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isp:white_balance [2018/06/04 09:10] – created Igor Yefmov | isp:white_balance [2022/04/04 23:32] (current) – external edit 127.0.0.1 | ||
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===== What is white color temperature ===== | ===== What is white color temperature ===== | ||
- | A " | + | A " |
{{: | {{: | ||
- | When a scene is illuminated by " | + | When a scene is illuminated by " |
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 " | + | 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 " |
- | 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 | + | 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 |
- | Red channel gains are approximated by two line segments, bordering the '' | + | Red channel gains are approximated by two line segments, bordering the \(3500°K\) mark: |
- | + | ||
- | below '' | + | |
- | above '' | + | |
+ | \[ | ||
+ | R = | ||
+ | | ||
+ | 467.6 + T * 0.166 & \quad \text{if } T < 3500°K \\ | ||
+ | 82 + T * 0.277 & \quad \text{if } T >= 3500°K | ||
+ | | ||
+ | \] | ||
{{: | {{: | ||
==== Experimental data and verification ==== | ==== Experimental data and verification ==== | ||
Line 42: | Line 46: | ||
===== Practical example ===== | ===== Practical example ===== | ||
- | What does all that mean in practice? Suppose you have set up your scene with " | + | What does all that mean in practice? Suppose you have set up your scene with " |
See also [[Automatic white balance]] | See also [[Automatic white balance]] |