It is what you see on-screen that allows you to perceptually adjust and change a digital photograph. I have said what I believe to be true, if you can’t see it, you cannot control it. So I have thought of all things computer, the display is the most important part for digital photographers. However, some think I make too much of it, but then the display gets me more questions in my mail than any other subject.
Some of those questions of late have me wondering what worse related to the color management of a computer display than misunderstanding terms like calibrate and profile. So let’s begin with what comes in a box that contains a new LCD display. It is much like a new car from a factory delivered to a dealer. Before that car can be sold and put in the hands of a new owner, it must be prepared by the dealer’s mechanics, it needs among other things its first tune-up. In other words many products out of the box from the manufacturer are within production allowed tolerances. But is that enough for them to run efficiently and effectively for the user. All mass production makes items that vary from ideal specifications a little. So to get the best they can offer in performance, adjusting them to that ideal is a significant advantage in the accuracy of what the product does.
LCD display calibration is done with one of several brands of display products that includes a measurement instrument, a colorimeter, or what some call a “puck”. This device in use sits on the front surface of a display and reads the color values of the target samples the software that comes with the colorimeter generates. And, those colors are the values as defined by the ICC, the International Color Consortium; in other words the internationally accepted standards for computer color.
All display color management products that are on the market that have a colorimeter and software do two basic things, produce a calibration file that is part of the computers boot-up procedure; and it also produces a detailed color profile file that describes the displays color reproduction over a wide range of color differences within the visible spectrum. In addition some display color management software products also provide a measurement and display of the display’s white luminance, how bright the display is adjusted to reproduce white.
The calibration executable file and the profile file are two different kinds of files in two different locations in your operating system. The calibration file contains the basic variations from the ICC standards so the display is then adjusted through the computer’s video card to conform to the ICC standard color performance. The calibration file is an executable file that is placed in the computer’s start-up folder and adjusts the color performance of the display every time the computer is started and booted-up to run the operating system.
Each display has its own unique color reproduction characteristics in addition to the basics defined by calibration. These are measured in detail by the colorimeter reading a large number of color target patches reproduced by the display profiling software from the colors defined by the ICC standard, and any differences the display reproduces are noted in the profile file produced. In other words the profile file created by display color management software is a description of how much the display being measured varies from each color in the ICC standard. So, it is a color description of that display’s color reproduction performance.
What does calibration and profiling do for the photographer using a computer? First, without calibration and profiling a computer is blind to the pictures it is reproducing on-screen even though it knows the RGB values in the file being reproduced, but it does not know how they look on-screen. The result is then if you use any image editing software that is color managed, like all Adobe versions of Photoshop, LightRoom as well as iPhoto or Aperture on an Apple Mac, or even PaintShop Pro from Corel for a PC, the application does not know what you are seeing on screen without calibration and display profiling. Nor does one of those applications know what color values are in the image files that are sent to a printer for reproduction. In other words without display calibration and profiling everyone is color-blind, you and your computer, to the images being reproduced and used. Likewise, if the profile of the workspace, like sRGB or Adobe RGB are not imbedded in saved files sent to anyone else, like a print service then the recipient is blind to the color in the image file received. The result is color reproduction digitally then becomes nothing more than a guessing game.
Wouldn’t you rather know what you are doing, and seeing the real color values of your photograph on-screen?