Understanding Surround Effects
One of the factors that affect the perception of an image is the content of the area surrounding it. In the example below, the center patches of the color have the same value (128 128 128 RGB) yet the left patch appears to be lighter than the one on the right.
Adding articulation increases the strength of the effect.
But what happens when we test real world images, not just patches of color? The example below show that surround effects seem to be weak or non-existent on real world images. Certainly the difference is nowhere as dramatic.
It seems that visual cues within the real world image overrides or overshadows the surround effects in this case. In my opinion, these examples show that surround effects *do* matter- but not so much for real world images. For an ideal monitoring environment, you should try to setup a proper surround anyways as it does matter in some situations and it is not very difficult or expensive to achieve.
For more information on surround effects, see Edward H Adelson’s Lightness Perception and Lightness Illusions.
One area where surround effects make a big difference is when evaluating the black level on LCD monitors. Almost all LCD monitors cannot reproduce true black and have a raised black level. In a dark room, they will have a “glow in the dark” appearance to them. The image below shows the LCD on a Macbook Pro.
In a brightly lit environment (i.e. the surround is bright), the black level on a LCD appears to be better even though the inherent black level of the display is still the same. Unfortunately this effect cannot be reproduced here, but you can walk into any computer store and see that LCDs do not have a glow in the dark appearance in brightly lit environments. They simply don’t look like the image above. You can still see that the black level on the LCD is raised (e.g. when screen is powered on/off, forcing the backlight off). Nonetheless blacks appear to be richer if the display is in a bright environment.
This effect is something to watch out for when considering displays as the display can be made to look better by placing it in a bright surround. If you need to monitor on a LCD display, then it can be useful to avoid a dark surround as it will make the raised black level on the LCD look even worse.