3 ms·

> The transfer functions in your (rec.709) color space is non-linear indeed. However, the pixel values you store are in a linear relationship with each other. T

> The transfer functions in your (rec.709) color space is non-linear indeed. However, the pixel values you store are in a linear relationship with each other. The difference between values 20 and 21 are the same as the difference between values 120 and 121, assuming an 8bit signal. I.e., the information is the same for all pixels. Difference on what scale? ... because (hint hint) it's not number of photons that hit the sensor. Nor is it photons emitted from the display. The truth is, it's a linear measure of the voltage which drives the electron beam of a CRT. Not a very useful measure anymore, but we've encoded this response curve into all of our images and, now, this is proving to be a mistake. Working with images would be so much easier if we stored values that represent linear light (i.e. proportional to photons entering/leaving a device) with no device curves baked in. Log formats do this, but because the order of magnitude of light is more important than the absolute value, it takes the log of the value. It's a more efficient use of bits in the storage / transmission.

thrdbndndn 3y ago
Gamma curve is needed due to the fact human eyes are more sensitive to darker areas than the brighter areas (Stevens' power law), so with gamma you can get away with lower bit width without (perceptually) introducing noticeable banding. The fact it somewhat matched with a response curve of CRT seems to be a historical coincidence, based on multiple sources I've read in these years. I do agree we should have get rid of it at this point as it introduces many errors in color blending. > Log formats do this, but because the order of magnitude of light is more important than the absolute value, it takes the log of the value. It's a more efficient use of bits in the storage / transmission. It literally is what gamma curve does, ina slight different but mathematically equivalent way. "Order of magnitude of light is more important than the absolute value" is exactly what Stevens' power law describes.

thrdbndndn 3y ago

Gamma curve is needed due to the fact human eyes are more sensitive to darker areas than the brighter areas (Stevens' power law), so with gamma you can get away with lower bit width without (perceptually) introducing noticeable banding. The fact it somewhat matched with a response curve of CRT seems to be a historical coincidence, based on multiple sources I've read in these years. I do agree we should have get rid of it at this point as it introduces many errors in color blending. > Log formats do this, but because the order of magnitude of light is more important than the absolute value, it takes the log of the value. It's a more efficient use of bits in the storage / transmission. It literally is what gamma curve does, ina slight different but mathematically equivalent way. "Order of magnitude of light is more important than the absolute value" is exactly what Stevens' power law describes.