If you look at the exact same image on different monitors, it will look different on every one. This is because each monitor is unique in the way that it displays color. Color Management Scientists, engineers, and software developers have gotten together to try to mitigate this problem. They have come up with a system of color management. It attempts to keep colors consistent across a variety of display devices. This is done by characterizing how an individual device displays colors, and then calibrating it to a standard. Once a device is calibrated, a software profile is created for it that describes how it displays colors. The colors in an image file are represented by numbers. Each display device takes these numbers and turns them into colors. By comparing what colors these numbers are supposed to look like compared to what they actually look like on a given device, the color management system can act like a universal translator, and correct the display so the colors look correct. This is, of course, in theory. When color management is implemented correctly, it can work well. However, in the real world, it frequently fails for several different reasons. The first is because it is complicated. Most people have never even heard of it. Of those who have, many do not use it correctly.
The second reason is because it really requires hardware calibration devices that cost money and which the overwhelming majority of people don't have. The third reason color management doesn't usually work is because most computer monitors are not that good. LCD monitors are fairly poor in the amount of colors that they can display. CRTs were better, but they are simply not being made anymore. LCDs are usually adjusted too bright. Most laptop displays are notoriously poor at the accurate display of color. They may look good for web browsing and email, and general programs and games, and they may look fine when viewing a movie on a DVD, but this does not mean that the color they display is accurate. Color Spaces Most camera manufacturers and software developers try to allow users to work within a system of color management. To do this, they use some standard definitions of color, called color spaces, that everyone can use. The most common color space is called sRGB. sRGB stands for "Standard RGB", or Standard Red, Green and Blue. sRGB attempts to be the lowest common denominator that will work on most monitors. DSLR camera manufacturers usually give users the choice of two color spaces to use in the camera when they shoot JPEGs - sRGB and Adobe RGB. Adobe RGB is a more sophisticated color space for advanced users. Almost all cameras come with sRGB set as the default and you should leave it there unless you really know what you are doing. If you have an advanced image processing program that works with color management, be sure to set it to sRGB also. Most daytime image processing programs now support color management but some astronomical image processing programs do not. The very latest version of the Firefox web browser has color management, but it is turned off by default. Safari on the Mac uses color management. Most programs and operating systems default to sRGB as their color space. Hardware Calibration The correct way to calibrate your monitor is with a hardware calibration device like a Xrite Eye-One Display LT Monitor Calibrator, or Spyder2express Color Calibration System. If you work in color professionally, you should already have one of these. If you really are a perfectionist about your hobby of photography, you will want to get one, they are not that expensive. However, most people do not have a hardware calibration device. If you don't have one, don't worry about it, but at a minimum, you should adjust your monitor's brightness and contrast with a grayscale step wedge. Grayscale Step Wedge Adjustments A grayscale step wedge is simply a series of 18 blocks of different tones that run from black to white through the various shades of gray in between.
Adjust the brightness and contrast of your monitor so that you can see each step separately. Pay more attention to the black steps here. The darkest step should be as dark as you can make it while still being able to distinguish it from the next lighter step. You can copy this one by right clicking on it and choosing "Save Image As". Then you can place it on your web pages with your images. Ask visitors who view your images to adjust their monitor based on this same step wedge. Then you will at least have some chance that they will see something similar to what you are seeing, at least in terms of brightness of the images. Web Page Backgrounds for Image Display Images will look very different depending on the color and brightness of the of the background that the image is displayed on, i.e., the web page background. A very white background will wash out colors in an image and make it look too dark. The actual colors in the image are not changing, but our perception of them is, because it is influenced by the background. For astronomical images, to best preserve the perception of dark faint detail, it is best to use a very dark gray, or black, web page background. Do not use brightly colored web page backgrounds. Unfortunately, for reading text, a white background with black text is best. That's why most of the pages of this book are white. But for the image gallery, to best display the images, I have used a black background.
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