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Motivation is a photography blog that discusses the creative aspects of photography. The posts will include thoughts about images and their interpretation, photographers and their work, technique, workflow, my ongoing projects, and perhaps even the occasional off topic rant.

Basic Color Management For Photographers - Part IV

Part IV - Putting It Together

Here we are in the fourth and final installment in this series about basic color management for photographers. In Parts I-III we covered why profiles are useful, how they are generated, and what part they play in a color managed workflow. In today’s post I would like to discuss how these profiles and color spaces are actually used in Photoshop and how they are used to make a print.

This can be a bit difficult to demonstrate very specifically because there are several brands of inkjet printers and within those brands there are multiple models, all of which may have different appearing printer drivers. However, all the drivers will have all the settings I talk about located somewhere within their dialogues. Likewise, there are several different types of photo editing software and even within those brands there may be different versions (ie Photoshop and Photoshop Elements) that are slightly different. Again, they all tend to have the same types of settings, albeit sometimes located in different locations within their menus. While I personally use both Adobe Lightroom and Adobe Photoshop CC for editing, I do my printing from Photoshop CC. In terms of printers, I used to use Epson printers but switched over to Canon a few years ago.


First up, let’s look at some of the the color management settings (I have added highlighting to the ones that I will be talking about) in Photoshop under Edit>Color Settings:

Photoshop Color Management Dialogue

Photoshop Color Management Dialogue

It looks a little confusing, but it really isn’t (now that we know all about color spaces). When you import an image from Lightroom to Photoshop, or when you open a photo on your hard drive, it opens (hopefully) within a specific color space to which it was assigned. That color space is typically either Adobe RGB, ProPhoto RGB, or sRGB, and the photo carries a color space ‘tag’ of sorts so that Photoshop ‘knows’ what color space the photo is in when it is opened. It then knows how to display the photo and how to make your edits effect the color. Of course, if you are working in a color space larger than your monitor can display then your monitor compresses it visually, but Photoshop still keeps it in the embedded color space so the actual color information is retained even if it can’t be properly displayed. The compression is only a ‘monitor thing’ and doesn’t result in lost color data. Then, when you print on a machine that can print more colors than your monitor can display, the colors that the monitor had to compress are visible and unchanged.

Lets start at the beginning. The ‘Working Space’ section of the dialogue box simply asks what color space you want to be working or editing in when you are using any specific color model. For example, in the above screen grab, when I use the RGB color model Photoshop expects me to be working on images in the ProPhotoRGB color space (when intending to print our work, the color space to work in would typically be either AdobeRGB or ProPhotoRGB , while sRGB is more appropriate when images are intended to be displayed on-line). I typically work in ProPhoto because in the future it is quite possible that devices may print in ever larger color gamuts and I want to retain all the color information I can. There are valid reasons one might choose Adobe RGB as well.

But, what happens when a photo is opened that is tagged with a color space other than what you have chosen in the dialogue box? For example, lets say I open an image that I had previously prepared for the web and it’s in the sRGB color space. Photoshop knows that this isn’t what you expected for an RGB color model image (because it isn’t chosen as the RGB working space). That’s what the section called ‘Color Management Policies’ is for.

Under ‘Color Management Policies’ one typically would want to preserve the profile that is embedded in the image (or some might say the color space the image is tagged with). But what if the color space of the image you are opening is not the one you have chosen as your RGB color space? The setting in “Profile Mismatches” tells the software what to do. My choice in this instance is to notify me and ask me what to do if that to were happen, rather than doing something behind the scenes without telling me. The choices it will give me if that happens are to either open the image in the embedded color space or to convert it over to the working color space.

That’s all fine and good, but what happens if we are converting an image from a larger color space into a smaller one, such as would occur if we were opening a ProPhotoRGB tagged image and we had our RGB Working Space set to Adobe RGB? One could ask the same question about printing. What happens if we are printing from ProPhotoRGB on an inkjet printer, as the printer can not print all the colors that are in that color space. In both these instances our software needs to decide what to do with the colors that ‘don’t fit’ or are unprintable. There are two possible choices, called rendering intents. These are the so called relative colorimetric and perceptual intents and you can choose either. In general, for color space conversions I use Relative Colorimetric and for printing I try them both and see which looks better..

