Saturday, April 28, 2012

Color Management, the Digital Darkroom

In order to understand color management, it is important to get your hands around some of the workflow. It is also important to understand a little bit about the ICC itself. The ICC or "International Color Consortium" was created in 1993 by a number major corporations with the goal of assisting end users in creating consistent color throughout the entire reproduction process. ICC profiles are a means by which one device can translate the same color information to another. This process is applied in graphics programs like Adobe Photoshop, and created in color management systems like X-rite's Pulse or ColorVision's Spyder software.

How is a profile created?

In order to have a fully color controlled environment you must have all devices displaying or printing color, profiled. How is this accomplished? Color management software (CMS) takes readings from your specific devices and compares their color with reference files of what color "should be" as defined by the ICC. For example, to profile a scanner you would scan in what is called an IT8 target. This scan is then compared with a reference file by the CMS. The differences between what the reference file says the color should be, and what the color your device actually output is meat of the profile. Basically, a profile says what's not perfect about your particular device. If your scanner always seems to scan things in a little green, or your printer always seems to print things with a magenta cast-these are the things that are taken into account when color profiling your devices. To complicate matters a little further, this process also takes into account the differences in color between various paper and ink combinations.

Understanding Your Environment.

Color Model: When you hear the term color model we are referring to the method from which we define or classify the color we are to work with. Examples of such are RGB, LAB, CMYK, etc. Color Space: A color space is simply a variation of your color model. For instance, within your RGB framework some common variations are, sRGB, Adobe RGB, and so on. Some of these spaces are better for display e.g. sRGB and Wide Gamut RGB while other color spaces are more suited to printing e.g. ColorMatch RGB and Adobe RGB.

Now, it is important to note that every device in our workflow utilizes it's own unique color space. Meaning, while your monitor, scanner, and printer will base their color spaces basically on what we can see their actual gamut (range of colors) will differ. This is where we lose our consistency across devices. This is the problem we must attend to.

Color Management Using Adobe Photoshop: Step-by-Step

Okay, so now we're ready for the whole process-it's a big one, so keep with me. In this section I will describe how color management works with entry-level CMS's like Monaco EZ Color or ColorVision's Spyder2-programs like these >b>utilize actual hardware colorimeters for monitor calibration and a reflective target for scanner calibration. Scanning the printed target with your home scanner creates the printer profile. Entry-level programs like these generally retail between $150 and $500.

Step One: The Monitor

This step is quite easy and is generally conducted entirely in the CMS program of your choice. The CMS will guide you through the process of adjusting you monitor brightness and contrast to its proper settings and then, with the hardware colorimeter, take readings of the colors your monitor can produce. Your CMS should also set this profile as your default profile for your operating system. Take note if your CMS doesn't already explain it, you should remove Adobe Gamma Loader.exe from your Startup folder after creating a new monitor profile. AGL is a very minimal monitor correction tool and will conflict with your newly created profile.

Step Two: The Scanner

For the scanner profile you will be using an IT8 target. This is a printed color reference of approx. 250 color patches. These targets are manufactured under strict controls and are measured by ICC approved methods to produce accurate reference files. Kodak, Coloraid, and Fuji are the major manufacturers of IT8 targets and should be included with your CMS package but may be a required separate purchase. There are two forms of IT8 targets: reflective and transparent. Reflective targets create a generally consistent profile for scanning reflective images. Transparent IT8 targets are printed on to the specific film to be profiled and therefore cannot be used as globally as reflective targets.

Profiling of the scanner involves scanning the IT8 target under the same conditions that will be used to scan originals. This has to be taken to the nth degree, as every setting in your scanner software needs to be exactly the same for scanning the target as it is for every other original that you will scan. Turning all hue/saturation/brightness/contrast controls off in your scanner software generates the most effective profile. Any auto correction adjustments need to be turned off so the same conditions the profile gets generated under will apply to each consecutive scan.

At this point you will scan in the IT8 target, most likely at 200 dpi, and save the file. Some CMS's will have you scan the IT8 target out of their own interface, but I would recommend scanning the target with the same application that you will be using in the future-if possible. When scanning into an application like Photoshop, remember to save the image without any profile attached (in Photoshop when saving you will see a checkbox under Save Options>Color that is labeled ICC Profile-make sure this is not checked). Now load this image into your CMS, it will take this image and calculate the differences between what your scanner sees compared to what the colors of the IT8 "really" are.

Step Three: The Printer

Now, the last piece to the puzzle, printer targets. Like transparent IT8 targets, printer targets are more complex. Similar to film, different papers or media can produce incredibly different color results. This has to be taken into account in the profiling stage. When creating a printer profile, you are essentially creating a description of the differences between what is ideal color and what is the result of the specific paper/ink/quality setting you choose. A profile created for a professional glossy photo paper will generally not produce good results if used to print on a matte heavy weight paper. The same holds true for differences in ink or quality/speed settings.

In your CMS you should be given the option to save your printer target for printing within your chosen graphic app. If asked choose not to apply a profile when opening. In Photoshop choose File>Print with Preview. Change the Output dropdown to Color Management. Under Source Space choose Document. Under Print Space choose Profile: Same as Source. You are now set up in Photoshop to print your profile target. You aren't done yet! Now go into your printer driver software and set any color options to none, or zero, or whatever shuts off any color changes by the driver. Now print your target.

This is where professional level CMS's and entry level ones differ. At this point with the entry level you will scan in the printed target and the CMS will actually use the before generated scanner profile to correct the scan, so it can the correct your printed target. A professional level CMS will have a separate hardware device designed specifically for reading printed media targets.

Step Four: Utilizing the Profiles

Okay, now that we've created all of the profiles, time to implement them. You monitor profile should be getting applied upon startup by your operating system, so let's move on to your scanner. Scan in an image-once again using the exact same settings that were used to create the profile (other than resolution). In Photoshop choose Image Menu>Assign Profile. Then choose Profile: Your Scanner Profile. Having done all of the previous steps in Photoshop correctly, you should now be amazed at how your image colors changes to appear incredibly like the original that you've just scanned in.

From here go to Image Menu>Convert to Profile and choose working RGB from the profile selections. This will convert your document to the native RGB working space of Photoshop. When printing you will apply the printer profile by once again choosing File>Print with Preview, select Document as your Source Space (which this time should be your Working RGB space) and in your Print Space choose Profile: Your Printer Profile. Remember once again to disable any color options in your printer driver. Finally, Print!

Other Notes on Profiling

I would recommend using Relative Colorimetric as your Rendering Intent when doing the Convert to Profile step and when printing with Print with Preview out of Photoshop. Rendering intents control how the profile is applied to either the scanner or printed image. Relative Colorimetric has proven to be the best in my testing. Read the documentation that came with your CMS in order to learn more about the other available rendering intents.

Profiles are only as accurate as the CMS that generates them and the size of the targets that are used to generate them. Packages in the $150-$500 price range generally have around 75-250 patches, while $2000 and up gets you 729 patches or more. Also, the more expensive packages rely on physical hardware devices to generate printer profiles, while the less expensive packages use your scanner as the print colorimeter. In addition, the more expensive packages have numerous options for the edition of the profiles you create.

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