Setting up the exposure time of a webcam

Setting up the exposure time of a webcam

[Nicolau Werneck]

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Hello. I have this very cheap webcam that I sent a patch to support on
gspca the other day. The specific driver is the t613.

I changed the lens of this camera, and now my images are all too
bright, what I believe is due to the much larger aperture of this new
lens. So I would like to try setting up a smaller exposure time on the
camera (I would like to do that for other reasons too).

The problem is there's no "exposure" option to be set when I call
programs such as v4lctl. Does that mean there is definitely no way for
me to control the exposure time? The hardware itself was not designed
to allow me do that? Or is there still a chance I can create some C
program that might do it, for example?

It looks like the camera has some kind of automatic exposure control. If
I cover the lens, and then uncover it quickly, the image is all white
at first, and then it gradually becomes darker. Should that give me
some hope of being able to control the exposure, or is it common for
cheaper cameras to have just an automatic exposure control that cannot
be overrun?

Thanks,
  ++nicolau





-- 
Nicolau Werneck <nwerneck@gmail.com>          1AAB 4050 1999 BDFF 4862
http://www.lti.pcs.usp.br/~nwerneck           4A33 D2B5 648B 4789 0327
Linux user #460716


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Re: Setting up the exposure time of a webcam

[Nicolau Werneck]

Thanks for the reply, I'll look out for those possible correction
commands... But the adjustment when I cover the lens already happens
in the Linux driver, so I guess it's just something internal, right?

I went back to the original driver to see if I could make the camera
usable again, and I succeeded by turning off the automatic white
balance, and changing the values of the balance by hand. There are
three values for R G and B that can be set from 0 to 127. Can gspca
support something like that? v4lctl doesn't offer anything like that
out of the box, and I couldn't find possible functions in the
code. Does that array in the setwhitebalance function (t613.c) set
these values that the win driver offers the user to set?

thanks,
 
   ++nicolau


On Tue, Jan 26, 2010 at 12:18:01PM -0600, Theodore Kilgore wrote:
>
>
> On Tue, 26 Jan 2010, Nicolau Werneck wrote:
>
>> Hello. I have this very cheap webcam that I sent a patch to support on
>> gspca the other day. The specific driver is the t613.
>>
>> I changed the lens of this camera, and now my images are all too
>> bright, what I believe is due to the much larger aperture of this new
>> lens. So I would like to try setting up a smaller exposure time on the
>> camera (I would like to do that for other reasons too).
>>
>> The problem is there's no "exposure" option to be set when I call
>> programs such as v4lctl. Does that mean there is definitely no way for
>> me to control the exposure time? The hardware itself was not designed
>> to allow me do that? Or is there still a chance I can create some C
>> program that might do it, for example?
>>
>> It looks like the camera has some kind of automatic exposure control. If
>> I cover the lens, and then uncover it quickly, the image is all white
>> at first, and then it gradually becomes darker. Should that give me
>> some hope of being able to control the exposure, or is it common for
>> cheaper cameras to have just an automatic exposure control that cannot
>> be overrun?
>
> Nicolau,
>
> Having had some experience with cheap cameras, I would say that they come 
> with all kinds of variations. Thus, this particular camera (with which I  
> am _not_ experienced) could either have a built-in automatic exposure  
> control, or it could require monitoring from software with periodic  
> correction of various settings. It just depends.
>
> Thus, one thing to do is to look carefully at some usbsnoop logs and try  
> to see if there are occasional correction sequences in between big hunks  
> of data. If there are, then the next thing is to figure out what those  
> correction sequences are doing. Then build those correction sequences 
> into the driver. An example of this kind of thing going on can be seen  
> in lots of the camera drivers in gspca, but not in all of them.
>
> Second thing, try to look for sensor setup commands which give initial  
> settings. If there are such, then one or more of them might control  
> exposure settings.
>
> Third, if there are no occurences of either of the previous items at all, 
> then either the camera does not self-adjust and can not be adjusted (i. 
> e. really, really cheap), or the adjustment mechanism is completely 
> built-in. In that case, I would say that you are probably up a tree about 
> getting the exposure reset.
>
> Hope this helps you.
>
> Theodore Kilgore