When using Relative Colorimetric for making profile conversions the software will simply move the colors that lie outside the color space to the closest color that is in the new color space. For printing it will move the color to the closest color the printer can reproduce based on the icc profile for the paper you are printing to. As an example, lets say there is a very bright red in the image that the printer can’t reproduce on a specific paper (it ‘knows’ this based on the printer/paper profile you have chosen - more on this later). It will take that red and print it as a red of the exact same hue, but it will make it as ‘bright’ as the paper will allow. Essentially it just moves the red down the color space axis until it is within the gamut of colors that the printer can reproduce. The only downside is that our red that was out of gamut now looks no different than the brightest other red of that hue in the print, and the viewer can’t tell that the two reds were in any way different.

The Perceptual rendering intent takes another tact. It says that instead of moving that out of gamut, non-reproducible bright red down the axis and leaving it at that, it moves the red down the axis to the brightest level that can be printed on that paper, but then it also moves all the reds of that hue down the axis a bit, so that the original red is still a bit brighter than the other reds. At least that’s a good way to visualize what happens.

Finally, what happens if you try to open an image in Photoshop that has no color space associated with it (gasp)? You know, the one that your Uncle Joe emailed you ;) Well, if you look all the way down on the lower left under the Color Management Policies, I have asked Photoshop to tell me if that happens and let me choose what to do. If that were to happen it will present a dialogue to me and ask me if I would like to leave it untagged or move it into a color space and, if so, it will allow me to choose which one.

OK, we made it through the Photoshop tough stuff. We could also go into Photoshop soft-proofing, but that is a bit beyond the basics.

Now let’s take a look at how those printer/paper profiles we made in Part III are used. After all, at the end of the line we do want to make a print.

Driver Interface For Canon ImageProGraf 2000

Driver Interface For Canon ImageProGraf 2000

One (among many) of the reasons we had to go through the Photoshop color management settings is so we could understand what we are seeing in the printer driver. I will be demonstrating with the driver from my Canon ImagePrograf 2000, but all drivers - Epson, HP, etc - will have the same choices in their particular drivers. The trick is to find out what they call the choices and where it is buried in the driver menu. I no longer have my Epson printer so can’t easily demonstrate that driver - but it’s all in there.

What you see above is the dialogue in Photoshop that opens up when an image open and you go to File>Print. You can see at the top that the printer I am using is the Canon Pro 2000. If you have other printers they can be chosen from the drop down as well. Lets go down to the color management section. What I have labeled as #1 is simply the color space that the image you are trying to print is tagged or embedded with. Number 2 simply asks the question of what software should handle the color management - and here you want to choose Photoshop and not the printer (the exception to this may be if you want to use the printers built in system for printing in black and white, but that is a topic for another day).

Now, in #3, we come to the profiles printer/paper profiles we had discussed in Part III of this series. We have to choose what profile to print with, and all your icc profiles in the operating system’s appropriate color management folder will be listed in the drop down menuhere. You need to choose the one for the printer/paper combination you are trying to print with/on that you either downloaded or made with the profiler. If you are using the same brand paper as your printer (ie Canon paper with a Canon printer or Epson paper with an Epson printer) the Canon or Epson profiles should have been automatically loaded into your OS color profiles folder, which is to say that you won’t have to go to the Canon or Epson website to download them separately. In this instance I have applied the downloaded paper manufacturer’s profile for using Ilford Gold Fiber Silk paper in my Canon ImagePrograf 2000 printer.

Finally, in #4, we need to choose our rendering intent, as discussed earlier. Though there are more than two options to be had, there are really only two choices you should make for printing photos or artwork and that is ‘Relative Colorimetric’ or ‘Perceptual’, both using ‘Black Point Compensation’ (the other choices are for other uses, such as printing signage). I find that more times than not I use the Relative Colorimetric choice, but there are times when Perceptual fits my vision better. Frankly, I haven’t discussed soft-proofing, but making this choice is one of the things I use soft-proofing for. But go ahead, make a print using both and see the difference.

