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Author Topic: What is Rendering Intent?  (Read 3420 times)
Craig_P
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« on: February 16, 2007, 09:08:29 PM »
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Can someone tell me what Rendering Intent is?  How much impact will the setting have on prints?
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francofit
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« Reply #1 on: February 17, 2007, 03:27:38 AM »
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Can someone tell me what Rendering Intent is? How much impact will the setting have on prints?
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If you haven't yet read anything about Color Management I would suggest to start looking on the net for free information (there is plenty of it, like e.g. [a href=\"http://www.cambridgeincolour.com/tutorials/color-space-conversion.htm]here[/url] -index is here-) then get a book on Color Management like that one of Bruce Fraser or Andrew Rodney aka digitaldog.

A short practical answer about Printer Rendering Intent  for photography I have seen most of photographers agrees on is that the Relative Rendering is generally the best while for some specific kind if images the Perceptual one may give some better results (so, after having understood the theory, experiment and experience play an important role).
« Last Edit: February 17, 2007, 04:21:53 AM by francofit » Logged

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bjanes
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« Reply #2 on: February 17, 2007, 07:33:29 AM »
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Can someone tell me what Rendering Intent is?  How much impact will the setting have on prints?
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[a href=\"http://www.creativepro.com/story/feature/12641.html]Bruce Fraser[/url] has a good article on rendering intents, which basically determine how the color management system handles out of gamut colors.

Bill
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nemophoto
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« Reply #3 on: February 19, 2007, 08:53:07 AM »
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Can someone tell me what Rendering Intent is?  How much impact will the setting have on prints?
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In a nutshell, "Rendering Intent" is the translation of color pixels from one kind of device (I.E. - digital camera, RGB, monitor) to another -- inkjet, laser, offset printing. It describes how the translation occurs and how much "fudge factor" or "pleasing color" is used. (Not a scientific or technical way of describing what happens.) This is a massive, but over simplified description. You'll get other, more technical, answers from other people.

Once upon a time, I used "Perceptual" when printing my images, but no more. I always use "Relative Colormetric". This is regardless of whether I'm printing an RGB or CMYK image to my laser or inkjet or RIP/inkjet for proofing. I've felt I had more accurate, though mostly "unseeable" translation.

Hope this helps a little.

Nemo
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kiiquu
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« Reply #4 on: February 20, 2007, 06:50:56 AM »
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Can someone tell me what Rendering Intent is?  How much impact will the setting have on prints?
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Rendering intent has to do with how colours are translated when moving between two colour spaces which aren't identical. When you choose a Rendering Intent you are telling photoshop how to translate colours which are in your file's colour space (working space) but not in your printer's colour space.

Relative Colorimetric simply says that any colour that is in your working space and in your destination space (print space) should just stay the same whereas colours in your working space but not in your print space should simply be reinterpreted to the closest colour which does exist in your print space. This  will produce more accurate colours for hues which are in both the source space and print space but may produce flat or dull colours for working space colours if they are out of gamut in your printer space as they will be crunched down by this intent to fit them into the print space.

Perceptual Intent also deals with how to handle the mismatch between colours in the working space and the print space. But it uses a different tactic. Perceptual intent will try to preserve the relationship between all colours including the saturated ones in your work space which will be out of gamut in the printer space by squeezing and altering slightly the entire  gamut of colour so as to maintain the overall balance and maintain the original's effect.

If you have enough saturated colour in a working space which is outside your print space then Perceptual Intent will do a better job of maintaining the "punch" of an image but at the cost of overall colour accuracy.  

If most of the colours in your working space are also in the print space then choose Relative Colorimetric as it will maintain more accurate colour.

There is no right answer on which to use in general. You need to judge on an image by image basis. Typically images with highly saturated colours will benefit from Perceptual Intent. Images without highly saturated colours will typically be more colour accurate with Relative Colorometric. So the size of your print space (ie which printer you use) will play a role in which you choose. Better printer=bigger print gamut=less need for perceptual

Use custom softproofs and out of gamut warnings in Photoshop to help you make this decision if you're not sure.
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bjanes
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« Reply #5 on: February 20, 2007, 08:36:12 AM »
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Relative Colorimetric simply says that any colour that is in your working space and in your destination space (print space) should just stay the same whereas colours in your working space but not in your print space should simply be reinterpreted to the closest colour which does exist in your print space.
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I think that this is a good explanation, but I disagree with the following:

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This  [Relative Colorimetric] will produce more accurate colours for hues which are in both the source space and print space but may produce flat or dull colours for working space colours if they are out of gamut in your printer space as they will be crunched down by this intent to fit them into the print space.
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Relative Colorimetric does not compress colors but merely clips them to the most saturated tone that the printer can produce. This produces saturated colors, but may result in posterization and banding. Perceptual is the rendering intent which compresses colors to fit in the destination space and can cause desaturation.


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Perceptual Intent also deals with how to handle the mismatch between colours in the working space and the print space. But it uses a different tactic. Perceptual intent will try to preserve the relationship between all colours including the saturated ones in your work space which will be out of gamut in the printer space by squeezing and altering slightly the entire  gamut of colour so as to maintain the overall balance and maintain the original's effect.
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That is true, but unfortunately current perceptual rendering engines are not "smart", that is they compress the gamut by a predetermined amount without actually checking to see if those colors are actually in the image. This is most likely to occur when the image has many saturated colors and is in a wide space such as ProPhotoRGB. Since the source space is converted into the PCS (profile connection space, often CIE L*a*b*), the color engine does not know the source and compression is the same for sRGB and ProPhotoRGB. [a href=\"http://www.steves-digicams.com/techcorner/July_2005.html]Here[/url] is a simple explanation of the above matters.


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If you have enough saturated colour in a working space which is outside your print space then Perceptual Intent will do a better job of maintaining the "punch" of an image but at the cost of overall colour accuracy. 

If most of the colours in your working space are also in the print space then choose Relative Colorimetric as it will maintain more accurate colour.
[a href=\"index.php?act=findpost&pid=101878\"][{POST_SNAPBACK}][/a]

IMHO, you should normally use Relative Colorimetric if you do not have a lot of out of gamut colors and clipping is not bothersome. The print will have more saturation. However, if you have a lot of out of gamut colors, Perceptual may be a better choice, depending on soft proofing and sound judgement. However, rather than maintaining "punch", colors are desaturated. More advanced users may use relative colorimetric and edit the image selectively so that out of gamut colors are smoothly brought into range.

Bill
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Ray
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« Reply #6 on: February 20, 2007, 07:05:49 PM »
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Can someone tell me what Rendering Intent is?  How much impact will the setting have on prints?
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I take it we are making an assumption here that you are using 'Proof Setup' in relation to a specific paper profile and have 'simulate paper color' ticked and 'gamut warning' ticked. I assume also that you are using a calibrated monitor and expect to get a print that closely approximates what you see on your monitor.

If this is the case, then you can see the effect that the various rendering intents have on any particular image you are viewing, by toggling amongst the various intents in proof setup.

My impression is that Rel Col significantly dulls the image but tends not to show areas that are out-of-gamut. However, before printing with Rel Col the image always needs (in my experence) drastic increases in saturation and local contrast, which could result in patches of out-of-gamut colors then appearing on the monitor.

Absolute Col tends to leave the image looking pretty much the same as you see on the monitor but tends to show out-of-gamut colors in the shadows.

I often use Absolute Col when I'm already satisfied with the appearance of an image I don't want to significantly rework it in Rel Col.

If I want to make a big splash with fully saturated colors, I'll use Saturation Intent.

I always do my best to remove the grey splotches, indicative of out-of-gamut colors, before printing.
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