-- 
Nicolau Werneck <nwerneck@gmail.com>          1AAB 4050 1999 BDFF 4862
http://www.lti.pcs.usp.br/~nwerneck           4A33 D2B5 648B 4789 0327
Linux user #460716

Re: Setting up the exposure time of a webcam

[Theodore Kilgore]

On Tue, 26 Jan 2010, Nicolau Werneck wrote:

> Hello. I have this very cheap webcam that I sent a patch to support on
> gspca the other day. The specific driver is the t613.
>
> I changed the lens of this camera, and now my images are all too
> bright, what I believe is due to the much larger aperture of this new
> lens. So I would like to try setting up a smaller exposure time on the
> camera (I would like to do that for other reasons too).
>
> The problem is there's no "exposure" option to be set when I call
> programs such as v4lctl. Does that mean there is definitely no way for
> me to control the exposure time? The hardware itself was not designed
> to allow me do that? Or is there still a chance I can create some C
> program that might do it, for example?
>
> It looks like the camera has some kind of automatic exposure control. If
> I cover the lens, and then uncover it quickly, the image is all white
> at first, and then it gradually becomes darker. Should that give me
> some hope of being able to control the exposure, or is it common for
> cheaper cameras to have just an automatic exposure control that cannot
> be overrun?

Nicolau,

Having had some experience with cheap cameras, I would say that they come 
with all kinds of variations. Thus, this particular camera (with which I 
am _not_ experienced) could either have a built-in automatic exposure 
control, or it could require monitoring from software with periodic 
correction of various settings. It just depends.

Thus, one thing to do is to look carefully at some usbsnoop logs and try 
to see if there are occasional correction sequences in between big hunks 
of data. If there are, then the next thing is to figure out what those 
correction sequences are doing. Then build those correction sequences into 
the driver. An example of this kind of thing going on can be seen 
in lots of the camera drivers in gspca, but not in all of them.

Second thing, try to look for sensor setup commands which give initial 
settings. If there are such, then one or more of them might control 
exposure settings.

Third, if there are no occurences of either of the previous items at all, 
then either the camera does not self-adjust and can not be adjusted (i. e. 
really, really cheap), or the adjustment mechanism is completely built-in. 
In that case, I would say that you are probably up a tree about getting 
the exposure reset.

Hope this helps you.

Theodore Kilgore

Re: Setting up the exposure time of a webcam

[Jean-Francois Moine]

On Tue, 26 Jan 2010 15:00:53 -0200
Nicolau Werneck <nwerneck@gmail.com> wrote:

> Hello. I have this very cheap webcam that I sent a patch to support on
> gspca the other day. The specific driver is the t613.
> 
> I changed the lens of this camera, and now my images are all too
> bright, what I believe is due to the much larger aperture of this new
> lens. So I would like to try setting up a smaller exposure time on the
> camera (I would like to do that for other reasons too).
> 
> The problem is there's no "exposure" option to be set when I call
> programs such as v4lctl. Does that mean there is definitely no way for
> me to control the exposure time? The hardware itself was not designed
> to allow me do that? Or is there still a chance I can create some C
> program that might do it, for example?
	[snip]

Hello Nicolau,

There are brightness, contrast, colors, autogain and some other video
controls for the t613 webcams. You must use a v4l2 compliant program to
change them, as vlc or v4l2ucp (but not cheese).

Regards.

-- 
Ken ar c'hentañ	|	      ** Breizh ha Linux atav! **
Jef		|		http://moinejf.free.fr/

Re: Setting up the exposure time of a webcam

[leandro Costantino]

HI Nicolau....
remember to send a SOB if the patch is working, and any change let me
know so i can test with others t613 users.
Best Regards

