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Bug #9362

The displayed kelvin white balance temperature is very off for D7100 NEFs

Added by Chris Siebenmann about 7 years ago. Updated over 5 years ago.

Status:
Fixed
Priority:
Low
Category:
Darkroom
Target version:
-
Start date:
04/12/2013
Due date:
% Done:

100%

Estimated time:
Affected Version:
git development version
System:
Fedora/RHEL
bitness:
64-bit
hardware architecture:
amd64/x86

Description

Current git versions of darktable will display the white balance temperature in kelvins. This displayed value is quite off for my D7100 NEFs (eg darktable displays photo set to 5000K as 8364K); I assume that this is because the D7100 RGB multipliers use a different mapping than darktable is expecting.

In the hope that it will help you correct this, I've made a series of NEFS at various absolute kelvin settings (with no WB fine tuning) and run them through wb_extract.pl. The resulting output is:

{ "NIKON", "D7100", "2500K", 0,               { 1.214844, 1, 3.382813, 0 } },
  { "NIKON", "D7100", "3450K", 0,               { 1.652344, 1, 2.246094, 0 } },
  { "NIKON", "D7100", "4000K", 0,               { 1.886719, 1, 1.914063, 0 } },
  { "NIKON", "D7100", "5000K", 0,               { 2.332031, 1, 1.652344, 0 } },
  { "NIKON", "D7100", "6250K", 0,               { 2.703125, 1, 1.414063, 0 } },
  { "NIKON", "D7100", "7140K", 0,               { 2.941406, 1, 1.335938, 0 } },
  { "NIKON", "D7100", "8330K", 0,               { 3.230469, 1, 1.320313, 0 } },
  { "NIKON", "D7100", "9090K", 0,               { 3.394531, 1, 1.265625, 0 } },
  { "NIKON", "D7100", "10000K", 0,              { 3.570313, 1, 1, 0 } },

I'd be happy to generate values for other kelvin settings if you'd like them.


Related issues

Related to darktable - Feature #9012: White balance module: temperature sliders do not correspond to anythingFixed10/18/2012

Has duplicate darktable - Bug #10449: Incorrect Kelvin Temperature WB is displayed for Canon 6DClosed: invalid05/09/2015

Associated revisions

Revision 4f4007a6 (diff)
Added by Roman Lebedev over 5 years ago

Temperature iop: implement proper Kelvin temperature. Refs #9362

History

#1 Updated by Pascal de Bruijn over 6 years ago

  • % Done changed from 0 to 100
  • Assignee set to Pascal de Bruijn
  • Status changed from New to Fixed
  • Category set to Darkroom

Again, sorry for the late response.

This issue was indeed a regression, causing way to big discrepancies. But the issue was fixed a while ago in git master, and the fix made it into our latest stable release as well if I'm not mistaken.

Current versions of Darktable (for example 1.2.3) or git master, will report 5200K for it's own 5000K preset, which is good enough.

The process which is used to convert RGB multipliers to kelvin is rather arbitrary (there isn't a single "right" way to do it as far as I'm aware).

#2 Updated by Roman Lebedev over 5 years ago

  • bitness set to 64-bit
As far i can tell, the algo i have recently implemented,
  1. is much more mathematically/colorimetrically correct
  2. produces "more correct values", as in they are rather close to what they "should be" (based on names of those presets of yours and my test shots)
  3. based on my observations
    • When Temperature is < ~6500K, the maximal difference between "expected" and displayed T is within [50K .. 100K]
    • When Temperature is > ~6500K, the maximal difference between "expected" and displayed T is [100K .. 4000K+)

#3 Updated by Roman Lebedev over 5 years ago

  • Related to Feature #9012: White balance module: temperature sliders do not correspond to anything added

#4 Updated by Roman Lebedev about 5 years ago

  • Has duplicate Bug #10449: Incorrect Kelvin Temperature WB is displayed for Canon 6D added

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