How Color Temperature works

Summary

Calculator that measures the scene's Kelvin temperature and recommends a color-correction (CC) filter to bring it into balance with the loaded film stock. Sub-entry of CSV row 3.1; the live overlay version is at id 3.1.

How it works

Every light source has a colour, measured in Kelvin (K). Sunlight at noon is around 5500K. A tungsten bulb is around 3200K. A candle is around 1800K. Daylight-balanced colour film is made for 5500K; tungsten film is made for 3200K. If the film and the light do not match, the picture comes out too warm or too cool. This modal measures the scene Kelvin and tells you which CC (colour correction) filter to put on the lens to bring the two back into balance.

How it measures

Tap the calculator and the camera takes a quick reading of what it sees. The app analyses the colour balance of the image and converts it to a Kelvin value. The reading is most accurate when you point the camera at a roughly neutral surface (a grey wall, a white card, a sidewalk) lit by the source you want to measure.

Why the AWB lock matters

Phone cameras are constantly adjusting white balance to make scenes look neutral. While you are in this modal the app forces the camera into Daylight mode so the image comes through unmodified and the Kelvin reading reflects the actual scene, not the camera's correction.

Film balance

Pick the balance of the film you have loaded: Daylight (5500K), Tungsten (3200K), or whatever the modal supports. The recommendation depends on what you are matching to.

CC filter recommendation

If the scene is warmer than your film expects, the modal recommends a cooling filter (an 80 series). If it is cooler, it recommends a warming filter (an 81 or 85 series). It also gives you alternatives in case you only have certain filters in your bag.

Re-measure

If the light changes (clouds, the sun moves, you walk into a shaded street) tap Re-measure to take a fresh reading.