Photography Blog-Note

A camera chip performs the digitalization in the RGB color space. This is the color space of light in which the human eye breaks down the colors it sees into red, green and blue elements, before our brain puts them back together again into a perceived color.

The picture viewed thru a monitor, which also displays colors using the RGB model, looks different because this device cannot display as many shades of color as the camera chip can capture. And … if you send the photo to the printer, the result will be slightly different! This is due to the fact, that the printer doesn’t expose the paper so much as cover it in drops of four, six, eight or more ink colors.

For basic Web viewing and non-critical printing is not a problem. But, calibrating and profiling your monitor is the first, and perhaps the most important step in setting up a digital workstation.

The monitor image is the only view you have of a digital file, and the quality of all image retouching depends on how accurately the monitor displays it.

The cost to do this, ranges from free to very expensive.

If you want more technical informations on Gamma & Colors, I recommand you read these two excellent FAQ from Charles Poynton:

• GammaFAQ (PDF File)
• ColorFAQ (PDF File)

Controlling!

This procedure is very basic and it was not be considered as a calibration procedure! It’s just an indication to improve your viewing experience. If you can already distinguish between all distinct shades on the greyscale below, do nothing. The leftmost bar is pure black, the rightmost bar is pure white.

If it’s not the case, you must do some adjustments, use the buttons on your monitor:

1. turn the contrast all the way up (100%)
2. turn the brightness all the way up (100%).

Now, whilst watching the greyscale, turn the brightness back down to the point where you can still just distinguish between the two rightmost and the two leftmost bars. You may not be able to achieve this fully on all monitors; try to get as close as you can. In many cases, between 90% and 100% works best for contrast and between 50% and 100% for brightness.

Black Point Check

This test is based on Bruce Fraser’s work to determine if the monitor black point is set correctly. It ramps the monitor output up in steps of 1 RGB unit (beginning at pure black: RGB = 0, 0, 0). Each following step increases the output level by one unit.

A top quality monitor highly calibrated can show the difference between levels 0 and 1.

• Average monitors will not show any increase in output until level 5 to 8.
• If you do not see anything until level 11 or 12, either your monitor needs to be calibrated again using a higher black point or your ambient lighting is too bright.

On a CRT monitor, the black level can be adjusted directly using the Brightness control. On LCD systems, the only hardware adjustment is the backlight. Increasing the backlight luminance increases both white and black levels. A balancing act may be required with less capable calibration systems.

Pay attention to your ambient lighting:

• CRT monitors need a darkened room for top performance.
• The higher luminance of LCD screens gives more flexibility here.

If all the lower steps are visible but no difference is seen between steps, the screen brightness or calibration point is set too high. Do not be surprised if your monitor can not show the darkest patches or if several successive steps appear equally bright. Only the best monitors that are also well calibrated will distinguish between all patches. As mentioned above, a typical monitor in a dimly lit room will not show anything until level 5-8.

Adobe Gamma Tool

The most basic calibration tool, other than ignoring calibration altogether, is Adobe Gamma. This is certainly better than nothing, but leaves much to be desired. The sole advantage is that it is free (once you purchase Photoshop).

Before starting calibration, turn the monitor on and leave it for at least 30 minutes before any adjustments. Then, open the Adobe gamma control panel, and select the stored monitor profile that appears to match your monitor closest from the list in the load menu.

Adjust the monitor’s contrast control to maximum, and set the brightness control so that you can just discern a difference between the two centre squares. You have now set the dark point of your monitor.

Second step, enter the phosphor setting best suited to your particular monitor if you know it. The menu gives a choice of a set of pre-defined phosphors or you can contact the monitor manufacturer and obtain the x-y r, g and b numeric values. These can then be entered in the custom phosphors dialogue box.

The next menu allows you to set the mid-tone values. These should always be set on a colour by colour basis, so make sure the view single gamma only box is unticked. Red, green and blue squares are provided, and a slider under each square should be adjusted until the centre square disappears. With this done, the monitor gamma should be entered in the panel, either Macintosh default (1.8) or Windows default (2.2) depending on the platform.

Next, make sure your white point matches that of your monitor. This is when equal values of red, green and blue at full intensity produce white on your monitor screen. This is a pre-set value for all monitors, and is usually a choice of standard CIE colour temperatures. Generally, setting the Mac or Windows defaults will be OK, however the Adobe gamma control panel will allow the white point to be measured approximately.

When complete you see a screen that lets you view the monitor before and after calibration has taken place. Click on the before and the after circles to see the difference. If it looks right click on finish if not click on back and re adjust.

Hardware method

Physical calibration devices provide you with the most effective way (and expensive) to calibrate your computer. These devices are placed against the computer screen, and help adjust your colours to a recognized standard.

Some devices for calibrating listed here:

• ColorVision Spyder System
• GretagMacbeth Systems
• ColorEyes Display

For my work, I use the ColorVision SpyderPro from ColorVision. If your photography requires excellent shadow response or superb B&W performance, the SpyderPro is ideal. The included software offers the most flexibility of any of the recommended systems.

Tips and hints

Regularly degauss screen
Most CRT monitors need to be regularly degaussed. A monitor that needs degaussing often has subtle colour shifts across the screen. It is usually an option on the control panel on the monitor, although some monitors always degauss themselves when first powered up. Remember to do it once a week and always before calibrating the display.

Regularly clean your monitor screen
It’s sometimes surprising how quickly a film of dust can collect on a monitor screen. At least once a week give the screen a clean.

Don’t let stray light fall onto the screen
Try to position your monitor so that stray light doesn’t fall on the screen and spoil the contrast of the screen or give distracting reflections. A thin black card hood can greatly improve display quality for little cost.

Social Bookmarking