BeeJ said:
I need a USB webcam for Win XP or later that must have
1) highest NATIVE resolution (at least 5M Pixels native)
2) auto-focus.
3) best color image (no stinky native images please)
Unfortunately some WebCam manufacturers do not give the native res but
only the interpolated res. That is useless info for me.
Do not care too much about video or audio.
I can tell you a problem with this plan.
My webcam claims to do 1600x1200 and 30FPS. But, it doesn't
actually do that at the same time. It runs 1600x1200 at 5FPS.
Or, it runs 640x480 at 30FPS. And five frames per second, sucks!
They don't say in the advertisement, that it can't do the
1600x1200 and 30FPS at the same time. They're careful
to not say "1600x1200 @ 30FPS", which would commit them
to meeting both specs.
What you'll soon find, is if the webcam uses USB2, there are
limits to what you can "push" through the cable.
This is also influenced by the compression standard used. It's possible
my webcam offers uncompressed or MJPEG compression of the
image, which limits how much the image can be compressed and
the data rate reduced.
There are UVC (USB Video Class) cameras with H.264, and
there the compression ratio could be a lot higher, like
100:1. Then the cable is less of an issue. It doesn't
mean though, that the camera is superior in all respects.
So what you're looking for, is a camera that isn't limited
by the interface.
The other detail, is light sensitivity. If the scene isn't
lit by a halogen lamp, my camera will also reduce the frame
rate in order to gather enough light. It's a kind of exposure
control. And this is a serious limitation of most webcams.
The sensors used, are non-Sony, and they suck.
And that results in lots more 5FPS operation, than operation at
30FPS, and that is damn annoying.
When I read the side of the box, at the computer store, the
specs looked impressive. In actual operation, my webcam was
mostly a dud. The only good thing was autofocus, and that
mostly worked. From a theoretical perspective, the autofocus,
if left hunting for focus, would likely eventually wear out,
as a small motor is involved. So if the camera was left running
24/7 and a dynamic scene was present, it's hard to say how
long the camera would last, before the autofocus mechanism
wore out. That's really a function of how it's built, and
if it uses a motor and gears, then gears don't last forever.
*******
To give you some idea what may become more commonplace some day,
take a look at these.
http://www.ptgrey.com/products/flea3_usb3/flea3_usb3_camera.asp
FL3-U3-88S2C-C Color
# 8.8 MP Sony IMX121 CMOS, 1/2.5", 1.55 µm <--- AFAIK, that's pixel size
# Rolling Shutter with Global Reset
# 4096x2160 at 21 FPS
(Power Consumption 5 V, <3 W, via GPIO or USB 3.0 interface)
That's a USB3 interface, and the speed is still limited. The
deal there, is likely the readout at the sensor is clock-rate
limited. That's the equivalent of a DSLR camera shooting 21
full-frame pictures in one second (burst mode). But that
sensor is doing it continuously.
Uncompressed, the datarate there is close to 180MB/sec. By not
attempting to compress the image, that helps keep the camera
a bit cooler. Only the sensor is going to warm up, due to the
data rate involved. It would require a fair bit of compute
power, to compress a 180MB/sec stream.
If you read one of their technical notes, you can see it isn't
really a consumer ready kinda thing. But the tech is becoming
available.
http://www.ptgrey.com/support/downloads/documents/TAN2011005_USB3_Supported_Configurations.pdf
I thought it was an interesting datapoint, even if it isn't
ready to plug into Skype today.
That camera doesn't have autofocus, and the camera doesn't
even come with a lens. You purchase a C-mount lens separately,
and screw it on. I have a surveillance camera here, using a
similar concept, and I don't really think of screw mounts
as being that great. It wobbles a bit, and it's hard to
get it adjusted right. From an overall quality standpoint,
having the manufacturer fit a lens would be best.
Paul