Now that we have made the choices in the Photoshop dialogue (you thought we were done, didn’t you :) we have to go into the actual printer dialogue for a few settings. We have to go up to #5 and click on ‘Print Settings’. Let’s do it!

Inside the Canon Printer Driver

Inside the Canon Printer Driver

First, up at #1 we have to choose what paper we are printing on. If you are printing on papers other than your printer’s brand (so called third party papers - like my Ilford Gold Fiber Silk) the profile you downloaded will have instructions as to what to choose here, as you will need to choose the same setting as the third party paper company used when they made the profile. So, for example, the instructions that came with my downloaded Ilford profile said to choose Canon Premium Semi-Gloss Paper 2 as my media choice in the driver (even though I am actually printing on Ilford paper, since the drop down choices will only encompass the papers manufactured by the printer brand). At #2 you need to choose the print quality, and if you are using a third party paper along with their downlaoded profile, the instructions will tell you what to choose here as well. Color mode (#3) is simple….the only choices are color or black and white printing. Now there is just one more thing to do…..but it is an important one. Remember up in the Photoshop ‘Print’ dialogue box we said we were going to let Photoshop manage the colors. Well, this is where we tell the printer driver that Photoshop is going to do the heavy lifting and it should just let things be and not apply any color management. If we forget to do this things can get very messy as two paper profiles will be applied and it’s anyone’s guess what comes out. OK, just click on #4, Color Settings, and we get this:

The color management part of the Canon Driver

The color management part of the Canon Driver

We want to go to the matching tab and click ‘OFF’ so that the driver keeps its grubby hands out of the color management. Clicking all your OK’s at the bottom will bring you back to the original Photoshop Print dialogue where you click ‘Print’ at the bottom right and very shortly you should have a masterpiece coming out of your printer!


So, you may be wondering, does all this work?? If I follow this path will my prints always look like the image on my monitor? The answer is yes……and no!

A print can never look exactly like an image on a monitor. For one thing, a literal exact match is a physical impossibility in that we see a monitor image using transmitted light and a paper print using reflected light. In addition, the colors we see in an image are very much affected by the color temperature of the light we are viewing them in. Finally, the color managed workflow itself is simply not perfect. However, it’s the best that we have and can get you reasonably close.

Reasonably close is the key word here. Expectations need to be managed. Think of it like this. If you implement a color managed workflow you are no longer ‘shooting in the dark’. You can get your first print to be a very good approximation to what you see on your monitor. Just don’t expect that your fits print is going to be exactly how you envisioned it based on the monitor appearance. Expect that you will need to do a bit of tweaking and adjusting to get the print to be exactly the way you want it. But you will be starting far, far closer to the finish line if you begin with a color managed workflow.


I do hope you enjoyed this this four part series and that it was helpful to you. As always, please feel free to leave any questions, comments, corrections, etc in the comment section below!

Basic Color Management For Photographers - Part III

PART III - Printer Profiling

In Part II we discussed monitor profiling and noted that it was the most important part of a color managed workflow. Today, I would like to discuss another type of profiling…….printer profiling.

Remember how, when profiling a monitor, the calibration and profiling device put together a ‘correction table’ so that colors were ‘tweaked’ before being displayed on the monitor to ensure that they appear correctly? Well, printer profiling is very similar. However, the monitor output only ends up in one one spot that counts, and that is going into our eyes and then on to our visual cortex. But, when printing, the printer output can end up on many different substrates. That is to say that we might want to print on several different types of paper, and each paper type handles and ‘displays’ the printer ink differently. The same ink will look a bit different on each type of paper it is applied to. What this means is that we actually need a different profile (or correction table) for every different paper or canvas that we want to print on. Yeah:

Image by Robin Higgins

Image by Robin Higgins

But fret not, because while I am going to tell you how it’s all done, I am also going to tell you that for basic color management you need not worry too much about it. Why? Because you can easily get these profiles made for you at no cost. I’ll tell you how in just a bit.

