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What The Strength Slider Mixes

Guide

What the strength slider mixes

Strength is not a second, weaker recipe. It is a straight line between your photograph and the fully graded one — and where that line is drawn changes the answer slightly.

A mix, channel by channel

Every look here is a colour table: a pixel goes in, a graded pixel comes out. The strength slider takes those two values and mixes them. At 40 per cent the result is 40 per cent of the way from the original value to the graded one, separately for red, green and blue. At 0 the picture is untouched; at 100 it is the full look.

The mix is done on the values as the file stores them — gamma-encoded sRGB — because that is where the grade itself is done. One space, one straight line, no round trip. It also means strength behaves the same way in the preview, on the light table, in a batch and in a .cube saved from the recipe, where strength is baked in.

The other choice: mixing in linear light

Light adds up in linear units, not in gamma-encoded ones, so a mix done after decoding to linear light is the more physical blend. It lands on a different midtone. Here is Bleach Bypass at 50 per cent on four reference colours, mixed both ways (0–255 per channel):

ColourOriginalFull look50% in sRGB (default)50% in linear light
Skin214, 163, 135208, 183, 166211, 173, 151211, 173, 152
Sky92, 143, 209116, 146, 182104, 145, 195105, 145, 196
Foliage77, 117, 5684, 108, 7480, 113, 6580, 113, 66
Deep shadow26, 23, 2011, 11, 1218, 17, 1619, 18, 16

The differences are a few levels per channel and largest in the shadows, where the gamma curve is steepest. Both answers are defensible. The sRGB mix is the default; the linear-light mix is a switch under Base look in the workspace (“Mix the strength in linear light”), off until you turn it on, and it is saved with the recipe, so a link, a batch or a .cube made from it uses the same mix.

Using strength well

Film looks earn the most from it: somewhere between 35 and 60 per cent you usually keep a look’s character — how it treats skin, which way its shadows lean — without the cast that announces a filter. On the light table, drag across each cell to give four looks four different strengths and judge them together.

  • Strength mixes the base look only. Tone, colour, toning, HSL, curves, duotone and effects sit on top at their own values.
  • A mix cannot recover anything the full look clipped and the original did not; it only moves toward the original's value.

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