On Tue, Jan 26, 2010 at 3:37 PM, Jean-Francois Moine <moinejf@free.fr> wrote:
> On Tue, 26 Jan 2010 15:00:53 -0200
> Nicolau Werneck <nwerneck@gmail.com> wrote:
>
>> Hello. I have this very cheap webcam that I sent a patch to support on
>> gspca the other day. The specific driver is the t613.
>>
>> I changed the lens of this camera, and now my images are all too
>> bright, what I believe is due to the much larger aperture of this new
>> lens. So I would like to try setting up a smaller exposure time on the
>> camera (I would like to do that for other reasons too).
>>
>> The problem is there's no "exposure" option to be set when I call
>> programs such as v4lctl. Does that mean there is definitely no way for
>> me to control the exposure time? The hardware itself was not designed
>> to allow me do that? Or is there still a chance I can create some C
>> program that might do it, for example?
>        [snip]
>
> Hello Nicolau,
>
> There are brightness, contrast, colors, autogain and some other video
> controls for the t613 webcams. You must use a v4l2 compliant program to
> change them, as vlc or v4l2ucp (but not cheese).
>
> Regards.
>
> --
> Ken ar c'hentañ |             ** Breizh ha Linux atav! **
> Jef             |               http://moinejf.free.fr/
> --
> To unsubscribe from this list: send the line "unsubscribe linux-media" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>

Setting up white balance on a t613 camera

[Nicolau Werneck]

Hello again, people. I believe I have found in my log the commands
that are setting up that white balance parameters. I am pasting an
excerpt of the log at the end. (I changed the subject now that is
seems this is actually the way I should follow)

It looks to me that in that SetupPacket vector the "88" encodes what
channel to set. 87 for red, 88 for blue and 89 for green. The
following value is the level, which is default to 0x20. 

The question now is how do I offer to set up that parameter in the
driver? What function can I use to transmits a vector that way, so I
can make a hacky test?

In other words: would it be possible or me to just cut and paste some
code in the driver to implement that? Or will I be finally forced to
actually learn what I am doing? :)

regards,

   ++nicolau


(...)
[61857 ms]  <<<  URB 393 coming back  <<< 
-- URB_FUNCTION_CONTROL_TRANSFER:
  PipeHandle           = 89fecb10
  TransferFlags        = 0000000a (USBD_TRANSFER_DIRECTION_OUT,
  USBD_SHORT_TRANSFER_OK)
  TransferBufferLength = 00000000
  TransferBuffer       = 00000000
  TransferBufferMDL    = 00000000
  UrbLink              = 00000000
  SetupPacket          =
    00000000: 40 00 00 00 88 1c 00 00
[61910 ms] UsbSnoop - DispatchAny(bac00610) :
IRP_MJ_INTERNAL_DEVICE_CONTROL
[61910 ms] UsbSnoop - MyDispatchInternalIOCTL(bac01e80) :
fdo=89cf58b0, Irp=89473e48, IRQL=0
[61910 ms]  >>>  URB 394 going down  >>> 
-- URB_FUNCTION_VENDOR_DEVICE:
  TransferFlags          = 00000000 (USBD_TRANSFER_DIRECTION_OUT,
  ~USBD_SHORT_TRANSFER_OK)
  TransferBufferLength = 00000000
  TransferBuffer       = 00000000
  TransferBufferMDL    = 00000000

    no data supplied
  UrbLink                 = 00000000
  RequestTypeReservedBits = 00000000
  Request                 = 00000000
  Value                   = 00000000
  Index                   = 00001e88
[61913 ms] UsbSnoop - MyInternalIOCTLCompletion(bac01db0) :
  fido=00000000, Irp=89473e48, Context=898d8fe8, IRQL=2
[61913 ms]  <<<  URB 394 coming back  <<< 
-- URB_FUNCTION_CONTROL_TRANSFER:
  PipeHandle           = 89fecb10
  TransferFlags        = 0000000a (USBD_TRANSFER_DIRECTION_OUT,
  USBD_SHORT_TRANSFER_OK)
  TransferBufferLength = 00000000
  TransferBuffer       = 00000000
  TransferBufferMDL    = 00000000
  UrbLink              = 00000000
  SetupPacket          =
    00000000: 40 00 00 00 88 1e 00 00
[61950 ms] UsbSnoop - DispatchAny(bac00610) :
  IRP_MJ_INTERNAL_DEVICE_CONTROL
[61950 ms] UsbSnoop - MyDispatchInternalIOCTL(bac01e80) :
  fdo=89cf58b0, Irp=89f97008, IRQL=0
[61950 ms]  >>>  URB 395 going down  >>> 
-- URB_FUNCTION_VENDOR_DEVICE:
  TransferFlags          = 00000000 (USBD_TRANSFER_DIRECTION_OUT,
  ~USBD_SHORT_TRANSFER_OK)
  TransferBufferLength = 00000000
  TransferBuffer       = 00000000
  TransferBufferMDL    = 00000000

