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isp:white_balance [2019/05/09 00:54] – [Practical example] Igor Yefmovisp:white_balance [2019/05/09 00:55] – [What is white color temperature] Igor Yefmov
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 ===== What is white color temperature ===== ===== What is white color temperature =====
-A "white" color has different chromatic characteristics, depending on its "temperature". That temperature is traditionally expressed in Kelvin and corresponds to light, emitted by an ideal black body radiator, when heated to that temperature. Think of it as the color of a burning stick of wood at a camp site or a "red-hot iron" that looks more yellow when it actually melts in a furnace.+A "white" color has different chromatic characteristics, depending on its "temperature". That temperature is traditionally expressed in Kelvin and corresponds to light, emitted by an ideal black body radiator, when heated to that temperature. Think of it as the color of a burning stick of wood at a campsite or a "red-hot iron" that looks more yellow when it actually melts in a furnace.
  
 {{:isp:color-temperature-1500x600.jpg?600|}} {{:isp:color-temperature-1500x600.jpg?600|}}
  
-When a scene is illuminated by "white" color there's usually color correction needed to bring the "true" colors out. The "true" in this sense is an approximation of how our brains perceive colors during daylight, which is around ''6000''°K.+When a scene is illuminated by "white" color there's usually color correction needed to bring the "true" colors out. The "true" in this sense is an approximation of how our brains perceive colors during daylight, which is around \(6000°K\).
  
 For our purposes, we are using individual color channel **gains** to compensate for a given temperature. Lower temperature "white light" needs a lot of blue added to it and very little red and as the temperature climbs up, the amount of added red grows while the added blue goes down. For our purposes, we are using individual color channel **gains** to compensate for a given temperature. Lower temperature "white light" needs a lot of blue added to it and very little red and as the temperature climbs up, the amount of added red grows while the added blue goes down.
 ===== Color correction for white temperature ===== ===== Color correction for white temperature =====
-For the calibration purposes we have acquired a Philips "Hue White and Color Ambiance A19 LED Starter Kit" that allowed us to test various illumination scenarios for a range of color temperatures. For a given white color temperature setting we have dialed the red and blue gains to make the scene "white" (leaving the green gain at its constant value of ''1024'').+For the calibration purposes we have acquired a Philips "Hue White and Color Ambiance A19 LED Starter Kit" that allowed us to test various illumination scenarios for a range of color temperatures. For a given white color temperature setting we have dialed the red and blue gains to make the scene "white" (leaving the green gain at its constant value of \(1024\)).
  
 Corrections to the red channel were way more noticeable than those to the blue one so we approximated the blue gains' graph with a single line, described by the formula \(B = 4205.4 - T*0.4087\). Corrections to the red channel were way more noticeable than those to the blue one so we approximated the blue gains' graph with a single line, described by the formula \(B = 4205.4 - T*0.4087\).

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