Digital BW, The Print

>Hi Steve,
>
>I think "what's optimal"   "what gamma?" or even "why a gamma curve at all"
>ends up being somewhat of a circular argument.   I don't think anybody can
>really argue that any one way is absolutely the best.   But most of the reason
>for all this, is because for B&W the approach has been mostly a trial and
>error to match the screen and print.   So if you happened to be using gamma 1.8
>for your file you have one notion of what "middle gray" is but if you use
>gamma 2.2 you have a different notion (middle gray is darker).  You then
>tweaked the output method to match your notion.  However the ideal
>thing is to allow anyone to use whatever they like in the file, profile what
>your output device does and use color management to handle the conversion.
>
>The only necessity is to make your output device reasonably well-behaved
>so that the output profile was also reasonable.  Most OS print systems do
>truncate to 8-bit somewhere in the flow so you don't want to loose too much.
>Linearizing to L* is one way but linearizing to gamma 1.8 would also work.
>
>Roy
>  
>
The rigidity of the 1.8 gamma and the obscure definition of middle grey 
expressed in this thread made me wonder too what we are talking about.

There has been a thread on the Colorsync list on the subject where the 
18% Kodak grey card should fall, Jon Meyer uses a method that is shaped 
in practice. It will not cover all but he selected three types of 
photography and three gammas to work with, which shows that some 
flexibility and some logic is possible in this scheme.

Quotes:

Can anyone tell me if there is a standard consensus about what Lab 
Luminosity value a Kodak 18% grey card should yield? I know there is a 
formula for calculating L* from density. I saw it once but couldn\ufffdt 
understand it. But seeing it showed me that L* could be directly 
translated into density. While testing my camera, which I suspect is 
slipping off the mark, I discovered that the best exposure of a Kodak 
Q14 greyscale target is not the same exposure that produces L*54 in a 
2.2 workspace or L*61 in a 1.8 workspace after conversion through Camera 
Raw. Now I am wondering if the Kodak 18% grey card is applicable to 
digital capture. Is there another reflective grey value that is used to 
calibrate digital cameras and if so, is it standard? Or is something 
else going on?
----------------

Bruce Lindbloom calculated that gamma 2.46 pegs 18% at L50

While this was a great index for scanner calibration, digital camera 
tone compression into 8 bit often means that the midtones get 
compromised from accurate reproduction to perceptual repro for high key, 
low key and mid key "looks". Hope this helps.

- Jon
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Thank you for your answer. By placing 18% grey at L*50 in a 2.4 space is 
it your understanding that 2.4 gamma has special importance? Since the 
same logic would place 18% grey at L*54 in a 2.2 space and 18% grey at 
L*61 in a 1.8 space.
Do you think ths means that I should continue to target L*54 if I am 
selecting Adobe RGB 1998 as an output profile space in Camera Raw 
because it has a gamma of 2.2?
-----------------

Life is full of compromises, isn't it? I personally don't endorse 
AdobeRGB because of its lack of red, yellow and green saturated detail. 
On the other hand, it is a Photoshop color settings preset which many 
people use. For sake of providing a recognizable standard, you can 
certainly do the 54s with AdobeRGB.

 From a photographer's perspective, 2.46 = 
Kodachrome/Ektachrome/Fujichrome contrast. I have a working space which 
captures the range of color and detail, while preserving the film 
contrast. Once the input profile has been converted to this space, 
preparing the image for output is the next concern.

As a drum scanner operator and a photo darkroom guy, I recognized that 
there are perhaps 3 kinds of shooters in the world:
1) Commercial/Table top
2) Fashion/MakeUp
3) Portrait

As a general rule, Photog 1) likes gamma 2.2; Photo 2) likes 2.0 and 
Photog 3) prefers a gamma of 1.8

To solve the problem I have a matched set of spaces which reduces 
contrast from 2.46 (much the same way that masking for Ciba/Ilfochrome 
or interneg used to work. This is the well known problem of how to get 
big dynamic range info into short dynamic range prints.

Please contact me off list if you think that this might be of interest.

- Jon

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> A 2.4 gamma does not play well with the usual monitor or synthetic space
> suspects of 2.2 and 1.8.

-----------------

The workflow that performs better than any other for me is to convert 
from scanner/camera profile to 2.46 using relative colorimetric, and 
then Assign the contrast specific to the photographer's intentions, 
portrait/fashion/bold saturated. This seems both scientifically and 
artistically to achieve the most accurate and most pleasing reproduction 
at the same time.

As you know, pixels get converted with the input profile conversion to 
2.46, but assigning the print contrast of 1.8/2.0/2.2, specific to the 
subject intent only affects the on-screen preview, while maintaining the 
gamut integrity and lastly "contrast masking" the image in preparation 
for the output profile/printed image.

I have been using this method since Photoshop 6 beta and have taught 
some of the most recognized photographers this paradigm. Seems to work 
well for all.

- Jon

------------------

> You don't mean to say that 2.46 correspond to some absolute scanner 
> gamma?
> Universally found in all scanner profiles?

-----------------

I can't speak for all profiling apps, however, if the scanner gradation 
is first set up for 128's in the .72 density range, (which is nearly 
equal to step 9 on most IT8 7.1 targets), and if basICColor scan+ is 
used to build the input profile with "keep gray balance" selected, then 
the native contrast and saturation of the original chrome is maintained 
into the rgb scan using this method.

- Jon

-----------------

I always set step 9 on my reflective IT8 targets to RGB 127/128 as per Bruce

Lindbloom original instructions in ColorSynergy v4.x User Guide, because I
understand that step 9 corresponds to an aim value of L* = 50. But I must
confess I never studied the mapping between RGB 127/128 to its corresponding
gamma, in the scanner profile. Why? Because it never struck me intuitively
as being important.

But now, in the context of this thread, I'll have to revisit these ideas.
Not that I particularely care about scanner gammas -- I think it's lost,
conceptually in the construction of a LUT-based scanner profile, unless one
creates matrix-shaper scanner profile -- but I'm curious as to its effect on
mapping tones onto a given RGB working space and the goal of preserving or
enhancing contrast.

Thank's for your help.  Roger Breton

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end of quotes.