Rendering Intent

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MEngland
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Rendering Intent

Postby MEngland » September 7th, 2016, 6:43 pm

I'm puzzled (as usual).

I've come across the terms Perceptual, Colorimetric: Relative and Absolute in discussions/articles about color management.

I'm not sure how these terms relate (if at all) to PWP's Rendering Intent options when it comes to setting the Color Management options.
Mahn England

jsachs
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Joined: January 22nd, 2009, 11:03 pm

Re: Rendering Intent

Postby jsachs » September 7th, 2016, 6:46 pm

This is from the Color Management white paper:

Maintain Full Gamut

This is also called picture intent or perceptual intent and is the default you should
normally select when working with photographic images. When you use this rendering
intent, the full gamut of color profile A is stretched or compressed to match
the full gamut of color profile B. This guarantees that all colors in both profiles will
be available, but some colors that could be matched perfectly because they lie
within both color gamuts may be altered slightly.

Preserve Saturation

This is also called graphic intent or saturation intent and is designed for working
with charts and business graphics. When converting colors, this intent preserves the
saturation of colors in profile an image at the expense of changing their hue and
brightness in some cases. This rendering intent is not intended to be used for photographic
images.

Preserve Identical Colors and White Point

This is also called proof intent or relative colorimetric intent and preserves colors
that are within both color gamuts and preserves the white point of the image. Colors
in the input image that lie outside the color gamut of the output image are changed
to the nearest matching color. This gives the most accurate possible match for colors
within both color profiles but may result in loss of color detail in areas outside
the gamut of the input or output images.

Preserve Identical Colors

This is also called match intent or absolute colorimetric intent and preserves colors
that are within both color gamuts and does not preserve the white point of the
image. Otherwise it is identical to proof intent (see above).
Jonathan Sachs
Digital Light & Color

MEngland
Posts: 11
Joined: July 13th, 2012, 7:51 am
What is the make/model of your primary camera?: Canon
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Re: Rendering Intent

Postby MEngland » September 7th, 2016, 7:35 pm

Thanks Jonathan, this clears things up. (I should have explored the white papers: I searched only this forum and the electronic manual.)

So I have just photographed a friends art works which she may wish me to print. If I was to use "Preserve Identical Colors and White Point" am I likely to get the most faithful reproduction (excluding the color of the paper on which the work was made)?
Mahn England

jsachs
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Joined: January 22nd, 2009, 11:03 pm

Re: Rendering Intent

Postby jsachs » September 7th, 2016, 8:04 pm

Actually, I use Maintain Full Gamut almost all the time. The problem with the other modes is that out of gamut colors get clipped instead of being compressed to fit the printer gamut. This happens more often than you might think since a lot of bright saturated colors on the screen cannot be reproduced by most printers. The colorimetric modes are more important when you need an absolute color match, for example when printing images for a clothing catalog or for reproducing paint colors. If you want to reproduce artwork really well, resign yourself to printing a lot of proofs and tweaking the brightness and color until you get the best result. The last time I did this for someone I found the selective color correction transformation particularly helpful.
Jonathan Sachs
Digital Light & Color

MEngland
Posts: 11
Joined: July 13th, 2012, 7:51 am
What is the make/model of your primary camera?: Canon
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Re: Rendering Intent

Postby MEngland » September 7th, 2016, 8:09 pm

Thanks again! Great advice to match an excellent product.
Mahn England

Charles2
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Re: Rendering Intent

Postby Charles2 » September 7th, 2016, 8:49 pm

Just for completeness, I note that we have one more choice: Color | Profile | Rendering Intent, and the dropdown menu also has Preserve Identical Colors + Black Point Compensation.

jsachs
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Joined: January 22nd, 2009, 11:03 pm

Re: Rendering Intent

Postby jsachs » September 7th, 2016, 10:30 pm

That one is for Photoshop compatibility as they have a Black Point Compensation option. Frankly I've long since forgotten what it does but you can google it.
Jonathan Sachs
Digital Light & Color

Charles2
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Re: Rendering Intent

Postby Charles2 » September 8th, 2016, 12:06 am

Ok,I did a search and instant study, making me a Web-certified expert. Apparently, BPC aims to lighten the darkest shadows in a smooth way that keeps more detail in them. So if you want Relative rendering intent, it seems one should have BPC on most of the time. BPC is not relevant to Perceptual rendering intent.
http://www.gamutvision.com/docs/blackpoint.html
http://www.colourphil.co.uk/rendering_intents.shtml

jsachs
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Re: Rendering Intent

Postby jsachs » September 8th, 2016, 3:02 pm

The idea behind black point compensation is apparently to attempt to compensate for the fact that black as reproduced by a printer is not nearly as dark as you get from a monitor. Just how dark the blackest blacks are depends on the printer, inks, viewing conditions and paper. This problem is especially bad in 4-color printing. Black point compensation is performed by tweaking part of the tone curve that controls shadow reproduction when converting image data to the printer color space.
Jonathan Sachs
Digital Light & Color


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