My Microdia (SN9C201) webcam succumbs to glare in Linux

My Microdia (SN9C201) webcam succumbs to glare in Linux

[Xavion]

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Hi Guys

As you can probably gather from the attached screenshots, I'm
attempting to use my SN9C201 webcam for home security.  The problem is
that it succumbs to external glare during the middle hours of sunny
days when used in Linux.

The same problem doesn't occur in Windows, probably since the software
automatically adjusts to the current lighting conditions.  These
screenshots were taken only five minutes apart and the sunlight
intensity didn't change much in-between.

No amount of adjusting the webcam's settings (via V4L2-UCP) seemed to
make any significant difference.  For this reason, I'm guessing that
there's at least one other adjustable setting that the GSPCA driver
isn't tapping into yet.

If I'm going to be using this webcam for home security, it will need
to overcome the glare obstacle during these hours.  Otherwise, it
won't take clear snapshots of a potential burglar's face as he looks
in through the windows before entering my unit.

Is there any way that you can modify the GSPCA software to overcome
this glare, as is done in Windows?  If this would require too much
coding at your end, let me know which other webcam I should buy to
overcome this problem in Linux.

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Re: My Microdia (SN9C201) webcam succumbs to glare in Linux

[Jean-Francois Moine]

On Fri, 16 Mar 2012 08:53:51 +1100
Xavion <xavion.0@gmail.com> wrote:

> As you can probably gather from the attached screenshots, I'm
> attempting to use my SN9C201 webcam for home security.  The problem is
> that it succumbs to external glare during the middle hours of sunny
> days when used in Linux.
> 
> The same problem doesn't occur in Windows, probably since the software
> automatically adjusts to the current lighting conditions.  These
> screenshots were taken only five minutes apart and the sunlight
> intensity didn't change much in-between.
> 
> No amount of adjusting the webcam's settings (via V4L2-UCP) seemed to
> make any significant difference.  For this reason, I'm guessing that
> there's at least one other adjustable setting that the GSPCA driver
> isn't tapping into yet.
	[snip]

Hi Xavion,

It seems that the exposure is not set correctly. May you try the patch
below? (to be applied to the gspca test version 2.15.7 - the exposure
may be too low at init time, set it to 800)

--- build/sn9c20x.c~
+++ build/sn9c20x.c
@@ -1650,10 +1650,9 @@
 	case SENSOR_OV7670:
 	case SENSOR_OV9655:
 	case SENSOR_OV9650:
-		exp[0] |= (3 << 4);
-		exp[2] = 0x2d;
-		exp[3] = expo;
-		exp[4] = expo >> 8;
+		exp[0] |= (2 << 4);
+		exp[2] = 0x10;			/* AECH */
+		exp[3] = expo * 255 / 0x1780;
 		break;
 	case SENSOR_MT9M001:
 	case SENSOR_MT9V112:

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

Re: My Microdia (SN9C201) webcam succumbs to glare in Linux

[Xavion]

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Hi Jean-Francois

I applied the patch you supplied, but the result wasn't as expected.
The video now cycles between the attached image and total blackness
every couple of seconds (i.e. bright, black, bright, black, ...).  I
should note that my curtains were actually closed and that I had
auto-exposure enabled in V4L2-UCP.

The image remained the same when I manually set the exposure to 800,
but at least it wasn't going black every couple of seconds anymore.
Of course, the problem disappeared when I reverted to the original
GSPCA v2.15.7 code.  Let me know if you want me to email you any of
the relevant debugging output.

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