So how are printers ‘profiled’ if each different paper needs its own profile? Here’s how:

First, color management in the printer is completely disabled in the printer driver (more on this later, but we have to start somewhere) and a standardized set of color patches are printed out on the specific paper you would like to use. The number of patches to print can be adjusted in the profiling device software, depending on how accurate you want the profile to be, and can range from many hundreds to many thousands of small patches. Despite printing without color management in the printer driver, you still need to pick a media type in the driver in order for the printer to print. One can experiment with what to choose in order to get the best amount of ink put down (for example, matte papers take more ink than glossy papers) and the best color differentiations (like I said, don’t worry too much about this). The patch printout looks something like this:

Color Calibration Patches

Color Calibration Patches

Now, once the patches are completely dry, you take your hardware profiling device and ‘read’ the colors by scanning each patch. Yes, it’s tedious work, though there are expensive devices that can automate it for you. So, the device software now ‘knows’ what actual color the printer outputted onto the paper, and it also knows what each color patch should have been outputted as. Just like with monitor calibration, these color patches are not random….they are very specific colors and the software knows how they ‘should’ look. Just like with monitor calibration, the software can then generate an icc profile that contains look up correction tables. The profile says ‘oh yes when color x is printed on this specific paper it makes it look a bit too yellow, so when the user tries to print that color I am going to give instructions to the printer to put down less yellow in just the right amount so that the color looks right’. And it does the same for the colors of all those patches while also extrapolating the corrections for the colors that are ‘between’ the patches.

Now I have to drop something on you here….the device used to measure the color patches on paper is not the same $200 one that is used for monitor calibration. No indeed. This device is one that costs well over $1000!!

Image by Robin Higgins

Image by Robin Higgins

Remember, up above, I told you not to worry about all this? The reason you don’t have to worry about it is that paper manufacturers do this profiling for you for free. Well, maybe not for you personally, but for consumers as a whole. Why??? Because they want you to make great prints with their papers……so that you buy more paper. For almost every paper manufacturer you can go to their website and download, for free, a printer (also called paper) profile for your specific brand and model of printer to use with their specific papers.

For example, here is a screen shot of various printer/paper profiles I could download for my brand printer if I wanted to print on one of the smooth matte papers made by Hahnemuhle.

icc.jpg

These manufacturer generated profiles also come with instructions on how to install them into the correct operating system folders so that the printer knows where to look for them (but you already know the folder location if you read Part II of this series) and, importantly, they also tell you what media setting to use in the printer driver to get optimal results (the printer driver only has media settings for its own brand of paper, so the third party paper company has already figured out what setting works best for their paper and used it to make the test color patches). Now you need to replicate what the paper manufacturer did by printing your photos on their paper with the same media settings they used to make the profile.

These profiles made by the paper manufacturers are really quite excellent, after all they want you to get great results. However, while they are generated from the same brand and model printer that you have (you chose it when you ordered up the profile download), they weren’t made from color patches printed by YOUR exact printer. Yes, you can get in as deep as you’d like. I am going to say that for the vast majority of people reading this, the paper manufacturer’s profiles are really darn close enough and the whole color management thing, while really good, is never perfect anyway. BUT, if you want a profile made for your specific printer, the one sitting in your office, you can either buy the over $1000 device or, alternatively, print out the test swatches on your printer and snail mail them to someone who makes custom profiles. They will do the profiling steps described in the beginning of this post. These custom profiles can be had, at varying quality, for anywhere from $30-$75 for each paper you want to print on.

So now you know what goes on behind the scenes in making printer/paper profiles and you know how to get and install them without having to spend the time and money to make them yourself. Aren’t you glad you read all the way through : )

So how does one use those profiles now that you have them installed? That will be the subject of the next post, which will be the final one in this series.

Comments or questions? Just click on comments link below and I will do my best to answer them.

