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Author Topic: Using Lr Print module to prepare jpgs for printing service  (Read 1155 times)
WernerG
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« on: October 30, 2011, 03:36:09 PM »
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I want to use Lr's Print module to prepare sRGB jpgs for upload to a print service (Mpix).  Mpix only wants sRGB jpgs.  For purposes of softproofing in another program (Capture NX2), I created an sRGB jpg from the Library Module, loaded it into NX2 and applied Mpix's downloaded printer/paper profile and compare it to the sRGB jpgs.  It was clear that for this image relative colorimetric was a better choice than perceptual.  That's all I used those jpgs for. 

In Lr's Print Module, I set the "Print to:" dialog to "jpg file", set size and quality parameters and then under Color Management set "sRGB" and "relative colorimetric".  As a test I also created a second jpg using "perceptual". 

Both jpgs look identical and have identical histograms, at least as accurately as they can be displayed in Lr, yet the softproof showed clear differences.  How does Lr embed the rendering intent into the jpg in way that the printer services's printer will understand?  Does it set a flag in the EXIF?  The help file for the print module says that the "print to jpg" is for the purpose of printing at an outside service but never really explains how the rendering intent affects the jpg files that it creates.

Thank you.     
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Schewe
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« Reply #1 on: October 30, 2011, 03:51:02 PM »
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How does Lr embed the rendering intent into the jpg in way that the printer services's printer will understand?

It doesn't...when you actually print to file, the rendering intent when going from LR internal color space to sRGB will default to relative colorimetric...that's what happens when you do color space conversions of working space profiles as apposed to actual printer profiles which can do either perceptual or relcol. Not sure what NX2 is doing but working space to working space only has the single rendering intent.
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WernerG
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« Reply #2 on: October 30, 2011, 04:09:09 PM »
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Thank you Jeff,   In NX2 I compared a jpg using the printer service's profile with the sRGB jpg.  It showed differences with different rendering intents.  It has a softproof mode.  Since the Lr Print module includes rendering intent as an option in the Print to jpg mode, I was expecting that it would include that in the jpg. 

If the "print to jpg mode" doesn't use "intent" in creating the jpg, what does it do?  If nothing, why is it an active option for the Print to jpg mode?  Other printer options disappear when switching from "Print to printer" to "Print to jpg". 
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Schewe
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« Reply #3 on: October 30, 2011, 04:41:33 PM »
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If the "print to jpg mode" doesn't use "intent" in creating the jpg, what does it do?  If nothing, why is it an active option for the Print to jpg mode?  Other printer options disappear when switching from "Print to printer" to "Print to jpg". 

Are you outputting sRGB JPEGs from Print to File or are you using a printer profile?

If you are using a printer profile then yes, you should have the ability to choose rendering intents...those intents are actually used when transforming to the printer profile.

If however you are outputting sRGB JPEGs, then no, while you can choose perceptual it will only use rel col intent. That's a limitation of working space profile transforms...sRGB really only has rel col rendering intents built in version 2.x profile. Version 4 ICC profiles CAN have a perceptual intent but it takes a special download from the ICC to get a v4 working space profile.
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WernerG
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« Reply #4 on: October 30, 2011, 05:40:37 PM »
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Are you outputting sRGB JPEGs from Print to File or are you using a printer profile?

The print service instructions are very clear that uploading jpgs created with their printer profile is not correct.  The profiles are to be used for softproofing only.  They insist that only sRGB jpgs be uploaded, so yes, I'm using sRGB jpgs as the output. 

I think I'm starting to understand what you are saying.  I think that either the print service has to allow for alternative rendering intents or I have to find a way to correct the master to compensate for the changes I'm seeing in the softproof (and in prints that I've done there that show similar differences). 

Thank you again, Jeff
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