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Depending on the offset of

Depending on the offset of the active zone, camera model (obviously), and firmware - useful Bayer patterns can be different. Answering pattern questions, specific to model, firmware, or active zone, makes sense only if there is a bug in the library, and only with a "thank you!".

From LibRaw docs:

unsigned black;
Black level. Depending on the camera, it may be zero (this means that black has been subtracted at the unpacking stage or by the camera itself), calculated at the unpacking stage, read from the RAW file, or hardcoded.

my comment: if only one black level value is found / hardcoded / calculated, it is in this field. Before using it, you may want to check the content of cblack.

More from docs:
unsigned cblack[4102];
Per-channel black level correction. First 4 values are per-channel correction, next two are black level pattern block size, than cblack[4]*cblack[5] correction values (for indexes [6....6+cblack[4]*cblack[5]).

my comment: if 4 (per channel) black level values are found / calculated from sources other than Adobe EXIF tag (with one exception that is irrelevant for the matter at hand), for the camera you are interested in they are read into cblack[0 .. 3] in 0 1 3 2 index order (see code, permutations
FORC4 cblack[c ^ c >> 1] = get2();
do that. That's the way Mr. Coffin did it in dcraw, and we preserved it in LibRaw for compatibility.)

if cblack[0] is 0, and / or cblack[4 .. 5] are present (DNG), you can use cblack [6 .. ...]. You can follow the code under "case 0xc61a" to see the order cblack is populated in this case. For a regular DNG, the cycle in essence is
FORC(cblack[4] * cblack[5]) cblack[6+c] = getreal(type);
meaning, the order coming from Adobe EXIF tag is preserved. Again, preserved from dcraw for compatibility.

Iliah Borg