Section 2.3. Color Space


2.2. Device Profiles

Once you calibrate a device, you'll then want to create a profile that describes the device's range of color and tone in its calibrated state. These device profiles can communicate with other device profiles in a color-managed workflow to increase the consistency of results.

2.2.1. Output Profiles

An output profile is a characterization of the range of colors that a specific printing device and paper type reproduces. To create an output profile, a variety of color patches must be printed and measured with a device known as a spectrophotometer. The next step is to enter the data from the patches into a software-profiling application to create an ICC profile. The software compares the known color values of the patches sent to the printer to the actual colors that were read with the spectrophotometer and, using the data from that comparison, creates an ICC profile.

2.2.2. Monitor Profiles

A monitor profile is created during the calibration process with a device known as a colorimeter, which compares the values and colors that it reads to a known set of values and colors. The monitor profile (also known as the system profile) will serve as a viewing filter, allowing you to see your image data more accurately. The dynamic range, or contrast levels, of the monitor is limited by the maximum brightness that it has. Newer LCD monitors are usually brighter than older CRT monitors, and are thus capable of a wider dynamic range.

The Xrite Pulse Elite, a color spectrophotometer

Colorimeters

2.2.3. Input Profiles

Because scanners and digital cameras don't have a fixed gamut (see the next section, "Color Space"), input profiles for these devices are a little bit different than output and monitor profiles. Input profiles do, however, have a fixed dynamic range. So an input profile can characterize a device, but it is limited to the target that you use to create the profile. With scanners, this limitation is usually not a problem because you can make a target with a dynamic range and gamut of colors as good as any image that you would scan. A digital camera, on the other hand, captures colors in the real world much better than any target that could be made. The camera-profiling software has to extrapolate the colors that are outside the target's gamut. For this reason, profiling digital cameras is limited.

2.2.4. Matrix and LUT Profiles

Profiles themselves can be matrix-based or LUT (lookup table)-based, both of which include the white point of the device. But matrix-based profiles are very small, while LUT profiles are much larger and more complex. A matrix profile is a mathematical model made up of the three primary colorants of the device and some simple tonal curves, referred to as a 3 x 3 matrix. A LUT-based profile contains much more information, consisting of a table of numbers that allows you to find an input value and its corresponding output value. Matrix-based profiles are used for simpler devices, such as scanners and monitors, while LUT-based profiles are used for more complex devices, such as printers.

GretagMacbeth Color Checker SG

An IT-8 chart

There are many different color spaces available, and most of them are matrix-based. The advantages of a matrix-based profile are conversion speed and the ability to convert back and forth.

2.2.5. PCS Source and Destination

Profiles are usually used in pairs. Generally, you will go from a source profile to a destination profile. In order to use a profile to convert from one device to another, we need to go through an intermediate color space known as the profile connection space (PCS), which works like a translator, converting from one color space to another. This conversion can be from RGB to RGB, CMYK to CMYK, RGB to CMYK, and others.

THE COLOR MANAGEMENT MODULE (CMM)

The last component of a color management system is the Color Management Module (CMM), which is the engine under the hood that does all the calculations. The CMM is usually part of the operating system, but there are third-party CMMs available. The default CMMs for both Windows and Mac operating systems were developed by the same company, Heidelberg, and should perform the same on both platforms. Photoshop has its own CMM, named Adobe (ACE), that is the default within the Adobe suite of applications and can be changed if needed for a particular workflow that is directed by equipment and software interface specifics. In most cases, you do not have to set your CMM; it will use the default.





Practical Color Management. Eddie Tapp on Digital Photography
Practical Color Management: Eddie Tapp on Digital Photography
ISBN: 0596527683
EAN: 2147483647
Year: 2006
Pages: 61

Similar book on Amazon

flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net