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Author Topic: Beyond calibration 2.0  (Read 2951 times)
David Sutton
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« Reply #20 on: July 22, 2013, 03:02:51 AM »
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David, thank you very much for the file. I am experiencing a problem with the color profile of the file you created. When I open it in Ps I see that it is tagged as Pro Photo. I then proceed to make a profile conversion to Adobe Rgb. The problem is that as a result the dark patches lighten up considerably. My knowledge is that if you do a "convert to profile" from Pro Photo to a 2.2 gamma color space you should not see any significant change in tonal values. But here I am seeing a difference. Am I doing something wrong or is this to be expected?
For anyone wondering why I want to convert it to Adobe RGB: I print from Lr to an Epson 3880, set to ABW mode, using a profile created with QTR software (I'm on Win7). Therefore I prefer to print a file that is already in a 2.2 gamma space, to avoid any possible problem arising from printing 1.8 gamma encoded data (I know that there should not be any issue because I am printing with a profile and not sending the data straight to the printer, but I still feel safer this way Smiley).

Cheers,
Luca
Hello Luca. I would have thought that if you stay in 16 bit you shouldn't see a luminance change going to Argb. However the change to a 2.2 gamma may be a different matter, and I don't know enough to comment.
Sorry I can't help on that one.
Cheers,
David
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picturesfromthelow
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« Reply #21 on: July 22, 2013, 05:15:49 AM »
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Hi David,
thank you for your feedback. I think I solved the issue by applying the profile, instead of converting it. The values remained the same.

Cheers,
Luca
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texshooter
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« Reply #22 on: July 22, 2013, 11:08:25 AM »
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Hi David,
thank you for your feedback. I think I solved the issue by applying the profile, instead of converting it. The values remained the same.

Why would you want to do that? When you say "applying the profile", I assume you mean "assigning the colorspace". I think when assigning a Argb colorspace to a Prophoto-tagged image the original rgb values will not change, but the appearance of those values on screen will change. So when you print the image (in this case a Prophoto gray step wedge) the ABW printer is confused by the rgb values because they are Prophoto rgb values, which are 1.8 gamma values. The ABW was not designed for 1.8 gamma source files. It gets worse. When you try to match the print results to what you see on screen, you are essentially comparing rotten apples to rotten oranges. The print is rotten because the ABW misinterpreted the Prophoto-tagged image and the monitor screen is rotten because the original prophoto  values are assigned a Argb colorspace for which is was not intended. I'm affraid you will have to create the gray target wedge from scratch inside the Argb colorspace before sending it off to the ABW printer if you want to compare apples to apples. Somebody correct me if I'm wrong.

read this:

http://ephotopros.com/articles/article-archives/articletype/articleview/articleid/156/assign-profile-vs-convert-to-profile.aspx

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picturesfromthelow
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« Reply #23 on: July 23, 2013, 03:05:09 AM »
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Hi texshooter,
when I assign Adobe RGB the values do not change, patch 1 still reads R1G1B1 and so on. If I instead convert to Adobe RGB the values change (20 becomes 35 for example). Therefore It makes sense to me to assign the profile before printing. The purpose here is to check printer performance at the extreme tone levels, so I want to be sure to send the correct tone values to the printer avoiding any possible conversion.
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texshooter
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« Reply #24 on: July 23, 2013, 04:46:44 AM »
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"when I assign Adobe RGB the values do not change, patch 1 still reads R1G1B1 and so on. "

>That may be true, but the file is still 1.8 gamma. You don't want to feed the ABW driver 1.8 gamma.

"If I instead convert to Adobe RGB the values change (20 becomes 35 for example). "

> That may be true, but at least it would be 2.2 gamma.

"Therefore It makes sense to me to assign the profile before printing. "

>Weren't you trying to avoid sending the ABW a 1.8 gamma file?

"The purpose here is to check printer performance at the extreme tone levels, so I want to be sure to send the correct tone values to the printer avoiding any possible conversion."

>I don't think printer drivers can interpret "assigned" colorspaces. the file needs to be "converted" for the new colorspace to be seen by the printer. Assigning doesn't change the file, it only changes the display.

Any help from the heavyweights?
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Ernst Dinkla
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« Reply #25 on: July 23, 2013, 05:28:24 AM »
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For what ?
As the article here points out the value changes with paper type/printer/profile.

The smart thing to do is use the chart David's provided, or one you've built yourself, and test for your own specific set up. It only takes a single sheet of paper. As the article mentions different papers can have significantly different threshold values.

Another interesting thing you can discover from the test is how much viewing light effects perceived shadow detail. You can target specific prints for their intended lighting conditions.

I think the writer of that article should have mentioned calibration/linearisation first in that article. With a printer/ink/media preset/paper that does not have that condition you could be wasting potential dynamic range and time when you adapt the methods described. Where analogue print making had a somewhat linear range (neg+pos) or at least a continuous one between the thresholds it does not have to be like that with inkjet printing.

The viewing/display light conditions was what I missed in that article too. I checked for framing behind glass and viewing light, both can cause the shadows to block even when the paper's dynamic range is wide enough. In a sense a paper linearised for the printer and its inks already meets the threshold conditions he describes, the (B&W) printer profile made of that condition should be enough. Enough viewing light should match that. It is in the display condition and display light conditions that shadows still can block. If viewing light is adapted to the expected display conditions one can correct the shadows and more with curves based on a proof print or a print of the targets discussed and add a curve like that to the print filters of Qimage for example. Image content should not be forgotten in that phase. I do not think a curve based on the targets + the adapted soft proof replaces a real proof print, it helps though.

Several 21 step wedge images have short expanded shadow + highlight ranges next to the main one. Can not recall where I got the "Technical" one from but it has the 21 step next to a continuous one and shadow + highlight ranges + 4 well chosen images. B&W all. A print made with it after linearisation/profiling tells a lot in  different viewing conditions.

There is also a bit of confusion created by the writer. 90% of photographers have a workflow that uses RGB-device printer profiles. There is an RGB>CMYK translation in all the workflows but it does not happen in the RGB-device printer profile for most. Media presets have that translation or part of it baked in. With a RIP the printer profile usually holds way more of the RGB>CMYK translation so for that condition he is right

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Met vriendelijke groet, Ernst

http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
July 2013, 500+ inkjet media white spectral plots.
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Rhossydd
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« Reply #26 on: July 23, 2013, 05:47:05 AM »
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I think the writer of that article should have mentioned calibration/linearisation first in that article.
I'm not sure that article was aimed at photographers that have printers where linearisation is an option, that's really only possible on professional wide format printers.
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Ernst Dinkla
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« Reply #27 on: July 23, 2013, 06:32:11 AM »
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I wrote "mentioned" as I did not expect that every reader of that article could go that route though we have seen that at least for B&W all kinds of DIY solutions have been found. For the users the writer could explain that today's desktop printers are already quite well linearised/profiled for the OEM papers and I wonder what this method improves on that. It will improve on that with the knowledge of viewing light - display conditions you mentioned already but that chapter was not touched. It will also correct somewhat the use of third party papers that do not fit the OEM media presets + their profile correctly.

Met vriendelijke groet, Ernst

http://www.pigment-print.com/spectralplots/spectrumviz_1.htm
July 2013, 500+ inkjet media white spectral plots.
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