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Author Topic: Rendering Intent and Blackpoint Compensation  (Read 16909 times)

dennysb

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Rendering Intent and Blackpoint Compensation
« on: December 13, 2007, 12:30:38 pm »

I was reading the very educational web page from Eric Chan, regarding the Epson 3800 (http://people.csail.mit.edu/ericchan/dp/Epson3800/printworkflow.html).

In this page, he stated the following instrcution regarding the enabling or disabling the  Black Point Compensation. I was under the impression that  Black Point Compensation should be left ON.

I would appreciate some feedback on this....

PS: From my viewing of the "From Camera to Print" Video Journal, I understood it should be ON at all times.


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"Set the Rendering Intent menu and Black Point Compensation checkbox appropriately, based on your soft-proofing results in Step 1 (see above). Either you should:

set the Rendering Intent menu to Perceptual and uncheck Black Point Compensation, or
set the Rendering Intent menu to Relative Colorimetric and check Black Point Compensation."
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PhillyPhotographer

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Rendering Intent and Blackpoint Compensation
« Reply #1 on: December 13, 2007, 12:34:26 pm »

Quote
I was reading the very educational web page from Eric Chan, regarding the Epson 3800 (http://people.csail.mit.edu/ericchan/dp/Epson3800/printworkflow.html).

In this page, he stated the following instrcution regarding the enabling or disabling the  Black Point Compensation. I was under the impression that  Black Point Compensation should be left ON.

I would appreciate some feedback on this....

PS: From my viewing of the "From Camera to Print" Video Journal, I understood it should be ON at all times.
----------------
"Set the Rendering Intent menu and Black Point Compensation checkbox appropriately, based on your soft-proofing results in Step 1 (see above). Either you should:

set the Rendering Intent menu to Perceptual and uncheck Black Point Compensation, or
set the Rendering Intent menu to Relative Colorimetric and check Black Point Compensation."
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[a href=\"index.php?act=findpost&pid=160390\"][{POST_SNAPBACK}][/a]

Perceptual = off

Relative Colorimetric = on

digitaldog

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Rendering Intent and Blackpoint Compensation
« Reply #2 on: December 13, 2007, 01:04:13 pm »

BPC should be on for color space conversions. But for soft proofing, the way it works is as follows:

•Simulate Paper Color and Simulate Black InkOff: Convert using the
relative colorimetric intent with Black Point Compensation.
•Simulate Black Ink: Convert using the relative colorimetric intent
without Black Point Compensation.
•Simulate Paper Color: Convert using the absolute colorimetric
intent (no Black Point Compensation).

With the absolute colorimetric intent, Black Point Compensation is always off.
« Last Edit: December 13, 2007, 01:05:09 pm by digitaldog »
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Sunesha

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Rendering Intent and Blackpoint Compensation
« Reply #3 on: December 13, 2007, 01:52:44 pm »

Thanks that was real useful info.

Anyone know what preserve RGB numbers is for?

It always look like crap when checked. So I always wondered when it is used or what is for.

Cheers,
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Daniel Sunebring, Malmoe, Sweden
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adion

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« Reply #4 on: December 13, 2007, 02:05:24 pm »

OK, so when exactly should i check it?
I'm a bit confused...  
But It's always based on the way i softproof it right?

If I softproof it in perceptual with it off, then i print it in perceptual wit it off, right. Or is there another way?

I always softproof my images in relative colormetric with BPC turned on and then print it with the same settings with my printer/paper profile matching but the relative colormetric way is not always the best result for each image.
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digitaldog

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« Reply #5 on: December 13, 2007, 02:08:04 pm »

Quote
Thanks that was real useful info.

Anyone know what preserve RGB numbers is for?

[a href=\"index.php?act=findpost&pid=160411\"][{POST_SNAPBACK}][/a]

Show me what the current numbers would look like IF I sent them to this device WITHOUT converting to the output color space.
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Sunesha

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Rendering Intent and Blackpoint Compensation
« Reply #6 on: December 13, 2007, 03:47:16 pm »

Quote
Show me what the current numbers would look like IF I sent them to this device WITHOUT converting to the output color space.
[a href=\"index.php?act=findpost&pid=160418\"][{POST_SNAPBACK}][/a]
Yikes, but it could be useful for trouble shooting. Then I am glad I always proofed even not fully understanding to make a print perfect.

Cheers,
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Daniel Sunebring, Malmoe, Sweden
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digitaldog

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« Reply #7 on: December 13, 2007, 03:53:17 pm »

Quote
Yikes, but it could be useful for trouble shooting. Then I am glad I always proofed even not fully understanding to make a print perfect.

