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Author Topic: Beyond calibration 2.0  (Read 5301 times)

David Sutton

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Beyond calibration 2.0
« on: July 12, 2013, 09:56:00 PM »

A useful contribution I thought to the problem I sometimes get with blocked shadows. That and this post
As a result I've created some presets on my monitor to mimic the dynamic range of my favourite matte paper, and so far it works well..
It didn't take long to create a test print for density patches, and you are welcome to download it at http://davidsutton.co.nz/testprints/printingdensitypatches.jpg.
Cheers.
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athegn

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Re: Beyond calibration 2.0
« Reply #1 on: July 13, 2013, 03:13:03 AM »

Thank you for the test print.
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BarbaraArmstrong

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Re: Beyond calibration 2.0
« Reply #2 on: July 13, 2013, 04:46:08 AM »

+1 to the thank you!  I'm looking forward to trying this out on my printer, and not only determining end points to target in the files I send to print, but also comparing results among the several papers I enjoy using.  Thanks again.  --Barbara
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Rhossydd

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Re: Beyond calibration 2.0
« Reply #3 on: July 13, 2013, 07:49:08 AM »

David, unfortunately the test image you've made available isn't correct.
Load it into PS and check the actual data and you'll see lots of inaccuracies; patch #2 = 1,1,1, Patch #13 = 15,15,15 patch#234 = 238,238,238 etc.
As the test is designed to pin down exact levels, to measure errors of 4 or greater make it not as useful as it should be.

Possibly this is a result of JPG compression, but a DIY uncompressed tiff isn't too difficult to make anyway.

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digitaldog

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Re: Beyond calibration 2.0
« Reply #4 on: July 13, 2013, 11:25:19 AM »

As a result I've created some presets on my monitor to mimic the dynamic range of my favourite matte paper, and so far it works well.

Yup (as I suggested) but the best way to do this is with a 'smart display system' like the SpectraView whereby you have full control over contrast ratio and you can build a suite of calibration targets.
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Andrew Rodney
Author “Color Management for Photographers”
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texshooter

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Re: Beyond calibration 2.0
« Reply #5 on: July 13, 2013, 04:40:14 PM »

Scott Kelby says the black point should be set to R20,G20,B20.
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digitaldog

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Re: Beyond calibration 2.0
« Reply #6 on: July 13, 2013, 05:06:22 PM »

Scott Kelby says the black point should be set to R20,G20,B20.

Like most items under the subject of color management, Kelby hadn't the foggiest idea of what he's talking about.
« Last Edit: July 13, 2013, 05:15:41 PM by digitaldog »
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Andrew Rodney
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David Sutton

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Re: Beyond calibration 2.0
« Reply #7 on: July 13, 2013, 06:37:42 PM »

David, unfortunately the test image you've made available isn't correct.
Load it into PS and check the actual data and you'll see lots of inaccuracies; patch #2 = 1,1,1, Patch #13 = 15,15,15 patch#234 = 238,238,238 etc.
As the test is designed to pin down exact levels, to measure errors of 4 or greater make it not as useful as it should be.

Possibly this is a result of JPG compression, but a DIY uncompressed tiff isn't too difficult to make anyway.


Hello Rhyssydd. Yes , you are right! I didn't check the patches after making the conversion to a jpeg in Lightroom. Mea culpa. That makes the jpeg version useless.
I've uploaded a flattened version of the original tiff to the website: http://davidsutton.co.nz/testprints/printingdensitypatches.tif
The downside is it's now a 45mb file. Oh well.
Perhaps someone could double check that one for accuracy.
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Rhossydd

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Re: Beyond calibration 2.0
« Reply #8 on: July 13, 2013, 06:56:52 PM »

Yes, they measure fine now.
My own version has a black background against every dark patch and all the white patches against base white. That way it's easier to judge where the thresholds are.
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David Sutton

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Re: Beyond calibration 2.0
« Reply #9 on: July 13, 2013, 09:02:49 PM »

My own version has a black background against every dark patch and all the white patches against base white. That way it's easier to judge where the thresholds are.
What a good idea. I've followed your suggestion and updated the file.
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athegn

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Re: Beyond calibration 2.0
« Reply #10 on: July 14, 2013, 04:25:23 AM »

David

Thank you for the update.
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Rhossydd

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Re: Beyond calibration 2.0
« Reply #11 on: July 14, 2013, 04:52:05 AM »

Scott Kelby says the black point should be set to R20,G20,B20.
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.
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jedbest

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Re: Beyond calibration 2.0
« Reply #12 on: July 14, 2013, 08:50:54 AM »

Dear David,

Thank you for making this available. I look forward to testing my printer and favorite papers.

Jed
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jrsforums

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Re: Beyond calibration 2.0
« Reply #13 on: July 14, 2013, 10:09:56 AM »

For what ?
As the article here points out the value changes with paper type/printer/profile.


I may be missing something.....but, article where?
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John

Rhossydd

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Re: Beyond calibration 2.0
« Reply #14 on: July 14, 2013, 10:55:12 AM »

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jrsforums

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John

David Sutton

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Re: Beyond calibration 2.0
« Reply #16 on: July 14, 2013, 04:59:55 PM »

Hi folks.
Glad to help out.
I'm sure I should know this but any idea why the conversion to a jpeg (from prophoto rgb) should mess up the patch luminance values?
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Rhossydd

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Re: Beyond calibration 2.0
« Reply #17 on: July 15, 2013, 05:16:47 AM »

I'm sure I should know this but any idea why the conversion to a jpeg (from prophoto rgb) should mess up the patch luminance values?
JPG compresses the image data to make the data look like the original, it's not an exact replication. For the vast majority of image compression purposes rounding a value up or down by 0.4% makes no significant visible difference. The amount of data degradation can be controlled by the strength of the compression, but ultimately it's a lossy method.
In the case of charts where you need EXACT numbers JPG shouldn't be relied upon.

Having said that, I'm not sure I got it right anyway. When trying to build a chart from scratch here I found that the values set in the palettes weren't being put down correctly onto the canvas in PS CS4 anyway (at least in aRGB 8bit images). eg 8/8/8 dropped via the paint bucket measures out at 9/9/9 and just to complicate matters the pencil & brush tools deliver the correct values, and everything works as expected in 16bit mode. So it looks like there's a curious bug with the paint bucket tool in 8 bit I've stumbled on when it won't always paint the correct colours. I don't know if that's been corrected in later versions, but it's quite repeatable here.

The bottom line is that when building any test image that you want to use for determining exact values, double check what's on the page is what you expect it to be.
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picturesfromthelow

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Re: Beyond calibration 2.0
« Reply #18 on: July 17, 2013, 05:04:03 AM »

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 :)).

Cheers,
Luca
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texshooter

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Re: Beyond calibration 2.0
« Reply #19 on: July 21, 2013, 04:16:48 AM »

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 :)).

Cheers,
Luca


i might try Chart Throb to create my own 2.2 gamma step wedge.

http://www.botzilla.com/blog/archives/000544.html
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