    no data supplied
  UrbLink                 = 00000000
  RequestTypeReservedBits = 00000000
  Request                 = 00000000
  Value                   = 00000000
  Index                   = 00002088
(...)




On Tue, Jan 26, 2010 at 07:37:26PM +0100, Jean-Francois Moine wrote:
> On Tue, 26 Jan 2010 15:00:53 -0200
> Nicolau Werneck <nwerneck@gmail.com> wrote:
> 
> > Hello. I have this very cheap webcam that I sent a patch to support on
> > gspca the other day. The specific driver is the t613.
> > 
> > I changed the lens of this camera, and now my images are all too
> > bright, what I believe is due to the much larger aperture of this new
> > lens. So I would like to try setting up a smaller exposure time on the
> > camera (I would like to do that for other reasons too).
> > 
> > The problem is there's no "exposure" option to be set when I call
> > programs such as v4lctl. Does that mean there is definitely no way for
> > me to control the exposure time? The hardware itself was not designed
> > to allow me do that? Or is there still a chance I can create some C
> > program that might do it, for example?
> 	[snip]
> 
> Hello Nicolau,
> 
> There are brightness, contrast, colors, autogain and some other video
> controls for the t613 webcams. You must use a v4l2 compliant program to
> change them, as vlc or v4l2ucp (but not cheese).
> 
> Regards.
> 
> -- 
> Ken ar c'hentañ	|	      ** Breizh ha Linux atav! **
> Jef		|		http://moinejf.free.fr/
> --
> To unsubscribe from this list: send the line "unsubscribe linux-media" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

-- 
Nicolau Werneck <nwerneck@gmail.com>          1AAB 4050 1999 BDFF 4862
http://www.lti.pcs.usp.br/~nwerneck           4A33 D2B5 648B 4789 0327
Linux user #460716

Re: Setting up white balance on a t613 camera

[Nicolau Werneck]

Answering my own question, and also a question in the t613 source
code...

Yes, the need for the "reg_w(gspca_dev, 0x2087);", 0x2088 and 0x2089
commands are definitely tied to the white balance. These three set up
the default values I found out. And (X << 8 + 87) sets up the red
channel parameter in general, and 88 is for green and 89 for blue.

That means I can already just play with them and see what happens. My
personal problem is that I bought this new lens, and the image is way
too bright, and changing that seems to help. But I would like to offer
these as parameters the user can set using v4l2 programs. I can try
making that big change myself, but help from a more experienced
developer would be certainly much appreciated!...

   ++nicolau




On Wed, Jan 27, 2010 at 02:37:09PM -0200, Nicolau Werneck wrote:
> Hello again, people. I believe I have found in my log the commands
> that are setting up that white balance parameters. I am pasting an
> excerpt of the log at the end. (I changed the subject now that is
> seems this is actually the way I should follow)
> 
> It looks to me that in that SetupPacket vector the "88" encodes what
> channel to set. 87 for red, 88 for blue and 89 for green. The
> following value is the level, which is default to 0x20. 
> 
> The question now is how do I offer to set up that parameter in the
> driver? What function can I use to transmits a vector that way, so I
> can make a hacky test?
> 
> In other words: would it be possible or me to just cut and paste some
> code in the driver to implement that? Or will I be finally forced to
> actually learn what I am doing? :)
> 
> regards,
> 
>    ++nicolau

-- 
Nicolau Werneck <nwerneck@gmail.com>          1AAB 4050 1999 BDFF 4862
http://www.lti.pcs.usp.br/~nwerneck           4A33 D2B5 648B 4789 0327
Linux user #460716