Cheers,
[a href=\"index.php?act=findpost&pid=160446\"][{POST_SNAPBACK}][/a]

Its more useful for CMYK workflows. Someone sends you a CMYK with the U.S. Web Coated (SWOP) v2 profile but you're using a different output device of which you have a profile. There's no RGB document so your choice is, send the CMYK values to your device (or muck around trying to convert it back to RGB). So you use the Preserve Color Numbers and see that the U.S. Web Coated (SWOP) v2 image doesn't look awful (or it does). Now you can decide if you want to send the numbers "as is" to the device or take other actions.
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Sunesha

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Rendering Intent and Blackpoint Compensation
« Reply #8 on: December 13, 2007, 04:30:16 pm »

Quote
Its more useful for CMYK workflows. Someone sends you a CMYK with the U.S. Web Coated (SWOP) v2 profile but you're using a different output device of which you have a profile. There's no RGB document so your choice is, send the CMYK values to your device (or muck around trying to convert it back to RGB). So you use the Preserve Color Numbers and see that the U.S. Web Coated (SWOP) v2 image doesn't look awful (or it does). Now you can decide if you want to send the numbers "as is" to the device or take other actions.
[a href=\"index.php?act=findpost&pid=160449\"][{POST_SNAPBACK}][/a]
I understand now, thank you for answering so extensive and with good explaining.

I am just starting to learn color-managing. Which is a lot harder than I thought from the beginning.

I learned monkey way, try and see what happens. I know a lot "how" now, but I miss a lot off "why" in my internal knowledge database   .

Cheers,
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dennysb

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« Reply #9 on: December 13, 2007, 05:50:27 pm »

Thanks everyone I think I got it,

I did not realize I need it to have BPC off when using Perceptual. That is a good thing to know since I make my decision on the Rendering Intent after looking at the soft proofing results on the screen, and many times I go the Perceptual way

I would also assume this rules ought to be followed at the printing phase, that is selecting the same Rendering Intent as well as the correct BPC mode.

Thanks again...Dam! this place is so good for collecting information  
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Dennys Bisogno
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digitaldog

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« Reply #10 on: December 13, 2007, 06:07:33 pm »

Quote
I did not realize I need it to have BPC off when using Perceptual.
[a href=\"index.php?act=findpost&pid=160485\"][{POST_SNAPBACK}][/a]

You don't and you shouldn't. I have no idea why anyone would suggest this, at least when making conversions for output (NOT soft proofing).

BPC either does nothing or it does something very useful: Mapping source to destination black.
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dennysb

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Rendering Intent and Blackpoint Compensation
« Reply #11 on: December 13, 2007, 08:21:40 pm »

Oh yes, I always leave on when I am in the print window. My question related to whether I should leave on when soft proofing. So i think I am in the right track now. Or maybe not    

Quote
You don't and you shouldn't. I have no idea why anyone would suggest this, at least when making conversions for output (NOT soft proofing).

BPC either does nothing or it does something very useful: Mapping source to destination black.
[a href=\"index.php?act=findpost&pid=160489\"][{POST_SNAPBACK}][/a]
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digitaldog

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« Reply #12 on: December 14, 2007, 09:19:18 am »

Quote
Andrew,

JUST FOR SOFT PROOFING using PERCEPTUAL rendering intent does it matter if BPC is on or off?

Thanks
[a href=\"index.php?act=findpost&pid=160593\"][{POST_SNAPBACK}][/a]

For soft proofing, you're not using Perceptual to the display:

•Simulate Paper Color and Simulate Black InkOff: Convert using the
relative colorimetric intent with Black Point Compensation.
•Simulate Black Ink: Convert using the relative colorimetric intent
without Black Point Compensation.
•Simulate Paper Color: Convert using the absolute colorimetric
intent (no Black Point Compensation).

Those options are controlling the mapping of the display transforms, not the output itself (the simulate check boxes). That's why they say "Display Options (on screen only).

For conversions, you want BPC on all the time as discussed.
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walter.sk

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« Reply #13 on: April 30, 2008, 04:45:25 pm »

Quote
For soft proofing, you're not using Perceptual to the display:

•Simulate Paper Color and Simulate Black InkOff: Convert using the
relative colorimetric intent with Black Point Compensation.
•Simulate Black Ink: Convert using the relative colorimetric intent
without Black Point Compensation.
•Simulate Paper Color: Convert using the absolute colorimetric
intent (no Black Point Compensation).

Those options are controlling the mapping of the display transforms, not the output itself (the simulate check boxes). That's why they say "Display Options (on screen only).

