Light and shadow: optimize contrast, brightness and color

Who enters the open day from a brightly enlightened room in a cloudy day, hardly realizes that the brightness is suddenly rising on tenfold and more, because the human eye adapts very quickly to a wide variety of lighting differences. It works in a light-flooded snow landscape with more than 100.000 lux and can detect something even in a star clear, moonless night at 0.001 lux.

The contrast is the cause of dafur that troubles daylight is sometimes darker than an enlightened buro, though it is the other way around. On a trust, maybe even foggy day, the brightness differences between the darkest and the brightest details are quite low. In a room with artificial light, however, there are usually deep shadows and thus more contrast. Already the old flamic champions have known that they bring with dark backgrounds more liked light into their paintings. Bright skin flakes and painted candle flames seem to light up in these images.

Modern cameras adapts thanks to bulltered exposure meters expansive quickly and exposure time to different brightness. However, the contrast scope detectable by a sensor generally includes a maximum of nine aperture levels. In the case of the brightest point of the motif 29 = 512 times as much light as of the darkest. However, a scene in the sunlight, however, is already clear to this bandwidth. The episode: depending on the concrete exposure setting, either the shadows are underexposed and thus black or bright images like the sky are covered and thus to a contourless soft flat.

In the film negative, the transition to over- or underexposure extends soft, so it can often be fooled out of incorrectly illuminated negatives yet details. Similarly, the digital photo allows highest in underexposed areas, and this only for the price visible noise. The conclusion: underexposure may be bad, overexposure is absolutely prohibited. How to avoid overexposures, is in the following chapter.

The jpeg format used by compact cameras stores 256 brightness levels per rgb color channel. The mixture gives the famous "true color" of 256 × 256 × 256 = 16.7 million colors. The contrast between the smallest and the coarse brightness value is only 1: 255, ie about eight apertures.

Light and shadow: optimize contrast, brightness and color

The starting photo lacks mittelons. The automatic contrast balancing of photoplus raises the shadows too far.

This dynamic compression is quite intentioned, because for the presentation on a good monitor, 256 brightness levels range. Depending on the color and paper quality, prints have even lower contrasting. It only depends on the fact that the fine brightness differences are preserved in the subject (the detail drawing) – both in the dark and the bright image areas. Unfortunately, it often happens that pictorial details slip on the lower or upper end of the dynamic circumference and remain largely empty the middle. In the histogram, this shows in two mountains with a deep valley in between.

Such a faulty contrast can be compensated manually. Many programs, including photoplus, have an automatic, which stomps the contrast into the converting brightness areas. In the picture shown above the park area concerns this especially the shadows. Each contrasting in a brightness area causes contrast reduction in other areas. Another, better controllable method must be.