Canon 350D WB RGGB Levels

[tlahey]

Hello - I am new to this forum and just started using ExifTool.  I do astrophotography with a Canon Digital Rebel XT (350D).

When I extracted the EXIF data for one of my .CR2 images, I am puzzled by what shows for Color Balance.  Perhaps I just don't understand the exact meanings of the tags, but I could not find any better explanation under Tag Names Explained, or in the Canon tag info.

Parts of the data appear below.

What puzzles me is the interpretation of the WB RGGB Levels.

The image was taken with the camera set to WB = Daylight, and this is shown correctly next to the tag White Balance.

Farther down, the data shows WB RGGB Levels As Shot: 2328 1018 1020 1490

However, under that it shows WB RGG B Levels Daylight: 2328 1022 1024 1490

What I find confusing is that the "As Shot" levels don't match the "Daylight" levels.  I would have expected that the they would be the same.

Is there some explanation for this?

I should also point out that the camera was set to Parameters=1, which results in the Contrast: +1, Saturation: +1, Sharpness: +1 tags (I think).


Thanks for any insight you can offer.

And thanks Phil for creating such an enormously powerful and flexible tool!  As a programmer, I am impressed.

Regards
Tim Lahey
Owen Sound, Ontario

Code Select Expand

ExifTool Version Number         : 8.46
File Name                       : IMG_5563.CR2

Contrast                        : +1
Saturation                      : +1
Sharpness                       : +1

White Balance                   : Daylight

Sharpness Frequency             : n/a
Sensor Red Level                : 0
Sensor Blue Level               : 0
White Balance Red               : 0
White Balance Blue              : 0
Color Temperature               : -1
Picture Style                   : None
Digital Gain                    : 0
WB Shift AB                     : 0
WB Shift GM                     : 0
Measured RGGB                   : 471 1024 1024 444
VRD Offset                      : 0
Sensor Width                    : 3516
Sensor Height                   : 2328
Sensor Left Border              : 52
Sensor Top Border               : 19
Sensor Right Border             : 3507
Sensor Bottom Border            : 2322
Black Mask Left Border          : 0
Black Mask Top Border           : 0
Black Mask Right Border         : 0
Black Mask Bottom Border        : 0
WB RGGB Levels As Shot          : 2328 1018 1020 1490
Color Temp As Shot              : 5200
WB RGGB Levels Auto             : 1919 1022 1024 1712
Color Temp Auto                 : 4236
WB RGGB Levels Daylight         : 2328 1022 1024 1490
Color Temp Daylight             : 5200
WB RGGB Levels Shade            : 2779 1022 1024 1228
Color Temp Shade                : 7000
WB RGGB Levels Cloudy           : 2555 1022 1024 1340
Color Temp Cloudy               : 6000
WB RGGB Levels Tungsten         : 1520 1022 1024 2381
Color Temp Tungsten             : 3200
WB RGGB Levels Fluorescent      : 1940 1022 1024 2022
Color Temp Fluorescent          : 3901
WB RGGB Levels Flash            : 2659 1022 1024 1290
Color Temp Flash                : 6451
WB RGGB Levels Custom 1         : 2328 1022 1024 1490
Color Temp Custom 1             : 5200
WB RGGB Levels Custom 2         : 1103 1022 1024 3294
Color Temp Custom 2             : 2500
Color Tone                      : Normal

WB RGGB Levels                  : 2328 1018 1020 1490
Blue Balance                    : 1.462218
Circle Of Confusion             : 0.019 mm
Field Of View                   : 26.0 deg
Focal Length                    : 50.0 mm (35 mm equivalent: 78.1 mm)
Hyperfocal Distance             : 65.00 m
Lens                            : 50.0 mm (35 mm equivalent: 78.1 mm)
Light Value                     : -8.2
Red Balance                     : 2.284593

Edit: Fixed formatting so I could read the post - PH

[Phil Harvey]

Hi Tim,

I really don't know the details of what goes on inside the 350D firmware, but your "As Shot" levels are very close to what I assume are the preset Daylight levels stored in the camera.  It could be that the camera just tweaks these levels a bit for each image.  I know for sure that my Pentax K-5 does this -- it even has a menu setting to specify how much freedom it is allowed when tweaking WB in Tungsten mode.

- Phil