Webcam outdoors = overexposure

[[email protected]]

Anyone seen a diy solution to why webcams will produce whiteonly pictures
outdoors?,


If I put a bit of cardboard in front of the camera and only allow
light in for short moment. Image quality improves.

One idea would be some kind of small tft/lcd screen in front of the camera.
What would allow light in synchronised with the image download. I know there
is at least some welding protection that works this way =)

There is ofcourse videocameras that does this, But I would like some better
resolution. And fps doesn't matter too much.

 

[René]

On 15 Jun 2005 14:55:39 GMT,

Anyone seen a diy solution to why webcams will produce whiteonly pictures
outdoors?,


If I put a bit of cardboard in front of the camera and only allow
light in for short moment. Image quality improves.

One idea would be some kind of small tft/lcd screen in front of the camera.
What would allow light in synchronised with the image download. I know there
is at least some welding protection that works this way =)

There is ofcourse videocameras that does this, But I would like some better
resolution. And fps doesn't matter too much.

I'd guess the webcam is broken.

The ones I tried are not very sensitive to begin with, and seem to
regulate by changing the exposure time. The el-cheapo Logitech I have
here can hardly be overexposed with any daylight source or powerful
lamp. It *can* be underexposed easily however :-(

Note that the various "automatic" settings need to be invoked. Sure
the settings are not "fixed" (exposure time etc)?

 

[[email protected]]

On 15 Jun 2005 14:55:39 GMT,
[email protected] wrote:

I'd guess the webcam is broken.

The ones I tried are not very sensitive to begin with, and seem to
regulate by changing the exposure time. The el-cheapo Logitech I have
here can hardly be overexposed with any daylight source or powerful
lamp. It *can* be underexposed easily however :-(

Note that the various "automatic" settings need to be invoked. Sure
the settings are not "fixed" (exposure time etc)?

I suspect the exposure time is fixed
I wondered if it could be fixed externaly somehow. But maybe it's possible to
fix with sw. I thought webcams in the lowend didn't have exposure control. But
rather assumed room lightning with bulbs all the time.

 

[OBones]

I suspect the exposure time is fixed
I wondered if it could be fixed externaly somehow. But maybe it's possible to
fix with sw. I thought webcams in the lowend didn't have exposure control. But
rather assumed room lightning with bulbs all the time.

Oh but the exposure time is fixed. It's just that it uses more than one
frame to cope for the lack of light.
Hence, if it is very dark the animation is not smooth at all.

 

[RST Engineering \(jw\)]

There's your problem for sure. Everything is overexposed when lightning
gets into the room.

{;-)

Jim

 

[John Popelish]

Anyone seen a diy solution to why webcams will produce whiteonly pictures
outdoors?,


If I put a bit of cardboard in front of the camera and only allow
light in for short moment. Image quality improves.

One idea would be some kind of small tft/lcd screen in front of the camera.
What would allow light in synchronised with the image download. I know there
is at least some welding protection that works this way =)

There is ofcourse videocameras that does this, But I would like some better
resolution. And fps doesn't matter too much.

If the camera has no exposure settings or automatic exposure control,
the easiest solution may be a neutral density filter (sunglasses).

 

[Georg Acher]

If the camera has no exposure settings or automatic exposure control,
the easiest solution may be a neutral density filter (sunglasses).

The problem may have several causes:

- Usually every webcam has exposure control, but it works only electrically and
can't prohibit overexposure of the sensor pixels in extreme light. For a real
exposure control you need an adjustable iris, but that's too expensive...

- Direct sunlight isn't properly shielded by the black mask on the sensor chip
and disturbs the signal processing circuits (shifts bias etc).

- Sunlight has a high IR component which gets through the cheap IR
filter (usually done by coating on one of the lenses) and makes the image
unsharp and dull.

 

[[email protected]]

You want a DIY solution? Get a pair of cheap POLARIZED sunglasses.
Mount one in the normal orientation in front of the camera lens
(maintaining original orientation is necessary to eliminate glare).
Mount (tape or whatever) the second lens over the first, but rotated
enough to reduce the light coming in to an acceptable level. Simple,
cheap cross-polarized variable neutral density filter.

 

[Lyle]

This is a huge effect since the solar spectral intensity of IR, e.g. at 1
micron is nearly 1/3 the maximum (I believe in the green?) and the CCD
sensitivity is close to 1/4 maximum. what you want is IR and UV blocking
filter. I haven't found a cheap one yet. Let us know if you find one.
Lyle

 

[René]

On 15 Jun 2005 15:19:17 GMT,

I suspect the exposure time is fixed
I wondered if it could be fixed externaly somehow. But maybe it's possible to
fix with sw. I thought webcams in the lowend didn't have exposure control. But
rather assumed room lightning with bulbs all the time.

Even the cheapest of the cheap webcams (like my E20 Logitech) has a
"camera settings" posibility, allowing the exposure, brightness,
contrast etc to be set. usually the default settings will do.

I can point the cam overhere directly at a halogen desk lamp, and it
will even show the filament after some adjustment time.