How to use it
- Choose or drop a photo; the automatic fix is applied straight away.
- Compare with the original by turning Auto levels and Auto white balance off and on.
- Lower the Strength if the fix goes too far.
- Adjust Brightness, Contrast and Saturation by hand if needed, then download.
How it works
- White balance (grey world): the averages of red, green and blue are measured, and each channel is multiplied by grey ÷ its own average, where grey is the mean of the three averages.
- Levels: the black point lo and white point hi are found from all colour values together, ignoring the darkest and brightest 0.5 %. Each value becomes (v − lo) × 255 ÷ (hi − lo).
- Strength mixes the original and the fixed picture: 50 % is halfway between them.
- Brightness adds up to ±127.5 levels (2.55 per step), contrast scales the distance from middle grey 128 by 1 + c ÷ 100, and saturation pushes colours away from (or towards) their own grey by the same percentage.
Example
A photo with averages red 120, green 100, blue 80 has a warm cast. Grey is 100, so red is multiplied by 100 ÷ 120 = 0.83, green by 1 and blue by 100 ÷ 80 = 1.25: a pixel (120, 100, 80) becomes a neutral (100, 100, 100).
If the darkest tones of a flat photo sit at 50 and the brightest at 150, auto levels maps 50 to 0 and 150 to (150 − 50) × 255 ÷ 100 = 255. At 50 % strength they become 25 and about 202.
Tips
- Use auto enhance first and do creative edits (filters, grain, effects) after it.
- Photos of snow or a white wall often come out grey in cameras; auto levels brings the white back.
- If skin tones turn too cool, keep levels on and turn white balance off.