Digital BW, The Print

I don't have time to post here much if at all lately but your post caught my eye.  There was a very old thread called tonal range and linearization - or something like that.

Plot a line from (0,0) to (100,100) and call it L* (LAB colour space, denoting luminance).  If you prefer, cut the x axis into 8 bits 0-255 or 16 bits if fanatical.

Now on the same chart, plot a straight line from, say, (0,14) to (100,97).  Dmax = L* of 14 and paper white = L* of 97, something like matt paper.  Change the numbers if you like but hopefully you get the point. If you have linearised your printer L* output luminance production will be a straight line from ink black to paper white.  (That is afterall what linearisation is.)

Now look at this line in comparison to a perfect L* plot (with it's perceptually close gamma, not far from 2.2 blah blah blah).  How much is lighter than perfect?  How much is darker? If you want, plot a third line with a better black and brighter white - label that one your very good Eizo display.

The challenge of colour management (all parts of the chain: file to printer, file to display etc) is how to transform a file from perhaps an imperfect capture colourspace, through a perfect working space and on to an imperfect output device/space. The ball starts rolling with black point compensation and white point compensation.

We tend to ignore using WPC when previewing prints on a display because our eyes are very good at adjusting white point.  But if you want a sense - on the display - of the lack of black you do need to use BPC.  Yet, most of us likely hate the shock we get and just leave it for the print itself.

If your B&W image is sent to print as a colour file with 'normal' colour management ICC profile (we all hate this because of the bad use of colour ink in the greyscale but let's bear with it for a second) an intrical part of the mapping from file space to print space is the adjustment for the black point and white point of the ink/media as recorded in its ICC profile. You can read various Adobe tutorials as to how the file numbers are adjusted for this BPC/WPC. With B&W printing and particularly to matte paper it's the BPC that affects us most because, while getting better, dMax is still wanting.

So the challenge is/was how to map into a compressed/constrained gamut and a straight line linearised L* doesn't do the job very well. What BPC does is resurrect a better gamma around the mid tones. Of course that means something needs to give and, yes, as with colour printing, BPC means some compression most notably in the shadows because that's the part that's far from perfect.

Even though Epson ABW printers are well linearised when they leave the factory, plot a step wedge with ABW and plot L*.  You'll notice it isn't a straight line.  They've embedded some BPC/WPC.  It changes with paper selection. They get it.

What QTR Create ICC did, in short, was to take this 'greyscale colour management' and apply it to greyscale printing i.e. take the luminance management and ignore the a* and b*. Think of it colour management of L*. It does the same gamut mapping we use all day long but, of course, only with respect to luminance.  BUT one of the tangential cool things about the files was that it could also capture the a* and b* information of your printed step wedge.  This allows proper tonal proofing and the ability to impound that tone on a digital copy of the file for electronic distribution / posting on the web etc. (You can post those cool warm tone images of majectic lions or cheetahs overlooking a windswept plan and with incredibly ominous and heavily manipulated clouds looming overhead.  They just don't look as cool if they're perfectly neutral and they wouldn't match the toning of the book you intend to sell millions of copies of.)  You can print a step wedge with your favourite ABW settings (or whatever RIP you prefer), measure it and not only use the QTR ICC profile to do the luminance mapping with a CMM but preview the tone while you edit the image.

Genius.

Of course then Apple and Adobe decided to throw in some speed bumps in the way they managed colour management but these were easily overcome. (Perhaps they have thrown up more but I haven't printed for quite some time now.)

HTH

Steve

On 29 Jan, 2015,at 08:30 PM, "richard@richardboutwell.com [DigitalBlackandWhiteThePrint]" <DigitalBlackandWhiteThePrint@yahoogroups.com> wrote:
> Steve, I tried going back to look at the original posts about the push to get QTR-Create-ICC built, but I could only find entries after it was already released. But could you elaborate on what you mean by "draw a straight line from an imperfect black and imperfect white"? By imperfect do you mean paper white not being 100% reflective and whatever the inks' D-max not being 0% reflective?
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> If you look at the pictures in my post, the first one is a down sampled file used to make the resulting prints (gray gamma 2.2 converted to sRGB) and is essentially identical to the QTR print with no color management. What I find when using ABW, or QTR and an ICC profile, is that the prints always have compressed shadows. In theory and computer maths that might be what is supposed to happen, but for me, it doesn't make a better print.
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> Which is to say, I understand the reason for using the QTR ICC profile workflow, but I choose not to for printing black and white (printing color is a different story). This decision is based on how I build my profiles and observing the effect printing with ICC profiles has on the actual print (which sounds like a case of "it works for me"). The approach I take comes from growing up printing on Azo and then platinum/palladium and being accustomed to the long straight line with rich blacks and smooth open shadows—there might not be "detail" in the shadows the print has a rounder and smoother three-dimensional feeling. When I translate that to inkjet printing: Using QTR with an ICC profile (and rendering intent with black point compensation) or the Epson ABW driver setting that causes the tones to stop increasing smoothly from 95% through 100%K and the resulting print has feeling of flatness even though "more black" is supposed to give the appearance of more contrast. I want to go back and reread Keith Coopers' review of the new Epson printer from last week. I think he addresses some of this there. 
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> Ok, I'm getting back to work. Those scans aren't going to retouch themselves. . . 
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> Richard Boutwell
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