Image Color Filters

It uses the ITU-R BT.601 luma formula, a broadcast-television standard: gray value = 0.299×Red + 0.587×Green + 0.114×Blue. Green contributes the most because human eyes are most sensitive to green light, and blue the least, which is why a pure green and a pure red of the same brightness convert to noticeably different shades of gray.

Unlike grayscale, which reduces every pixel to a single brightness value, sepia uses three separate weighted formulas, one for each output channel, that consistently produce more red and green than blue. That imbalance (more warm light, less cool light) is what produces the classic warm, brownish antique-photo look instead of a neutral gray.

It limits each color channel to a fixed number of possible brightness steps instead of the normal 256. At 4 levels, for example, every red value in the image is rounded to one of only 4 possible reds, producing flat bands of color instead of smooth gradients, the classic "poster" look. Lower numbers produce a more dramatic, blockier effect.

Solarize only inverts the pixels that are already at or above your chosen brightness threshold, values below the threshold are left completely alone. That selective inversion is what recreates the classic darkroom "solarization" (Sabatier effect) look: shadows and midtones often stay normal while highlights flip toward their negative, producing a mix of positive and negative tones in the same image.

It blends between your original image and the fully-filtered result, 0% shows the untouched original, 100% shows the full effect, and anything in between mixes the two proportionally. This lets you dial in a subtle version of an effect instead of only being able to apply it at full strength.