Hello Theodore
kilgota@xxxxxxxxxxxxxxxxxxxxxx wrote:
For the brightness, I guess, 0 means dark and 0xff completely bright
(sensor is in saturation)?
That of course is a guess. OTOH it could be on a scale of 0 to 0x80, or
it could be that only the digits 0 through 9 are actually used, and the
basis is then 100, or too many other variations to count. Also what is
considered a "normal" or an "average" value? The trouble with your
suggestion of a scale from 0 to 0xff is that it makes sense, and in a
situation like this one obviously can not assume that.
I don't really understand what you try to tell with this sentence:
"and in a situation like this one obviously can not assume that."
The values changed from 0x03 (dark) to 0xfc (bright), for me does this
mean that the scale goes from 0x00 to 0xff!? Or I am wrong?
What I am suspecting is that these things have some kind of standard
definitions, which are not necessarily done by logic but by convention,
and there is a document out there somewhere which lays it all down. The
document could have been produced by Microsoft, for example, which
doubtless has its own problems reducing chaos to order in the industry,
or by some kind of consortium of camera manufacturers, or something like
that. I really do strongly suspect that the interpretation of all of
this is written down somewhere. But I don't know where to look.
I believe that this documents are exists, but not available for
public:-( Just company confidential.
Anyway most of the Linux webcam drivers were done by re-engineering the
Windoz driver (usbsnoop). That said, all information about the cams is
"a guess".
For the brightness thing, I just was working with a light and studied
what is changing in the header of the frame. At this time I did this, I
was not aware that I could remove the lens of the webcam to be more
sensible to light change and get more precise results.
During the work I did for the PAC7311 Pixart chip I found out that
removing the lens and put light directly to the sensor does help a lot
to figure out how the cam is working.
And with this idea in mind, we could even get further to guess the
compression algo from a cam.
Assuming that the sensor has a Bayer pattern.
- remove lens.
- put white light on the sensor
- use color filter an put each spectrum (RGB) on the sensor
- check the stream and find out what is changing in the stream according
to the different light conditions.
Looks like I get off topic, now ;-)
Something else comes in my mind. Would it good to document all this what
we are talking bout somewhere on a webpage?
Thomas
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