white balance -> ισορροπία λευκού, εξισορρόπηση λευκού, ρύθμιση λευκού

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white balance -> ισορροπία λευκού, εξισορρόπηση λευκού, ρύθμιση λευκού
Spanish: Compensación de blanco
French: Balance des blancs

Color temperature is a characteristic of visible light that has important applications in lighting, photography, videography, publishing, and other fields. The color temperature of a light source is determined by comparing its chromaticity with that of an ideal black-body radiator. The temperature (usually measured in kelvin (K)) at which the heated black-body radiator matches the color of the light source is that source's color temperature; for a black body source, it is directly related to Planck's law. Yellow-red colors are considered warm, and blue-green colors are considered cool. Confusingly, higher Kelvin temperatures (3600–5500 K) are considered cool and lower color temperatures (2700–3000 K) are considered warm. Cool light produces higher contrast and is considered better for visual tasks. Warm light is preferred for living spaces because it is considered more flattering to skin tones and clothing. Color temperatures in the 2700–3600 K range is recommended for most general indoor and task lighting.

Film photography

Film sometimes appears to exaggerate the color of the light, since it does not adapt to lighting color as our eyes do. An object that appears to the eye to be white may turn out to look very blue or orange in a photograph. The color balance may need to be corrected while shooting or while printing to achieve a neutral color print.

Film is made for specific light sources (most commonly daylight film and tungsten film), and used properly, will create a neutral color print. Matching the sensitivity of the film to the color temperature of the light source is one way to balance color. If tungsten film is used indoors with incandescent lamps, the yellowish-orange light of the tungsten [incandescent] bulbs will appear as white (3200 K) in the photograph.

Filters on a camera lens, or color gels over the light source(s) may also be used to correct color balance. When shooting with a bluish light (high color temperature) source such as on an overcast day, in the shade, in window light or if using tungsten film with white or blue light, a yellowish-orange filter will correct this. For shooting with daylight film (calibrated to 5600 K) under warmer (low color temperature) light sources such as sunsets, candle light or tungsten lighting, a bluish (e.g. #80A) filter may be used.

If there is more than one light source with varied color temperatures, one way to balance the color is to use daylight film and place color-correcting gel filters over each light source.

Photographers sometimes use color temperature meters. Color temperature meters are usually designed to read only two regions along the visible spectrum (red and blue); more expensive ones read three regions (red, green, and blue). However, they are ineffective with sources such as fluorescent or discharge lamps, whose light varies in color and may be harder to correct for. Because it is often greenish, a magenta filter may correct it. More sophisticated colorimetry tools can be used where such meters are lacking.

TV, video, and digital still cameras

The NTSC and PAL TV norms call for a compliant TV screen to display an electrically "black-and-white" signal (minimal color saturation) at a color temperature of 6500 K. On many actual sets, however, especially older or lower-quality units, there is a very noticeable deviation from this requirement.

Most video and digital still cameras can adjust for color temperature by zooming into a white or neutral colored object and setting the manual "white balance" (telling the camera that "this object is white"); the camera then shows true white as white and adjusts all the other colors accordingly. White-balancing is necessary especially when indoors under fluorescent lighting and when moving the camera from one lighting situation to another. Most cameras also have an automatic white balance function that attempts to determine the color of the light and correct accordingly. While these settings were once unreliable, they are much improved in today's digital cameras, and will produce the "correct" white balance in a wide variety of lighting situations. White balance can also be corrected in post-processing in much the same way, although extreme amounts of correction will result in a loss of image quality due to color value quantization.

en.wikipedia.org/wiki/White_Balance

If you’re like a lot of people, you get your first digital camera, open up the box, take a quick look through the instruction manual, then decide that actually reading all of that garbage can wait until later, when you have the time to spare. We all know what happens next. You never have the time to spare and you discover that the "auto" settings work pretty darn well, so you proceed on down your photographic path on autopilot.

Well, in this article, we’re going to cover something that is quick and easy to master, and can help you make a big difference in your photos – white balance.

First, let’s talk about color temperature. It’s funny how our eyes adjust so well to changes in light that we really don’t notice how different light affects things. We have our own auto color balance built into our brains, basically. Have you ever been in a room with one of those red heat lamps for a few minutes, then walked out into normal lighting and noticed that everything looks totally green and weird? Then after a very short period of time, things don’t seem green anymore – because your brain and your eyes work together and somehow figure out that the light isn’t red anymore and they don’t need to compensate by “filtering” your vision with that green color-cast.
istockphoto.com/article_view.php?ID=95
« Last Edit: 02 Jul, 2008, 16:54:33 by spiros »


 

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