Re: RFC on proposed patches to mr97310a.c for gspca and v4l

[Thomas Kaiser <v4l@kaiser-linux.li>]

Hello Theodore

kilgota@banach.math.auburn.edu wrote:
> 
> 
> On Wed, 4 Mar 2009, Thomas Kaiser wrote:
> As to the actual contents of the header, as you describe things,
> 
> 0. Do you have any idea how to account for the discrepancy between
> 
>>>  From usb snoop.
>>> FF FF 00 FF 96 64 xx 00 xx xx xx xx xx xx 00 00
> and
>>> In Linux the header looks like this:
>>>
>>> FF FF 00 FF 96 64 xx 00 xx xx xx xx xx xx F0 00
> 
> (I am referring to the 00 00 as opposed to F0 00)? Or could this have 
> happened somehow just because these were not two identical sessions?

Doesn't remember what the differences was. The first is from Windoz 
(usbsnoop) and the second is from Linux.

> 
>>> 1. xx: don't know but value is changing between 0x00 to 0x07
> 
> as I said, this signifies the image format, qua compression algorithm in 
> use, or if 00 then no compression.

On the PAC207, the compression can be controlled with a register called 
"Compression Balance size". So, I guess, depending on the value set in 
the register this value in the header will show what compression level 
is set.

> 
>>> 2. xx: this is the actual pixel clock
> 
> So there is a control setting for this?

Yes, in the PAC207, register 2. (12 MHz divided by the value set).

> 
>>> 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"
> 
> Does anyone have any idea of how actually to use this information/ for 
> example, since a lot of cameras are reporting some kind of similar 
> looking information, does anyone know if there are any kinds of standard 
> scales for these entries? Just what are they supposed to signify, and 
> how exactly is one supposed to use such values, if they have been 
> presented? When I say "a lot of cameras," understand, I mean still 
> cameras as well as webcams, and cameras with a lot of different chipsets 
> in them, too. So this is a question whether there is any standard system 
> for the presentation of such data, and how it might constructively be 
> used in image processing. I have had questions about this kind of thing 
> for a long time, and I do not know where to look for the answers.

For the brightness, I guess, 0 means dark and 0xff completely bright 
(sensor is in saturation)?

Thomas