Why do digiKam and LibRaw/dcraw_emu produce different RAW colors with similar settings?
Asked 7/16/2021
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2 answers
0
I converted the same RAW file in digiKam and with LibRaw’s command-line tool (dcraw_emu). In digiKam I left conversion settings at default/disabled as much as possible (gamma 1.0, no auto brightness, camera white balance, no exposure correction), using a custom input ICC profile and Adobe RGB as output. In dcraw_emu I used options intended to match that: -4 -T -w -p custom.icc -o AdobeRGB.icc.
Even so, the LibRaw output looks flatter/washed out, while digiKam’s output looks brighter and more saturated. If both use LibRaw internally, why don’t they match?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
4y ago
2 Answers
1
The washed-out colors of LibRaw point to the output image being in linear color space without any gamma correction. Digikam obviously has gamma correction applied to the image. Note that most color spaces define a gamma correction function, which is usually close to gamma 2.2
This corresponds to how data are stored in a RAW file and the sensitivity of our eyes to distinguish colors at different luminance levels. If you want to read more on this matter, I suggest starting here: What is the purpose of gamma correction in today's screens and how does it relate to graphics and photography?
Originally by user105048. Source · Licensed CC BY-SA 4.0
user105048
4y ago
0
Generated from our catalog & community — verify before relying on it.
The most likely reason is gamma/tone handling, not RAW decoding itself.
A washed-out LibRaw result usually means you’re seeing a more linear rendering with little or no gamma correction applied. RAW data are essentially linear, but images intended for normal viewing usually need a display-oriented tone curve/gamma (commonly around 2.2 or the color space’s transfer curve). digiKam is likely applying a more photographer-friendly default rendering, even if its UI appears “neutral.”
So while both may use LibRaw, they are not necessarily doing an identical pipeline after demosaicing. digiKam is designed to give pleasing photographic defaults; LibRaw/dcraw_emu is designed to expose lower-level control and may produce a more literal output unless you add the desired tone/gamma adjustments yourself.
Also, ICC input/output profile settings affect color management, but they do not by themselves guarantee the same tone rendering between applications.
In short: same RAW engine, different processing defaults. The visual mismatch is likely due to digiKam applying gamma/tone mapping that your dcraw_emu command is not reproducing.
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