Re: Setting up white balance on a t613 camera

[Jean-Francois Moine]

On Wed, 27 Jan 2010 15:17:53 -0200
Nicolau Werneck <nwerneck@gmail.com> wrote:

> Answering my own question, and also a question in the t613 source
> code...
> 
> Yes, the need for the "reg_w(gspca_dev, 0x2087);", 0x2088 and 0x2089
> commands are definitely tied to the white balance. These three set up
> the default values I found out. And (X << 8 + 87) sets up the red
> channel parameter in general, and 88 is for green and 89 for blue.
> 
> That means I can already just play with them and see what happens. My
> personal problem is that I bought this new lens, and the image is way
> too bright, and changing that seems to help. But I would like to offer
> these as parameters the user can set using v4l2 programs. I can try
> making that big change myself, but help from a more experienced
> developer would be certainly much appreciated!...

Hello Nicolau,

The white balance is set in setwhitebalance(). Four registers are
changed: 87, 88, 89 and 80.

Looking at the traces I have, these 4 registers are loaded together only
one time in an exchange at startup time. Then, the white balance
control adjusts only blue and red values while reloading the same value
for the green register (that's what is done for other webcams), and the
register 80 is not touched. In the different traces, the register 80
may be initialized to various values as 3c, ac or 38 and it is not
touched later. I do not know what it is used for.

I may also notice that the green value in the white balance exchanges
may have an other value than the default 20. I do not know which is the
associated control in the ms-win driver. If it is exposure, you are
done. So, one trivial patch is:

- add the exposure control with min: 0x10, max: 0x40, def: 0x20.

- modify the whitebalance control with min: -16, max +16, def:0.

- there is no function setexposure() because the exposure is the value
  of green register. Both controls exposure and white balance call the
  function setwhitebalance().

- in the function setwhitebalance(), set the green value to the
  exposure, the red value to (exposure + whitebalance) and blue value
  to (exposure - whitebalance) and load only the registers 87, 88 and
  89.

An other way could be to implement the blue and red balances in the
same scheme, and to remove the whitebalance.

Cheers.

-- 
Ken ar c'hentañ	|	      ** Breizh ha Linux atav! **
Jef		|		http://moinejf.free.fr/

Re: Setting up white balance on a t613 camera

[leandro Costantino]

Yes, as wrote in the code, it tied to whitebalance.
Also note that , as Jean wrote, there's are many different values
wrote on some registers, that we don't really know what they are used
for, so,
i would like to go for the most non intrusive option, since, some of
this whitebalance regs, have been adjusted time to time to meet other
t613 users requirment's, and maybe implementing the r/b balance would
be the way to go.

If you want, i can write it so you can test it, or if you prefeer you
can take a look at
http://linuxtv.org/hg/~jfrancois/gspca/file/21f2eeb240db/linux/drivers/media/video/gspca/sonixj.c
at how its done  as an example.

Since i only had this webcam for 1 week, i always relay on the some
group of users that are willing to test each change always.

