Many photographic clubs now have digital projectors. Some clubs will have been using them for some time but there seems to be a lack of understanding of the process of adjusting projection systems to get the best results. As a starting point, (and this is just the start), whether you are dealing with a monitor or a projection system, it is a good idea to adjust the brightness (black level) and contrast (white level) using a suitable test card. I get the impression that many people, who a few decades ago were happy twiddling these controls on their TV sets, are afraid of the new technology - or perhaps they just can't find the knobs. Or perhaps they just can't find a test card.
Click here for full size image |
Click here for full size image |
1. Colour steps - From 0% (black) to 100% (white, red, green, blue) in steps of 5%
A difference in luminance should be visible between every step. If there is no difference between the 0% and 5% steps the Brightness of your monitor or projector needs increasing, or perhaps the ambient light level is too high. When adjusting Brightness and Contrast make sure to retain a difference in tone at the top end between 95% and 100%. This test card is not intended for adjusting colour saturation or colour balance.
2. Shadow and highlight test - Steps of 4 digits (about 1.5%) from black (0) and from white (255)
This test card allows closer inpection of shadow and highlight performance. There should be visible dark, but not black, patches labelled 4, 8, 12, 16, and distinctly different light patches labelled 239, 243, 247, 251.
I'll be happy to grant permission to reproduce these test cards on your website if you e-mail me, give me credit and a link to this page.
Colour Management, Colour Spaces and Colour Profiles
The test cards shown above do not have colour profiles and are intended for any colour space. The steps in the colour card increase in equal amounts, based on 0% = 0, 100% = 255 (in theory each 5% step should be 12.75, in practice some are 13 units, some are 12). If you are setting up an sRGB system that is not "colour aware" use the images as they are. If your system is "colour aware" attach the profile of your choice in Photoshop. (see below for how to do this).
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This Useful Test Image is available as a free download from inkjetart.com Originally compiled by PhotoDisc Inc., this file is intended for the Adobe RGB (1998) colour space, but the file does not have an embedded Adobe RGB (1998) profile. To display it correctly, therefore, you must do one or other of the following: If your system (monitor or projector) is "colour aware", (i.e. it handles embedded profiles and converts if necessary for display), open the downloaded file in Photoshop and go to Edit - Attach Profile and select Adobe RGB (1998). If your system (monitor or projector) is operating in the sRGB colour space, open the downloaded file in Photoshop and go to Edit - Convert to Profile and select sRGB (select 'perceptual' rendering intent). |
Measurement of gamma
This is the logical next step. See Technical Note 3.
© John Widdall 2008