Basic Color Management For Photographers - Part II

PART II - Monitor Profiling

When we left off in Part I , we had reached the point where we could define a color within a color space, but were thwarted in our attempt to have that color look the same to different viewers using different computer monitors (think of that TV store where all the TVs are tuned to the same channel but they all look slightly, or, in some cases, vastly different).

This is where monitor calibration and profiling comes to the rescue.

My apologies to Dilbert….I changed two words in the first frame.

My apologies to Dilbert….I changed two words in the first frame.

Simply put, calibration and profiling is an attempt to standardize the appearance of computer monitors in order to avoid the “TV Store” phenomena and have a given color look the same on all properly calibrated and profiled monitors. Does it work? More or less yes. Perfection is hard to come by since different monitors have different color gamuts; meaning that some monitors can actually display more colors than others. If the monitor is unable to display a specific color it will have to somehow ‘squeeze it’ into the range of colors it can display. In addition to that, different quality monitors have different ranges of brightness and contrast that they can achieve, as well as different levels of accuracy and consistency when it comes to their displays. BUT….while calibration and profiling may not be perfect, it’s as good as we can get and it works reasonably well.

The bad news is that properly calibrating and profiling your monitor requires a device (colorimeter or spectrophotometer). Such devices are made by several companies, including Datacolor and X-Rite, but they can set you back anywhere from about $150-$1500. However, the lower price range devices work quite well and a very reasonable calibration device can be had for about $200. While there are some non-hardware based calibration methods they, unfortunately, do not work nearly as well as device based calibration. To get started with a color managed workflow, monitor calibration is your most important step and yields the ‘biggest bang for the buck’.

Profiling your monitor actually consists of two steps, a calibration step and a profiling step. Both steps are done by the same device which is hung over the top of the monitor, gently touching the screen, as shown below. An easy way to think about calibration is that it sets the baseline attributes of the monitor to a standard state. This includes the monitor’s color temperature, gamma, brightness and contrast. Once the baseline standard is achieved and the monitor has known attributes, then the colors that are displayed can be properly adjusted.

A monitor calibration device in action.

A monitor calibration device in action.

Does that seem a little confusing? Think of it like this….if you were to look at a color swatch of fabric in a dark room with no light what would you see? Right - you wouldn’t see a thing. You would have no idea what the color of the fabric is. We need light to reflect off the fabric in order to see the color (I realize this analogy is not totally accurate because monitors display color using transmitted light as opposed to reflected light…..but just go with it for now). However, the way the color looks will depend to some extent on how bright the lights in the room are and what the color temperature of the room lighting is. If we look at the swatch under incandescent lighting it will appear to be warmer in tone than if we look at it under ‘cooler’, whiter light, in which case the swatch will look more blueish. A dim light will make the color look duller while a brighter light will make it look more vibrant. So we need some type of standard lighting to look at the color swatch with. That is what monitor calibration is sort of like. It attempts to set all monitors to a standard brightness, a standard color temperature etc for viewing, so, to continue the analogy, all viewers will essentially be looking at the fabric color under similar baseline lighting conditions.

There is some argument (when isn’t there) as to what the best standard settings for use in photography are, particularly in the case of color temperature. For the most part there seem to be two camps, those that advocate setting your monitor’s color temperature to 5000K and those that advocate 6500K (I personally use 6500K). The best monitor brightness setting for matching your screen to your inkjet printer output is 80-100 cd/m2. At this setting your monitor will likely look quite a bit duller or dimmer than it did ‘out of the box’ (this, incidentally, is the most common reason that one’s prints might look too dark - the monitor is set at too high a brightness level). The gamma should be set to 2.2 (the gamma setting is somewhat akin to contrast and determines how light the lights are and how dark the darks are). But don’t worry about all this……the profiling device will do all the work of adjusting the settings for you, but you do have to tell it (in software - I once tried talking to it but it didn’t help :) what settings you want it to calibrate the monitor to……so just remember a color temperature of 6500K (or maybe 5000K if you belong to that camp), a brightness level of 80-100 cd/m2, and a gamma of 2.2.

