makes
>>> when CM is off. So Qimage and Photoshop behave the same when
>>> CM is off. The plain TIFF converter of my website that has no
>>> CM at all produces the same numbers.
>>>
>>> When the Qimage Print to File RGB file is brought back into
>>> Photoshop  and converted to greyscale (with CM on) to compare
>>> it to the original that was loaded to Qimage then there's a
>>> difference but that is because the CM in Qimage was off and
>>> the CM in Photoshop was on. With CM off in Photoshop the
>>> Qimage produced RGB file will convert back to the same
>>> greyscale percentages on the steps.
>>>
>>> I guess QTR has the same conversion for RGB>Greyscale as
>>> Qimage and Photoshop have with CM off. In that case my
>>> workflow with greyscale converted to the QTR grey printer
>>> profile, then loaded in Qimage with CM off and the print to
>>> file RGB sent to QTR which converts it back to greyscale is
>>> still valid and there is no fault in Qimage.
>>>
>>> Ernst
>>>
>>
>> Photoshop doesn't really have a CM off mode when you do
>> conversions.   What you have set in Color Settings -- the working
>> spaces determines what happens.
>>
>> I'm not sure what Qimage does in these cases.
>>
>> Roy
>>
>
> Roy,
>
> Let me start from another point then. Using Photoshop to
> simulate what goes on in Qimage is tricky. I have to admit
> that. Now I just do what my B&W workflow has been so far:
>
> For this test only: I assign, with Photoshop CM on, the Gray
> Lab profile to the 21 step Greyscale target, convert the
> assigned Greyscale target to the QTR Gray Matte paper profile,
> save that file.
>
> Load that saved greyscale file in Qimage with CM off and after
> that load the Qimage processed RGB file in Photoshop with CM
> off, convert to Greyscale, and it gets the same %K numbers
> again as the original converted and saved greyscale target has
> in PS (minus or plus some 1% shifts as a result of rounding
> offs on RGB numbers). Could be that the RGB to greyscale
> conversion with CM off in PS is going along my custom monitor
> profile that pops in at the workspace line as a replacement
> for AdobeRGB when I switch CM off.
>
> Even less PS influence: If I pull the same saved greyscale
> through the RGB conversion in TIFFconvert (libTIFF based) I
> get the same RGB numbers in Photoshop as the Qimage processed
> file gives. I expect QTR to behave the same as Qimage with CM
> off or behave like the libTIFF application that knows no CM
> like QTR knows no CM. I see some references to libTIFF in
> CUPS/GIMP/LCMS docs so it may well be the same conversion in
> QTR/TIFFconvert/Qimage. Whether the greyscale to RGB
> conversion defaults to a sRGB or another space relation in all
> applications without CM doesn't matter to me anymore if the
> conversion the other way around is the same again.
>
> The test is like the way I have printed B&W with
> Photoshop>Qimage>QTR since QTR profiles became available. A
> scanned B&W file gets Gamma 2.2 assigned in Vuescan, that file
> is converted to Gray Lab in Photoshop, edited then on a
> calibrated monitor so I like the tones (soft proofing too),
> converted to Gray Matte paper profile (or the custom ones I
> made) and then brought to Qimage with CM off, processed to RGB
> and that dropped in QTR. That worked best for me and I see no
> flaw in this or it has to be the conversion from RGB to
> Greyscale in QTR that isn't transparent to me.
>
> For the time being I stick to this method as I trust Qimage's
> CM conversions on B&W files less but have not tested them lately.
>
>
> Ernst
>
>
> -- 
>
>                     --
>            Ernst Dinkla
>
-
Roy Harrington
roy@...
Black & White Photo Gallery
http://www.harrington.com