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Black level measurement explanation revised

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This commit is contained in:
Morgan Hardwood
2018-06-03 11:46:31 +02:00
parent 71a0322ec6
commit f10374607e
1 changed files with 9 additions and 11 deletions
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20
rtengine/camconst.json
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@@ -278,12 +278,15 @@ About black levels:
can be derived from masked pixels (typical for Canon cameras) or otherwise be extracted from some tag.
Some formats have built-in subtraction information and are pre-processed by dcraw to end up at a black level of
zero (Phase One's IIQ). For Panasonic raws beginning from dcraw v9.21 dcraw/RT reads base BL from Exif data (tags 0x001c
BlackLevelRed, 0x001d BlackLevelGreen, 0x001e BlackLevelBlue) and we define in "ranges": { "black": the needed offset
of around 15. The (total) BL RT displays is base+offset In all, you typically should not care about the black
level in camconst.json, any information that can be derived from the raw file itself should not be specified in
camconst.json! Sony's ARW2 is one of the few exceptions (with single black level around 512, or 800 for
RX10/100 models), but dcraw generally has good constants for these already.
zero (Phase One's IIQ).
For Panasonic cameras, the black level defined in camconst.json is the black level offset, which comes from
BlackLevel3 + BlackLevel2. RawTherapee then reads the base black levels from Exif data (0x001c BlackLevelRed,
0x001d BlackLevelGreen and 0x001e BlackLevelBlue) and adds them to the offset.
In all, you typically should not care about the black level in camconst.json, any information that can be derived from
the raw file itself should not be specified in camconst.json! Sony's ARW2 is one of the few exceptions (with a single
black level around 512, or 800 for RX10/100 models), but dcraw generally has good constants for these already.
Currently we have chosen not to provide any guide how to measure black levels as we don't think it will be a common task
(it's also more difficult to do than measure white levels). If you experience a black level issue it's more likely due
@@ -1637,11 +1640,6 @@ Camera constants:
"ranges": { "white": 4050 } // safe for worst case detected, nominal is 4093
},
/* Since dcraw_v9.21 Panasonic base BL is read from Exif (tags 0x001c BlackLevelRed15 is BL offset.
dcraw/RT read the base black from Exif and calculates total BL = BLbase+BLoffset, 0x001d BlackLevelGreen, 0x001e BlackLevelBlue
and we define here the needed offset of around 15. The total BL is base+offset
*/
{ // Quality C, proper ISO 100-125-160 samples missing, pixelshift files have no black offset etc. #4574
"make_model": [ "Panasonic DC-G9" ],
"dcraw_matrix": [ 7685, -2375, -634, -3687, 11700, 2249, -748, 1546, 5111 ], // Adobe DNG Converter 10.3 ColorMatrix2