Best Regadrs.
Costantino Leandro

On Wed, Jan 27, 2010 at 3:37 PM, Jean-Francois Moine <moinejf@free.fr> wrote:
> On Wed, 27 Jan 2010 15:17:53 -0200
> Nicolau Werneck <nwerneck@gmail.com> wrote:
>
>> Answering my own question, and also a question in the t613 source
>> code...
>>
>> Yes, the need for the "reg_w(gspca_dev, 0x2087);", 0x2088 and 0x2089
>> commands are definitely tied to the white balance. These three set up
>> the default values I found out. And (X << 8 + 87) sets up the red
>> channel parameter in general, and 88 is for green and 89 for blue.
>>
>> That means I can already just play with them and see what happens. My
>> personal problem is that I bought this new lens, and the image is way
>> too bright, and changing that seems to help. But I would like to offer
>> these as parameters the user can set using v4l2 programs. I can try
>> making that big change myself, but help from a more experienced
>> developer would be certainly much appreciated!...
>
> Hello Nicolau,
>
> The white balance is set in setwhitebalance(). Four registers are
> changed: 87, 88, 89 and 80.
>
> Looking at the traces I have, these 4 registers are loaded together only
> one time in an exchange at startup time. Then, the white balance
> control adjusts only blue and red values while reloading the same value
> for the green register (that's what is done for other webcams), and the
> register 80 is not touched. In the different traces, the register 80
> may be initialized to various values as 3c, ac or 38 and it is not
> touched later. I do not know what it is used for.
>
> I may also notice that the green value in the white balance exchanges
> may have an other value than the default 20. I do not know which is the
> associated control in the ms-win driver. If it is exposure, you are
> done. So, one trivial patch is:
>
> - add the exposure control with min: 0x10, max: 0x40, def: 0x20.
>
> - modify the whitebalance control with min: -16, max +16, def:0.
>
> - there is no function setexposure() because the exposure is the value
>  of green register. Both controls exposure and white balance call the
>  function setwhitebalance().
>
> - in the function setwhitebalance(), set the green value to the
>  exposure, the red value to (exposure + whitebalance) and blue value
>  to (exposure - whitebalance) and load only the registers 87, 88 and
>  89.
>
> An other way could be to implement the blue and red balances in the
> same scheme, and to remove the whitebalance.
>
> Cheers.
>
> --
> Ken ar c'hentañ |             ** Breizh ha Linux atav! **
> Jef             |               http://moinejf.free.fr/
> --
> To unsubscribe from this list: send the line "unsubscribe linux-media" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>

Re: Setting up white balance on a t613 camera

[Hans de Goede]

Hi,

On 01/27/2010 07:37 PM, Jean-Francois Moine wrote:
> On Wed, 27 Jan 2010 15:17:53 -0200
> Nicolau Werneck<nwerneck@gmail.com>  wrote:
>
>> Answering my own question, and also a question in the t613 source
>> code...
>>
>> Yes, the need for the "reg_w(gspca_dev, 0x2087);", 0x2088 and 0x2089
>> commands are definitely tied to the white balance. These three set up
>> the default values I found out. And (X<<  8 + 87) sets up the red
>> channel parameter in general, and 88 is for green and 89 for blue.
>>
>> That means I can already just play with them and see what happens. My
>> personal problem is that I bought this new lens, and the image is way
>> too bright, and changing that seems to help. But I would like to offer
>> these as parameters the user can set using v4l2 programs. I can try
>> making that big change myself, but help from a more experienced
>> developer would be certainly much appreciated!...
>
> Hello Nicolau,
>
> The white balance is set in setwhitebalance(). Four registers are
> changed: 87, 88, 89 and 80.
>

Hi,

About whitebalancing, currently libv4l does whitebalancing completely
in software for camera's which cannot do it automatically in hardware.

That is libv4l calculates and applies 3 software gains to get
the average green red and blue values the same.

In the future it might be an idea to start supporting hardware per
color gains for this, but there are a number of issues with that:

1) The controls used for this then need to be standardized.
2) As we don't know the exact dB scale of the hardware gains we
need some sort of approximation algorithm, like with autogain /
exposure. Leading to potential overshoot, oscilating etc.

Esp 2. makes me wonder if we want to use the hardware color gains
(when the hardware cannot autoadjust them) at all. Calculating
a software gain so that the averages become equal is trivial, and
does not need any settling time etc.

Note that in case of whitebalance the color correction gain can
easily be done in software (as it is in the range of circa 0.7 - 1.3)
unlike things like exposure and the main gain which we really
must set correctly at the hardware level for a usable picture.

To give libv4l's software whitebalance a try do:

export LIBV4LCONTROL_FLAGS=8

And then run a webcam viewing app from the same commandline

You can also run a control panel like v4l2ucp like this:
export LIBV4LCONTROL_FLAGS=8
LD_PRELOAD=/usr/lib/libv4l/v4l2convert.so v4l2ucp

To get a whitebalance control with which you can toggle
the whitebalance on/off while streaming so that you can
see the effect it has on the picture.

Regards,

Hans