Q & A : Explain the difference between Relative Colorimetric and Perceptual Rendering Intent in Printing

To submit a question to Q&A at The Photo Video Guy, just put your question into an email and send it to ross@thephotovideoguy.ca Darren writes "Does anyone have an answer for the Rendering Intent to use? I researched found Relative Colorimetric is more accurate but may produce some Banding. Perceptual will not result in banding but the color may not be as saturated or accurate. In a Henry's printing class, using  A Canon 9000 and Canon paper, I was told to have everybody use Relative Colorimetric. Everyone's prints looked like monkey poop. When I had them switch to Perceptual their prints looked much better. Most of their prints had greens and green foliage."

I think this is a great question because it confuses many photographers printing at home and because the explanations are often not very useful as I have seen.  I'll take a shot at this.

Let's agree that different mediums display colour differently.  The old CRT produced colours that look different from the IPS LED LCD displays of today.  Images that are backlit look different from those that are projected.  Prints look different based on the surface texture and finish of the paper.

I've written lots about the importance of profiling your display before you edit, and recently answered a question from Denis on printer profiling.  Darren's question comes out of that answer.

When we edit on our computers and have calibrated the display, we are working with an image that is as close to "real" as we can get.  When we go to print the image, even when the printer and paper are profiled or we are using an ICC profile, occasionally an image looks, to use Darren's words, like monkey poo.  This typically results from the rendering intent being selected.  I did a quick direct survey of folks I know who print on which of relative colorimetric and perceptual that they choose and got a resounding "Yes, if the first one looks good I stop,  If it looks bad, I try the other one."  Effective but hardly scientific.

It's All About the Gamut

What is gamut?  Gamut means the complete range or scope of something.  In an image, we typically think gamut when we think of the complete range of colours.  Printing paper has less colour gamut than a backlit LED powered LCD display.  This is why an image that screams at you on screen can have less power when printed.  Glossy papers typically have a wider gamut than matte papers, hot pressed papers typically have a wider gamut than woven papers.  I use the word typical because it means true most of the time but not always.

In this example, we see the gamut for the different colour spaces we could use in editing.  This image comes from a great document on Adobe's site called Color Managed RAW Workflow.  It was written by the inestimable Jeff Schewe.  You can download the document here.  The document was written to help people make better prints using a much older version of Photoshop so it is a bit dated.  The concepts contained therein remain absolutely viable.




We can see the horseshoe shape of visible colour and we can also see the gamut limits of the three main editing colour spaces along with an overlay of the gamut response of 2200 Matte Paper.  Plainly, working in the sRGB colour space is going to produce severe out of gamut situations and the image is going to look crappy.  If we were to use the Adobe RGB colour space, there's only a tiny bit of out of gamut area, in the yellow/orange area.  If our image doesn't have much in those colours we might be ok, but if it does, a little tuning can adjust it to fit the capability of the paper.

We work very hard editing our images using Curves, Tonal Mapping, HDR and push pull tools to maximize the dynamic range (number of stops rendered) and colour space.  Most serious editors know not to edit in sRGB or even Adobe RGB but to instead use  ProPhoto RGB.  These are all good steps but it could start to fall apart when we go to print.

Rendering Intent

Inks and papers will sometimes not have the gamut of the final image.  This translates to mean that the colour range of the image extends beyond the capabilities of the media to represent it.  While there are four rendering intents in general, only two are worked with when making photographic prints.  They are Relative Colorimetric and Perceptual.

The question you as the artist has to determine is what you want to happen when the gamut of the original exceeds the capability of the media.  There are two options provided.  In the first option, called Relative Colorimetric, we accept that there are out of gamut colours and are comfortable with losing them.  Just has excessive overexposure causes highlight clipping, we can say that in this model we have colour clipping.  The colours that are in gamut for the media are rendered accurately but colours outside the gamut are lost entirely.  This can produce images that don't look complete, or overly flat.  The colour is right, but there is stuff missing.

The alternative is Perceptual.  This is the equivalent of compression.  We take the image gamut and compress it to fit into the gamut space of the media.  We don't lose any of the colours, but we concede colour accuracy as all the colours get shifted subtly to make space for the entire image gamut in the more limited gamut of the media.   This is the generic default when your printing application doesn't ask you which one you want.  The colours are not bang on right but as much of the colour gamut as possible is preserved through the compression.  Colours towards the middle of the gamut, (see the illustrations) shift less than colours towards the edges.  If your image is composed of a lot of colours toward the gamut edges you aren't going to like it much.

perceptualrelcolIn the image at left you can see the clipping that occurs with out of gamut colours when using Relative Colorimetric.  You can also see the compression of colours that occur with Perceptual.  The graphic is from a longer article by the great people at Photozone.de.  Click here to read it.  Selecting the rendering intent is often done first.  I propose doing it last.  Let me tell you why .


