On Wednesday 04 March 2009 02:41:05 Thomas Kaiser wrote:
> Hello Theodore
>
> kilg...@banach.math.auburn.edu wrote:
> > Also, after the byte indicator for the compression algorithm there are
> > some more bytes, and these almost definitely contain information which
> > could be valuable while doing image processing on the output. If they
> > are already kept and passed out of the module over to libv4lconvert,
> > then it would be very easy to do something with those bytes if it is
> > ever figured out precisely what they mean. But if it is not done now it
> > would have to be done then and would cause even more trouble.
>
> I sent it already in private mail to you. Here is the observation I made
> for the PAC207 SOF some years ago:
>
> From usb snoop.
> FF FF 00 FF 96 64 xx 00 xx xx xx xx xx xx 00 00
> 1. xx: looks like random value
> 2. xx: changed from 0x03 to 0x0b
> 3. xx: changed from 0x06 to 0x49
> 4. xx: changed from 0x07 to 0x55
> 5. xx: static 0x96
> 6. xx: static 0x80
> 7. xx: static 0xa0
>
> And I did play in Linux and could identify some fields :-) .
> In Linux the header looks like this:
>
> FF FF 00 FF 96 64 xx 00 xx xx xx xx xx xx F0 00
> 1. xx: don't know but value is changing between 0x00 to 0x07
> 2. xx: this is the actual pixel clock
> 3. xx: this is changing according light conditions from 0x03 (dark) to
> 0xfc (bright) (center)
> 4. xx: this is changing according light conditions from 0x03 (dark) to
> 0xfc (bright) (edge)
> 5. xx: set value "Digital Gain of Red"
> 6. xx: set value "Digital Gain of Green"
> 7. xx: set value "Digital Gain of Blue"
>
> Thomas
I've been looking through the frame headers sent by the MR97310A (the Aiptek
PenCam VGA+, 08ca:0111). Here are my observations.
FF FF 00 FF 96 6x x0 xx xx xx xx xx
In binary that looks something like this:
11111111 11111111 00000000 11111111
10010110 011001aa a1010000 bbbbbbbb
bbbbbbbb cccccccc ccccdddd dddddddd
All of the values look to be MSbit first. A looks like a 3-bit frame sequence
number that seems to start with 1 and increments for each frame. B, C, and D
might be brightness and contrast; minimum and maximum values for these vary
with the image size.
For 640x480, 320x240, and 160x120:
dark scene (all black):
B: near 0
C: 0x000
D: 0xC60
bright scene (all white):
B: usually 0xC15C
C: 0xC60
D: 0x000
For 352x288 and 176x144:
dark scene (all black):
B: near 0
C: 0x000
D: 0xB5B
bright scene (all white):
B: usually 0xB0FE
C: 0xB53
D: 0x007
B increases with increasing brightness. C increases with more white pixels
and D increases with more black pixels. A gray image has C and D near zero,
while a high-contrast image (half black, half white) has C and D around 0x600
or so. The sum of C and D is not a constant.
I don't know how brightness and contrast are handled in V4L. Hopefully
someone can put this to use.
-Kyle
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