| 8) Model = Canon DIGITAL IXUS 870 IS | - Tag 0x0110 (26 bytes, string[26]) | | 18) DefaultCropOrigin = 10 10 | | - Tag 0xc61f (8 bytes, int32u[2]) | | 19) DefaultCropSize = 3648 2736 | | - Tag 0xc620 (8 bytes, int32u[2]) | | 20) ActiveArea = 8 14 2764 3682 | | - Tag 0xc68d (16 bytes, int32u[4])
X1, X2 sensor - needs to be divisible by 4Y1, Y2 sensor - needs to be divisible by 2
CAM_ACTIVE_AREA_Y1 = 22CAM_ACTIVE_AREA_X1 = 16CAM_ACTIVE_AREA_Y2 = 2760CAM_ACTIVE_AREA_X2 = 3680
#define CAM_ACTIVE_AREA_X1 12 #define CAM_ACTIVE_AREA_Y1 12 #define CAM_ACTIVE_AREA_X2 4440 #define CAM_ACTIVE_AREA_Y2 3334
It's important to realize here that ActiveArea specifies pixels that show the scene and are not fully covered or partially shaded by covering material.
At the risk of being pedantic, I think you are interchanging the use of the terms RAW and DNG?
I believe that what you are describing here is the four pieces of information embedded in the DNG header for the DNG file created around the RAW information?
So I think what you are asking is two things First of all, are the DNG file header active area values optimal? And second, are there variations in the sensor masking that will result in different "optimal" values.
There are at least a couple of forum threads about how those values are determined but it largely comes down to the care and diligence of the person who did the original port (i.e. quite variable) and their guess about which rows & columns in the sensor data were actually completely active.
This also opens up the same question for cameras that support native RAW when looking at the CHDK DNG files for those cameras
QuoteIt's important to realize here that ActiveArea specifies pixels that show the scene and are not fully covered or partially shaded by covering material.My philosophy for CHDK has been to include all pixels that show recognizable image data, even if they aren't at the same level as the rest of the sensor.
1) most people who really use raw will crop their shots anyway
2) Occasionally, salvaging those border pixels will be worthwhile
3) If the active area does not include them, then you can only access them by hacking the DNG header..
4) It's not always clear where the edge of the "good" pixels is.
Some discussion can be found in http://chdk.setepontos.com/index.php?topic=11591.msg113570#msg113570Note that in CHDK 1.3, you adjust the default crop per Phil's suggestion in that thread. The ability to set "full" may negate #3 above.
In general, the active area and default crop are is at the mercy of the person who did the port. Some of them are quite bad, and fixing the ones that are obvious wrong would be a good thing.
Quote from: reyalp on 30 / August / 2014, 23:35:522) Occasionally, salvaging those border pixels will be worthwhileI tried out of curiosity. I found varying exposure levels and it didn't work out well. We are talking about 10px or so out of usually several thousand. Cases where salvaging those border pixels will be worthwhile might exist but they'll be rare I'd reckon.
So only changing it to "Full" which will change the ActiveArea, too would have an influence there.
All DIGIC IV and later cameras currently supported by CHDK with the exception of A1100, A2100, D10, IXUS 95, IXUS 100, IXUS 980, SX10, SX20, SX120 do use it. DIGIC III and DIGIC II cameras generally don't. Those that do should default to ActiveArea those that don't should default to JPEG in terms of crop.
To conclude I could imagine doing the following:- providing three sets of measurementsa) top, left, bottom, right fully masked (black pixels) on sensorb) top, left, bottom, right partially shaded pixels not at the sensor's general exposure levelc) for those where it's relevant X, Y position of upper left JPEG corner on sensora) can be used to define ActiveArea according to reyalp's preference.b) can be used to define it according to mine.Since there already is a crop setting in CHDK we could have both (replacing current ActiveArea setting) where both settings would influence Active Area (as now does Full Sensor) and make DefaultCropOrigin 0,0 and Crop size the full ActiveArea. I'd use Active Area b for the JPEG setting (as a fall back where the RAW converter doesn't support the Crop meta tags)Well, this is probably too long a reply as it is... So let's stop here.
Just a quick note: the "partially shaded border" is much less shaded on images taken with zoom. It exists because vignetting correction is not applied to the border area.
Quote from: koshy on 31 / August / 2014, 16:30:03Quote from: reyalp on 30 / August / 2014, 23:35:522) Occasionally, salvaging those border pixels will be worthwhileI tried out of curiosity. I found varying exposure levels and it didn't work out well. We are talking about 10px or so out of usually several thousand. Cases where salvaging those border pixels will be worthwhile might exist but they'll be rare I'd reckon.Probably true. I wonder if you can reliably recover them with a flat field?
Generally this is interesting. Yet another digital processing step in what's supposed to be "RAW". Do you know of others? I take it that this is on the other side of DIGIC and cannot be influenced by CHDK?
Once again, did I miss something here? The RAW image file is every pixel available from the sensor. The DNG has the same information, but some "meta info" is added to point out which parts of the sensor data are actually likely to be useful. Nothing to do with CHDK here - it's all there. Just pick what part of the sensor data you want to work with in "post processing".
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