Exposure vs Brightness: the visual version
Every widget from the article Exposure vs Brightness: what Affinity Photo does to your pixels, in one place, for when you would rather play than read. Under each heading is a short note on what that widget illustrates. Everything is measured from Affinity Photo 3 on 8-bit sRGB images.
- Feel the two sliders
- A stored value is not light
- Adding the same number is uneven
- Exposure
- Brightness
- What they do to a color
- Gamma, the alternative
- The curves side by side
Feel the two sliders
Both sliders make the photo lighter, and they look almost the same. Push both up and watch the bright parts and the colors: that is where they differ.
A stored value is not light
A pixel stores a number from 0 to 255, not an amount of light. A stored 128 is only about 22% of the light of 255, so doubling a number does not double the light.
Adding the same number is uneven
The same number added to a dark pixel and to a bright one. The dark pixel gains several times more light. This is why a tool that works on the stored numbers (Brightness) and one that mimics light (Exposure) part ways.
Exposure
Exposure multiplies every channel and cuts off at 255. On the orange pixel, red clips first and the color slides toward yellow. On the photo, the histogram shifts right and piles up at the end, the curve is a straight line that hits the ceiling, and the clipped share grows.
Brightness
Brightness is a curve with fixed ends: black and white stay put, the middle is lifted most, and the highlights are squeezed together instead of cut off. It only has nine measured positions, so the slider snaps to them.
What they do to a color
The same dark teal in both. Exposure scales the channels, so the proportions between them hold and the hue stays. Brightness bends the curve, lifts the dim channels more, and the color moves.
Gamma, the alternative
Levels gamma, where below 1 is lighter in Affinity. It keeps black and white fixed and lifts the shadows most, which is why it opens up a dark screenshot without pushing the bright parts into white.
The curves side by side
The same photo with the curve and histograms shown. Exposure is a straight line that runs into the ceiling. Brightness bows upward in the middle. The scales are not the same thing, so the two sliders are not linked.
For the reasoning, the measurements and what I use in practice, read the full article.