Once the monitor is correctly calibrated it can then be profiled. During profiling, the device’s software displays a series of pre-defined color and gray-scale patches on screen, which are read by the hardware. The device measures these patches to see how they are being displayed by the monitor. The software knows what the colors should be displayed as (they are pre-defined) and how the monitor is actually displaying them (by what the device measures) and can then make a ‘correction table’ of sorts. This correction table is called an icc profile, and the software places the profile in a specific folder within the operating system. For Windows systems, the profile is located in the C:\Windows\System32\spool\drivers\color folder and for Mac OSX it is placed in either the Mac HD/Library/ColorSync/Profiles or the Mac HD/Users/<username>/Library/ColorSync/Profiles folders.

Now, when a color ‘comes into’ the monitor, like when you use Photoshop or Lightroom to view a photo (assuming that the photo has a color profile associated with it-more on this later), the icc profile basically says……OK, I know what this color is because it is defined by the color space and the RGB values and I know that at baseline I would display it in this specific way, but to display the color properly it needs to be tweaked. Let me look up in my table how I should tweak it to make it display correctly on this monitor……it then makes the tweak and has the monitor display it with the tweak applied. Does that make sense?

For completeness sake, I should mention that some more expensive monitors have a different hardware based method of profiling that may dispense with the software ‘look up’ correction profiles, but, in essence, they end up accomplishing the same thing and can be thought of in the same way.

I should also note that in order for all this to happen you have to tell your monitor that you don’t want it to use either the generic profile that came with the monitor software or the generic profile that the operating system assigns it. You need to tell it that you would rather use the profile that you generated with your profiling device. To do that you have to know what the device named the profile (it tells you and even lets you give it your own name if you would like) and you have to know how to give the monitor those directions. Here is a brief rundown of how to give those directions to the monitor for both Windows and Mac.

So there you have it…..the most important series of steps for instituting a color managed workflow.

In the third part of this series I will discuss printer profiling.

Comments or questions? Just click on comments link below and I will do my best to answer them.

Basic Color Management For Photographers - Part I

PART I - What Are We Really Asking?

Because I enjoy making prints, one of the topics that I am frequently asked about is color management. At it’s most basic level, what photographers want to know (and one of the questions that color management seeks to answer) is a query that usually goes something along the lines of:

“How do I get my prints to look the way they do on my computer monitor?”

And it frequently is asked with an expression that looks something like this:

Image by Robin Higgins

Image by Robin Higgins

And for good reason……color management can be very frustrating when things go wrong and the answers to that seemingly simple ‘how do I get my prints to look like my monitor?’ question can get complicated.

There are many places one can go to try to get answers and, hopefully, a better understanding of the process, but I have often found that the presentation of color management information is either oversimplified (just do this because it works) or over-complicated (here is a treatise on color theory). The problem is that when things are oversimplified the photographer is left doing things without really knowing why. Then, when a problem occurs (as it invariably does), they have no idea how to troubleshoot. On the other hand, when the information is presented in an over-complicated way…..

Image by Gerd Altmann

Image by Gerd Altmann

This short four part series, then, is going to be my attempt to teach the basics…..just enough so that you can gain an understanding of what’s going on behind the scenes without having your eyes glaze over…..and leave you with the ability to set up your own basic color managed workflow.

In today’s installment I would like to discuss the ‘Basic Science’ of color management. Wait…..don’t roll your eyes!!!

I see it’s too late:

Image By Robin Higgins

Image By Robin Higgins

It really isn’t difficult, and a little understanding of the terminology will be useful down the line. Sometimes you really just have to get a little more explicit about things:

cartoon 1.jpg

So let’s start by asking what one might think would be a very basic question.

What color is this apple?

 
red apple
 

“Red”, you say?

