toucam bias frame

Hey
When taking a bias frame for the philips toucam what settings should i use?
The settings i have at the moment are
Frame rate = 5fps
auto exposure = off
gain = ?????
shutter speed = set to highest (can't completely disable it)
Auto White balance = ON
Brightness = set to highest
contrast = set to lowest
gamma = set to lowest
saturation = set to lowest
black and white = off (camera modified with b&w chip)

I am guessing at the moment that it is possible that they should be set to the same values that will be used when taking the light frames?

Cheers
Mike

Mike - if you're talking about a "traditional" bias frame for calibration purposes, the bias frame is the same as a dark frame but taken at the shortest possible exposure time.

They are used if you want to scale your dark frames.

For example, if you are taking light frames, but do not have an exactly corresponding dark (same exposure duration and CCD temperature) a bias frame can be used to scale your next best dark. In the case of MaximDL, it will use the bias frame to scale the next-best-dark frame and then use the resulting scaled dark.

So, in view of this, I don't think the likes of brightness, gamma etc should make any difference.

That said, I'm predicating all this on the bias frame *you* are talking being the same as the bias frame *I* am talking about.

As an FYI, I don't use bias frames. I just make sure my darks are at the same exposure duration as my lights - hence bias frames are not required.

Hope that helps...
Dave

Cheers Dave
The bias frame i am thinking of is used for image calibration, my understanding is that it helps to compensate for read-out noise and interference from the computer. In fact you hit an interesting point that i was unsure of, is there in fact 2 distinct types of bias frames?
When i set the camera up to take a bias frame (away from any light), and i start adjusting the parameters i do tend to get a "different picture" for example if i take gain from full to zero the picture appears less noisy which is to be expected i guess. I am wondering how much the software affects the bias or any calibration frames.

Regards,
mike

Mike - the bias is a calibration frame that determines the read noise of the imager. If additional "noise" is being introduced by the PC, I'm not sure how you would compensate for that.

Its odd that you're getting some different looking images depending on other settings of the camera. I'm not that familiar with CMOS technology (assuming that's what the toucam uses) so it could be a factor.

One things is for sure though, if you have darks taken at the same temperature and exposure duration as your lights, there's no need for a bias frame.

One other thing that strikes me is that its possible, presuming the toucam is an electronic shutter type camera, that any images you take may be affected by any ambient light - so make sure the imager is competely light-tight and/or try and take the bias in as dark a room as possible.

If you use maxim to look at the images (or similar software), look at the pixel value differences between images that look different. Even though the images "look" different, the pixel values may be very similar and hence you'd have little to worry about.

And sure, you have the right idea about bias. I'm sure there's only one - but its not really going to help too much if "computer" noise comes into play.

If your gain is set at a typical value when you image, that's the value I'd use for the bias. Don't worry about it "looking" noisy. I could show you my uncalibrated images and you'd be horrified! But when they have flats and darks applied, they come out gleaming

Hope that helps a little bit more!
Dave

Hey Dave
Yea i certainly take your point on this, i was going to post some images of what i see but as you suggested i have tried darks since my last post and i think your correct and at least the image appears ok when stack and processed with the darks.

When taking the image via the Toucam i use wxAstrocapture, this shows a live histogram which helps me to judge my gain settings.

I managed to get some shots of Jupiter, but man its taking a bit of work to figure out how to stack the RGBs e.t.c. The seeing was good and i was expecting to get some decent detail.
I have some detail in the L frame and R frame, a bit in the green, with the blue is weak. I don't think i was giving the scope long enough to cool down so my raw data isn't great and also DEW building up on Powermate and Secondary mirror didn't help. Anyhow in a nutshell I have some other issues to overcome and I may need start a different thread on these!!!!

Thanks Again
Mike