Getting to the Print

In Adobe Photoshop Lightroom 5, Adobe added Soft Proofing.  It's in the Develop module and users sometimes get very confused why it isn't in the Print module since you are using it for printing.  The rationale to put it in Develop, according to Adobe folks I spoke to at Photoshop World, is that making a proof is like making a unique edit.  They're right, because I have printed the same image on vastly different papers and ended up with different edits for different papers.

Basically you do your edits and when you are ready to print, and have set up the Print module, you jump back to the Develop module and click the button to turn on proofing.  Then you MUST select the ICC profile for the printer / paper you intend to use.  If you don't do this, don't even bother going through proofing.  What Adobe has done, is to attempt to show you what the printed image is going to look like and how it will be different on different papers using the printer you selected.

What this function will do is show you where your image and rendering intent will work and where they will start to fall apart.  You can now start moving your edit sliders and curves around to pull the proof image back into a pleasing output.  It's really very powerful.  Where it frustrates people is when they have punched clarity, saturation, blacks, whites, hues and sharpness very hard to get a screen image they like only to discover it will look like turtle puke when printed.  This is a great tool as well to help decide what paper you will print on.

Let's start with a RAW image right out of the camera.  No processing done to it at all.  It's not a particularly interesting image but it does have areas of high colour saturation, one of the first places where gamut boundaries get exceeded.




Note the red berries.  Even with no editing done, we could have a gamut problem as we will see when we switch to a Soft Proof view of the same image.



Even in a low quality web image you can see that the soft proof will not look the same as the RAW image.  The colours are flatter, and I've turned on the gamut output device warning so those red berries have a marker on them to show that with the current image settings, this print will be out of gamut.


In this smaller image you can see the out of gamut warning indicators on the berries themselves.  This means that if we were to print this as is, the berry colours would be out of gamut.  They're out regardless of which intent we use, but the flattening will be greater if we choose Relative Colorimetric.  If we were to choose Perceptual the entire image colour palette will be compressed.

Softproofpanel-2Take a look next at the Soft Proof panel that appears when Soft Proofing is selected.  Here we can see the paper ICC profile being used, in this example Red River Paper's wonderful Polar Pearl Metallic using the driver for the Epson 4900.  We see that the intent being displayed is Relative Colorimetric and that we have set Lightroom to simulate the paper and ink.  That last setting is critical to be able to do the next step in making a great print that doesn't cross an out of gamut threshold.  And it is incredibly easy.


Next we see a capture of the full Lightroom screen.











I've made a Proof Copy to start.  This allows me to start with my edited version and makes a new Virtual Copy specifically to be adjusted using Soft Proofing to correct for out of gamut conditions.  In addition to the basic development settings, I draw your attention to the use of the Targeted Adjustment Tool (TAT) in both the Tone Curve and HSL panels.  By placing the TAT on the areas being flagged as out of gamut, I can make specific adjustments to correct these areas without changing the entire image.  Here even thought the out of gamut warnings are still active, they are not showing up because I have been able to leverage the point selection power of the TAT to subtly manipulate the Tone Curve and the Saturation by colour.  I always try to manipulate the image to achieve an intent of Relative Colorimetric first because it holds all the colours and keeps them accurate.  If I cannot get there entirely, that's when a flip to Perceptual will typically bring everything in line.  It's subjective at this point of course.

The really good news is that now when I print this image on the Red River Polar Pearl Metallic, it will look like it does on the display.  I find the paper and ink simulation to be very good, as close as one can come when the edit is backlit and the final print is reflective.  It's still a boring shot, but now at least it has good colours with no colour out of gamut.

I want to thank the great people who came before me and shared their knowledge such that I could teach myself and eventually share my learning with others.  And if you have questions, don't forget to send them in to ross@thephotovideoguy.ca


Q & A : Clarity on Printer and Paper Profiling

To submit your question to The Photo Video Guy Q&A just send me an email at ross@thephotovideoguy.ca Just when I think that there may go a week without a question, I am saved by good folks with excellent questions.  This one comes from Denis.

"I hope all is well and you have the time to answer a question that has come up. I watched Scott's "Grid show #113 about printing your own work. They talk about calibrating your monitor and printer with the Color Munki. If you have set up that calibration of both does that interfere with the paper profile that you down load from the paper manufactures? I have been told you need to bring your paper that you want to print on to calibrate the printer. That would mean you would have to do that to each paper you will be using.

I would like to know if that calibration over rides the paper profile. Do you have to use samples of each paper to calibrate. I have been seeing on thing and told another. I am going to allowed access to a color munki so I can calibrate both. I would like to know how this works and separate the myth form the legend  ! ! ! !"

The Scott that Denis refers to is of course, Scott Kelby, most celebrated (deservedly) of web / new media photographic instructors.  I've written and reviewed on the subject of display profiling on multiple occasions with the fundamental answer, if you edit your own work, you MUST calibrate your display.  Denis' question goes to the next level, taking that calibration to the printer.