Well what about this one?

 
red apple
 

And this one?

 
red apple
 

Or this one?

 
red apple
 

Well, you get what I mean. It’s hard to define what one means when they say red. There is yellowish red, orangish red, bluish red, maroonish red, deep red, light red etc. So, when you tell me an apple is red, I might conjure up a picture in my mind of what you mean, but that picture might be very different from what you are seeing.

What is red?

What is red?

Wouldn’t it be nice if there were some way to communicate exactly what color you mean so that the red apple I am thinking of matches the red apple you are looking at. In fact, in the best of all worlds, I could convey an apple color that is exactly and precisely a specific shade of red so that everyone who heard my description ‘saw’ the same ‘redness’? That might be hard to do in our heads, but what about on our computer screens? Surely we should be able to do that!

Well, that is what color management aims to do! Is it perfect……no, but it isn’t bad and it’s the best we have to offer.

Soooo..….now that we understand why we need color management and what, at its most basic level, it aims to achieve, let’s start to examine some of the things we need to know about in order to reach that goal.

To start with, we need some definitions. Sure, definitions can be boring, but we really need them to gain a basic understanding and to get beyond ‘just do this because it works’. So here we go…..


“Color Model” & “Color Space”

We talked about ‘red’ meaning different things to different people. Well, perhaps if we could put together a reference table of sorts that might help. Then I could point to a shade of red and show you exactly what I mean. That might be as accurate as we could possibly get since we can never really calibrate the ‘wiring’ between our eyes, brain, and consciousness. The equivalent of this would be to somehow quantitate each shade of red (and every other color). This is exactly what color scientists attempted to do by devising color models and color spaces.

A “color model” is an abstract mathematical way of defining a color. In the RGB color model for instance (which is the model that one uses for computer monitors and inkjet printing), every color is represented by three numbers, one number for the red component, one for the green component, and one for the blue component. In the CMYK color model (used in most commercial printing) each color is represented by four numbers, one for the cyan component, one for the magenta component, one for the yellow component, and one for the black component.

Sounds pretty simple right? The problem is that while each color is now ‘defined’ by a set of numbers, it is still pretty abstract in nature because one could ask what those numbers actually represent? The answer is that they don’t represent anything real yet……but if we put them into a defined ‘container’ with boundaries then we can start to assign numbers and divisions to all the axes that are within that defined space. Put another way, 2 bits of red don’t mean anything until we have a contained linear red scale and can see what two bits of red look like, counting from the boundry that is 0 red and extending towards the boundry that is as red as the container holds. That is what a “color space” does. It provides the boundaries into which we fit our color model. Now those three (in the case of RGB) or four (in the case of CMYK) numbers actually mean something and define a color that we can look at.

So lets see if we can represent what I just said graphically. Here we go…..

Chromaticity_Diagram.jpg

In these graphs, the black triangles define the limits or serve as the ‘container’ of the color space. Any colors inside the triangles are contained in the color space and defined by points along the axes. All three of these graphs pertain to different color spaces that utilize the RGB color model, but they each have different sized containers to hold the colors in. As you can see, ProPhoto RGB is the largest color space followed by Adobe RGB and then sRGB. In a very real sense the ProPhoto RGB color space contains, or can represent, more colors than can the sRGB color space.


Now that we understand these definitions, we can point to a color and assign it a set of numbers that define it. Theoretically, I should be able to pull up the color space graphs on my screen and look at the exact color you are referring to and know exactly what color you mean. However…….you know how when you walk into a TV store and all the TVs are tuned to the same channel but they all look a little different??? Yeah, we have a problem! While there may be a standard somewhere that shows what RGB=0, 12, 73 looks like, the problem is that we have to look at that depiction on something and, just like the TVs, the colors on my screen don’t necessarily look like the colors on yours. So I might be able to point to the very exact spot on the graph you are referring to, but it might not look the same on my screen as yours. It therefore appears that we might have solved the color problem from a quantitative standpoint but not from a functional, day to day use, standpoint.

And now you know why monitor calibration and profiling is important. It is a very valiant attempt to solve that problem, and I will discuss that in the next post.

Comments or questions? Just click on comments link below and I will do my best to answer them.