Color-Temperature Correction in Mireds

The mired shift that takes one color temperature to another, the standard correction sheet closest to it, and where a given sheet actually lands. Kelvin is not a perceptually even scale: going from 3,000 K to 3,200 K is a visible correction while going from 9,000 K to 9,200 K is invisible. Mireds -- reciprocal color temperature times a million -- ARE even, which is why every correction filter on the market is specified as a mired shift rather than as a pair of kelvin values, and why a full CTB is about -131 mireds no matter what it is put in front of. Once a crew is thinking in mireds, what gel gets me from here to there is a subtraction and what does this gel do to that source is an addition. Negative shifts are blue and raise color temperature; positive shifts are orange and lower it. Matching a 3,200 K tungsten fixture to 5,600 K daylight is 178.6 minus 312.5, a shift of -133.9 mireds, and a full CTB at about -131 lands within three mireds of the target -- effectively exact. Try the same correction by kelvin arithmetic and the difference is 2,400 K, but there is no gel labeled 2,400 K because the number means something different depending on where you start: from 5,600 K a full CTO lands at 3,230 K, while from 6,500 K the same sheet lands at 3,510 K. Same gel, different result, and only the mired scale predicts it. A conversion; the filter manufacturer's published mired shift for the specific sheet and a color meter govern a critical match.

source_mired = 1,000,000 / source_k; target_mired = 1,000,000 / target_k; shift_needed = target_mired - source_mired; resulting_k = 1,000,000 / (source_mired + applied_shift).

Reciprocal color temperature (mireds = 1,000,000 / kelvin) and the mired-shift specification of correction filters, by name; the full, half, quarter, and eighth CTB and CTO shift values are the conventional nominal figures, and the filter manufacturer's published mired shift for the specific sheet, plus a color meter, govern a critical match.

The mired conversion is public colorimetry. The nominal correction shifts are the conventional published figures, cited rather than reproduced from any manufacturer's swatch book.

Estimate. AHJ and licensed professional govern.

Field names used by the API: source_k, target_k, applied_shift, source_mired, target_mired, shift_needed, resulting_k

• Mired scale 1,000,000 / kelvin; perceptually even, which kelvin is notpublic colorimetry
• Nominal sheet shifts full CTB about -131 and full CTO about +131 mireds, with half, quarter, and eighth in proportionconventional correction-filter figures
• Critical match the filter manufacturer's published mired shift for the specific sheet, and a color meter, governfilter manufacturer data