I believe in printing your images.  There is nothing like a print in hand.  Folks wanting to make their own great prints, know that there are many choices in printers, inks, and papers to use to product final artwork.  Any paper manufacturer that is actually serious about quality printing produces ICC profiles for their papers.  Let's start there.

An ICC profile characterizes the colour space, or input device, or output device according to standards set by the ICC (International Color Consortium).  It's basically a set of rules that say to achieve this colour space, make the following adjustments to the default settings.  ICC paper profiles provide definition on how to get accurate colour representation on a particular printer, with a particular paper with a certain ink set.  That does mean what it sounds like.  For example, I use an Epson 4900 printer.  So only ICC profiles for that printer are useful to me.  If I use Red River Paper's superb Polar Metallic paper, the ICC profile is for that paper, on that printer and assumes I am using the factory ink.  Since serious printers use pigment based inks over the less accurate dye based inks, this becomes even more important because variance in pigments is reduced and archival life is substantially longer.  With rare exceptions, a print made using the manufacturer's ICC profile for the specific paper on the specific printer will do a really fine job, presuming of course that the edits were made on a computer with a calibrated display.

But there are exceptions.  Perhaps you are experimenting with different surface types.  Perhaps the paper manufacturer whose products you use doesn't have a profile for your specific printer.  Perhaps you have tried the manufacturer's ICC profile and it just doesn't look right.  This is when you need to create a custom paper profile for your workspace.  This is more work than you might think but is as accurate as you can get.

The XRite Color Munki Photo does both displays and printers.  Many calibration tools only do displays.  I have personally paid for and used a number of tools for calibration and ONLY recommend products from the Color Munki line.  Other products have produced poor results and display considerable inconsistency.

With the Color Munki photo, you print a test print directly from the software.  It creates a series of patches printed using your printer on the paper you are using.  You then use the Color Munki Photo to scan the patches.  It then does some significant math and you then print a second different test print.  You then scan its patches and the software generates a new ICC profile that is unique to your setup, your printer, your inks, your paper.  At this point, you no longer use the manufacturer's ICC profile, you replace it with your own.

In order to get a good custom profile, you must wait the required drying times specified, as ink setup takes different amounts of time depending on the paper type, and whether it has OBAs or is resin coated (RC paper).  This makes constructing a custom profile a time consuming business.  Once you've built one custom profile, you might want to build one for every paper type you use.  And that's how it works.  The ICC profile you create is only valid for the one type of paper.  You'll use ink and at minimum two 8x10 sheets and about 40 minutes for every profile you create.  In theory you should be good from then on, but professional printers recommend redoing this every time you have a major ink change, and for each new lot of paper.

I recommend keeping a binder of all patch pages and the documentation from the manufacturer on best printer setups.  I annotate the documents to what works for me.  I print exclusively from Adobe Photoshop Lightroom.  The current release offers print proof and final printer brightness and contrast controls.  When I find a setting that works for my printer and a particular paper type, I document that for next time.  I also create specific printer setups in the Print Management function on my Macintosh so the next time I am going to print on Breathing Color Crystalline Satin Canvas roll paper, a single click sets the proper platen height, dpi and other settings.  You can probably do this on Windows too.  I have no idea how and no interest in figuring that out though.

I have printed on papers from Canon, Epson, Hahnemuhle, Canson Infinity, Red River, Moab, IT Supplies, Inkpress and Kodak.  Some are great, some are truly awful, and what works best for me may not be what works best for you.

On the subject of printers, I have printed on Xerox, HP, Canon, Fuji and Epson.  For home based printing, start and stop at Epson.  HP and Xerox do great office printers.  They are not photo printer manufacturers.  Fuji is production level, not for the home or even small business.  Canon should be great and maybe the recent Pro-1 is better, but having owned the 9000 Mk I, the 9000 Mk II and the 9500 Mk II, unless you plan on printing only on Canon branded paper, bypassing ICC altogether and printing from Canon's DPP software only, do not spend one thin dime here.  It's a great system if you stay completely in family. Otherwise it's a nightmare in excessive red.  Canon reps have acknowledged this and their response is use only Canon paper.  Screw that.  I do know that one of my inspirations in printing, Mr. Martin Bailey of Tokyo, uses Canon large format IPP printers and is very happy.  I believe though that Mr. Bailey builds custom ICC profiles for everything.

To learn more about making great prints yourself I recommend a couple of resources.  First is Martin Bailey's Making the Print eBook available at Craft and Vision here.  It's wonderful and will set you back all of $5!  For more depth and detail, the "bible" on the subject is Jeff Schewe's book The Digital Print available below through Amazon (and please buy through the link to help support The Photo Video Guy).

Thanks to Denis for the question and don't hesitate to be the next question answered here on The Photo Video Guy.