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Calibrate Your Monitor

(Originally published on Jasc website, but no longer available on-line)

To get the very best results, you need to have a properly calibrated monitor. Calibrating the monitor improves the quality of your graphics and photos, and allows others to view your images as you intend them to be viewed.

For easy, accurate and repeatable monitor calibration, we recommend using a colour calibration device such as Color Spyder, Xrite device, etc.

If you do not have one of these devices, calibrate your monitor by following the instructions for the Brightness & Contrast Calibration and the Gamma Estimation below.

Brightness and Contrast Calibration

With a properly adjusted monitor, you should be able to distinguish square 1 and 2 from square 0 and the surround for the dark squares at the top and the light squares at the bottom. All the squares in the center grayscale should be distinguishable and the steps should look evenly spaced. If your monitor doesn’t meet this criteria, it needs adjustment. Follow these steps:

  • Warm up the monitor for 30-60 minutes. Select subdued room lighting, avoiding reflections of lights or windows on the monitor.
  • Under File > Preferences > Monitor Gamma, set all three color channels to 1.00.
  • Turn the contrast control, usually a half black/half white circle, all the way up.
  • Adjust the brightness control, usually a sun symbol, until you can differentiate the dark squares.
  • If necessary, adjust the contrast control to differentiate the light squares.
  • Mark the control positions and tape the controls in place.

    • Monitor Gamma Estimator

  • Stand facing the screen. Make sure you are far enough away so you can’t clearly see the numbers in the squares.
  • Estimate which square best merges with the background and note its position.
  • Check the number in the square. This is the monitor gamma.

    • When viewing images, once the data is read from your image file, it undergoes several transformations. The last of these is the application of voltage to the electron gun in your monitor, causing an electron beam to strike the phosphors on the inside of the monitor faceplate, which then emit red, green, or blue light. The relationship of the light output to the applied voltage is roughly like the following chart.

    You can see that the light output rises faster as the voltage is raised. The shape of the curve equates to this relationship:

    Light output = Voltage

    where is the Greek letter gammaand controls how sharply the curve sweeps upwards. This type of curve is called a power law curve and results from electrostatic interactions in the picture tube. Depending on your monitor and its driver software, you may or may not be able to adjust gamma. However, you can at least check that the gamma of your overall system is in the correct range. The effect of varying gamma is shown below.

    Though monitor gamma is the most frequently discussed item in connection with monitor calibration, your monitor has two important controls that should be adjusted before you estimate your system’s gamma. These are brightness and contrast.

    You can think of the brightnesscontrol as a black levelor offsetor pedestalcontrol. Its behavior is shown below.

    The effect slides the entire curve up or down. When the curve is too high, light is emitted even when the image is black. Pure black cannot be seen and appears as a dark gray instead. When the curve is too low, even dark gray causes no light output because the monitor cannot emit “negative light”. As a result, dark grays are indistinguishable from black, so the shadow detail in your image is lost. The control should be positioned so the black is as black as your monitor can show and the darkest gray is just perceptibly lighter than this black.

    The contrast control can also be thought of as a picture or range or scale control. It raises or lowers the topmost part of the gamma curve. This is illustrated below.

    In combination with a properly set brightness control, the contrast control should be set as high as possible. This lets you see the largest range of light intensities. Under optimal viewing conditions, the human eye can discern 100 steps of lightness, provided they are of a certain size. Thus, for you to see them all, brightness must vary over a wide range. This will give your images maximum contrast and sharpness. There is, however, a practical limit to how high you can set the control. If you set it too high, you can lose the ability to distinguish light gray from white, therefore, reducing the highlight detail in your image.

    Once the brightness and contrast are set properly, you can tape these controls in place. The settings of good monitors do not drift much and should be stable for a number of months. Now you can check the gamma of your system using the gamma Estimation image (download). A properly adjusted PC system will have a gamma value in the range 2.35 to 2.55. The gamma value controls the balance between highlights and shadows in the image. Too high a gamma, and your images looks too bright with no highlight detail. Too low of a gamma, and your images looks dark and shadow detail cannot be seen.

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