Digital BW, The Print

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "odesmais" <odesmais@y...> 
wrote:
> Roy,
> 
> Thanks for the reply. 
> 
> First, I believe I can turn comma vs point probably by simply 
> swapping Colorshop X back to US vs French. If not I'll do it manually.
> 
> Where I don't follow you is on the assessing the profile is 
> acceptable. Yes the G2,2_Profil samples make a similar-to-kTRC 
> curve : this precisely is why I suspected my whole profile(ing) was 
> wrong, I was expecting a curve similar to the GMprofile one in the 
> sense of being perfectly curvilinear since the L* measures feeding 
> the droplet are in a linear description and there's no color. A mere 
> compression in my expectations should have provided the perfect curve 
> I see on the GMprofile in a kind of gamma function. 
> 
> Perceptual intent is compressing the gamut, and in our case the L* 
> only, so why isn't it a kind of (curvi)linear line and not the messy 
> one I got? 

Well the standard QTR linearization does a straightline of L values from
paper white to dmax black.  At first I thought that was the "right" way to
to scale L (0...100) to L (17...96).  But if you do this the prints always look
lighter that what you expect.  After a fair amount to reading I found that the
more correct way to scale is using the Y luminance values.  If you were to
plot the before and after Y values the scaling is linear -- i.e. straight-line.
It's hard to visualize this especially since the values are not separated evenly.
The weird shape in the L graph is not at all intuitive but the math just works 
out this way.

Has it got anyting to do with the BPC handling ?

Sort of because the linear Y scaling is exactly what PS does for BPC.

> 
> Yes G2,2 is a "dark" space, but any source space does not really 
> matter as long as you keep it as source for both prints (w/ and w/o 
> the profile)for the evaluating (as you said embedded profile does not 

The only important thing -- especially on the PC -- is you have to be very
deliberate about your Assigning and Converting profiles.  Sometimes its
explicit and sometimes implicit.

> really matter): as you can see at G2,2 the measured L* are the one I 
> get when printing just the linearised stepwedge. The "proportional" 
> effect (darkening of the print) thru the ICC was what I intended to 
> evaluate and did prove unsastisfactory (IMHO). 
> 
> Yes, I started producing one or two prints though not yet with the 
> purpose of really evaluating precisely the prints (I was just bored 
> with the spectro and all the datas...). Well as expected blocked 
> shadows... but I admit I did not edit at all (and even not for the 
> blacks). And I'd say it matched the screen, but again this is not an 
> evaluation, I did not carefully looked at the blacks and the 
> highlights...

"Matching the screen" is really the ONLY goal.  Color management doesn't
really address things such as shadow separation.  It's entirely based on profiles
that characterize the different devices and conversions to "best" (not perfect)
give the same feel of the image.

> 
> When I work color I mostly use rel/col. rendering unless I have a lot 
> of out-of-gamut colors and if needed edit one or two tones so I keep 
> the saturation (there's no harsh and arbiratory compression of the 
> source gamut). Even for KCMY (vs grey inks) B&W I was getting 
> acceptable results (albeit metamerism and dominantes with some 
> papers). Wouldn't it make (any) sense to use the same for 
> monochromatic B&W ? 

I believe that that is what you are getting -- its just that with color you can't
see what's going on behind the scenes.  If you can do a good color
profile it might be interesting to see and measure the results of a gray
stepwedge there.

> 
> I must sound like winding, but I was expecting the ICC to possibly 
> compress "evenly" the values and use it straight to print... I feel I 
> got a CM workflow but at the detriment of the grayscale smoothness.

I think you are focusing on the look of the curves too much.  You really need
to go by seeing your profiled screen and your prints.  Try it both ways and see
if you can see the difference in screen/print matching.

Roy


> 
> Anyway, you have a great soft Roy and offer a great support. If you 
> grant me additional advises they will be more than welcome.
> 
> Thanks a lot.
> 
> Olivier