Above is an equi-stepped greyscale at 4% intervals starting from A, the brightest possible shade (white), and descending to Z, the darkest possible shade (black). If your computer monitor (screen) is set up correctly, then you should be able to discern differences in brightness between A, B and C, and at the same time distinguish different shades of darkness in X, Y and Z. If you cannot, then your monitor is set up in-correctly and any photographs displayed on your monitor (either from this website, or from your own digital camera) will be shown with either washed out highlights, or like black cats in coal cellars, or both.

Left is a 50% grey square surrounding a 2x2 pixel checker-board grid of squares alternately 12% white and 88% black (represented by squares 'D' and 'W' in the above grey-scale). If viewed from far enough away (or squint at it), the two areas, inner and outer, should be perceived as being of equal greyness. If not, the gamma adjustment in your computer may require adjustment. Adjust until you can barely distinguish inner square from outer. Successfully performing this adjustment anchors the mid-point of the brightness scale to mid-grey. The author has chosen a 2x2 pixel array (rather than a 1x1 pixel array) to reduce the effects of dot-gain, a deficiency in monitors. The author has also chosen a 12%/88% dark-grey/light-grey pattern (rather than a 0%/100% white/black pattern) to try to eliminate the effects of any clipping or non-linearity in the intensity curve of your monitor at the two extremes of its brightness range, full-white and total-black. This should increase the accuracy of the test at the expense of a slight reduction in sensitivity.

Please perform any adjustments in a darkened room. If you have the lights on or sunshine is pouring into your room, you may not be able to perceive any differences in the darkest shades at all, even if your monitor is actually displaying differences.

Most computer plus monitor combinations are not set up correctly for showing digital photographs at their best, they are set up for showing Windows OS start-up screens in shops at their best to entice your purchase. The contrast is usually set up too high, and the colours too saturated.

LCD monitors are the most difficult to set up, for they are notorious for both the brightness and the contrast varying from top to bottom and from side-to-side with viewing angle. But every monitor needs a warm-up time of 30 minutes before any attempt is made to adjust them. The old LCD monitor in use here, from cold, starts off over-bright, with no difference between whites A, B or C, and takes fully half an hour to warm up and normalise. The new one does not appear to suffer noticeable temperature dependence.

To tweak your monitor perform all adjustments in a darkened room. Start by turning down the brightness and the contrast on the monitor to minimum.

Now turn up the brightness of your monitor until you can see a difference in shade between Y and Z black rectangles. Now turn the contrast control of the monitor until you can see a difference in shade between A and B. This is an iterative process and further tweaks to both brightness and contrast may be necessary before you procure an even-tempered grey-scale.

If you still cannot achieve the desired grey-scale it may be necessary to adjust the gamma control in your computers control panel, which is to be found in the display settings. Please make a note of what they were set to before you start twiddling, so that you can return to those setting if you find you are making things worse.


To access much better control over gamma and colour, those with so-called 'PCs' should go to:

  • Control Panel
  •   Display
  •     Display Properties
  •       Settings
  •         Advanced
  •          (your graphics card) [e.g. GeForce FX Go5200?]
  •            Colour Correction

[no wonder most people fail to find this, it took the author an hour of blundering around to re-find it].

Where the following slider bars will be found:

  • Digital Vibrance (whatever that means) [med]
  • Brightness [100%]
  • Contrast [95%]
  • Gamma [r,g 0.91; b 0.81]
  • Image Sharpening [off]

Variation of the above sliders (except digital vibrance) is displayed graphically on an input/output transfer function chart. It seems to the author that 'digital vibrance' is amplifying the differences between red, green and blue channels, thus affecting the saturation of mid-tone hues. Though why on Earth this is not also shown on the input/output transfer function chart is beyond me!

The sliders also directly affect the screen colours and contrast displayed. Just what is needed for fine control.

[The values shown in brackets are what the authors' 'PC' monitor is set to, which may differ from what is best for your monitor].

[The author himself prefers not to inflict upon himself the sluggishness of the interface that Windows OS computers offer, but prefers the immediacy of response offered by the RISC OS graphic user interface, which even at the meagre clock-rate of 600MHz out-performs a 3.2GHz Windows offering in terms of responsiveness, if not performance. 'Program not responding' and 're-boot computer' are not in its vocabulary].

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