For conversions, you want BPC on all the time as discussed.
[a href=\"index.php?act=findpost&pid=160645\"][{POST_SNAPBACK}][/a]
Rodney:  I thought I understood this but in the months since this thread I find that my footing is precarious!

In printing to the Z3100, I follow HP's recommendation to send the output to the printer using Perceptual Intent, and I keep BPC on.

If I want to softproof using Simulate Paper Color, it seems you say that I cannot use Perceptual Intent in the softproof dialog box, but must use Absolute Colorimetric with BPC off.  I would then duplicate the image, and adjust the one being softproofed so that it comes closest to what the unsoftproofed copy looks like.

How, then, would I go about softproofing to see whether Perceptual or Relative Colorimetric would be the best choice for my output file?

I also have been  told that using Simulate Paper Color is the best choice for seeing the way the print will look.

I feel as if I'm walking in quicksand with this stuff.  I had been setting the softproofing dialog using my printer profile, Perceptual Intent, BPC off, and Simulate Paper Color on.  So far, the file I send to the printer, which has an adjustment layer or two to make it match the original file, has been producing prints with no real surprises.

I guess what I am asking is this: What settings in the softproofing dialog box would best let me compare how Relative Colorimetric and Perceptual Intent rendering would look, as displayed on my monitor?
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digitaldog

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« Reply #14 on: April 30, 2008, 07:44:59 pm »

Quote
If I want to softproof using Simulate Paper Color, it seems you say that I cannot use Perceptual Intent in the softproof dialog box, but must use Absolute Colorimetric with BPC off.
[a href=\"index.php?act=findpost&pid=192730\"][{POST_SNAPBACK}][/a]


That's the rendering intent for the soft proof! You can select Perceptual of course. But when you do so, and you pick the simulate check box, the intents above are what is used to produce the soft proof to the screen.
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walter.sk

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« Reply #15 on: April 30, 2008, 09:49:16 pm »

Quote
That's the rendering intent for the soft proof! You can select Perceptual of course. But when you do so, and you pick the simulate check box, the intents above are what is used to produce the soft proof to the screen.
[a href=\"index.php?act=findpost&pid=192762\"][{POST_SNAPBACK}][/a]
So if I want to see what my printer profile will do if the file is sent to the printer with Perceptual Intent, BPC on, I would set up the soft proof dialog with my paper profile, Absolute Colorimetric Intent, BPC off and Simulate Paper Color checked.

If I want to see what my printer will do if the file is sent with Relative Colorimetric Intent, BPC on, I would set up the soft proof box with my paper profile, Relative Colorimetric Intent, BPC off, and Simulate Black Ink on.  I would not really be able to see what Relative Colorimetric Intent would look like, then, if Simulate Paper Color were checked?

So, if I wanted to A-B the comparison between printing with Perceptual and Relative Colorimetric intents should I have two copies of the file on screen, each with one of the softproof setups, or is there an easier way to do it?

And if there is no way to soft proof Relative Colorimetric with Paper Color checked, then the above comparison would be meaningless, or so it seems to me.

I know my left-brain functioning leaves something to be desired at this point, but I'm beginning to have doubts about the other hemisphere as well
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Zachary

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« Reply #16 on: April 30, 2008, 10:06:59 pm »

I think a couple of screen shots might clear things up.
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digitaldog

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« Reply #17 on: May 01, 2008, 08:48:45 am »

Quote
So if I want to see what my printer profile will do if the file is sent to the printer with Perceptual Intent, BPC on, I would set up the soft proof dialog with my paper profile, Absolute Colorimetric Intent, BPC off and Simulate Paper Color checked.

You're confusing TWO processes here using profiles and rendering intents.

1. The rendering intent for conversion to the output color space (the numbers you send to the printer).

2. The rendering intent used to provide the soft proof.

You can setup Perceptual for output to the printer and turn on the Simulate check boxes to provide the soft proof which itself is using Absolute Colorimetric intent to the display.
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neil snape

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« Reply #18 on: May 01, 2008, 10:01:29 am »

There is still confusion around BPC in Perceptual.
It is a legacy trigger or switch for some very old profiles that didn't have the tables in the right tags, they were basically copied tables from relative where BPC was not available in programs at the time, normally proofing rips etc.
Any modern recent profile will have the BPC already calculated in the perc tables so the BPC switch is not going to make any difference checked or not for these profiles. Perhaps there is a minor hit , very minor in the ACE for verifying the BPC being in the tables, that I don't know.

In any case BPC on or off in perceptual isn't going to make any difference in recent profiles in any way printing or proofing.

IF you are hard proofing follow Andrew's workflow which is correct.
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