Getting 30fps from a webcam?

The last time I was fooling around with the settings on my webcam
I left them at 30fps with the auto exposure off and the gain / brightess / saturation down & shutter speed up full.
A few nights ago I imaged Mars and for the first time I got 30fps
perfectly without any of those annoying lines or compression.
I think this (along with the good seeing) is why I got a good end image.

I've often got the feeling that the webcam chip can get 'saturated' with light?
Often if I am in a rush and need to find the imaging target quickly I will
click the 'automatic exposure' box and let the camera switch to 5fps with
the gain going right up.
This obviously makes the planet jump right out and easy to find but, when
I then set it to a higher frame rate and lower gain, the quality is never as good and I have to settle for 15 - 20 fps so as to not get 'lines'

Has anyone any experience of this?
I'm of the opinion that you are better off keeping the settings
set at 30fps and all the gains / brightness etc levels down and to work 'up'
to a usably bright image, this way it doesn't over saturate the chip.

Either that or I'm gone totally bonkers.
What ye reckon?

Frank,

I would suspect something the opposite in relation to chip saturation. For example, with 30 fps, the maximum exposure you can have is 1/30 sec (obviously) whereas with 5 fps one can go up to 1/5 sec for the exposure or six times as bright. As a result, a slower fps can lead to chip saturation much easier.

Also, with 30 fps, I am certain you will be getting dropped frames as well as some sort of compression. I think the optimal rate is around 10 fps and this is a rate I have seen quoted quite often by Damian et al.

Of course, with firewire cameras, we have the priviledge of a true 30 or 60 fps and with no compression etc.

a slower fps can lead to chip saturation much easier

Yes, this is what I am saying. It's fine at 30fps but when I switch to a slow frame rate like 5fps and then go back to 30fps the quality of signal is worse.

Also, with 30 fps, I am certain you will be getting dropped frames

Nope, not many! one or two per capture ( from 2500 frames)
I put this down to the new laptop and keeping it clutter free for better speed.

as well as some sort of compression.

yes I presume there would be.

I think the optimal rate is around 10 fps and this is a rate I have seen quoted quite often by Damian et al.

for standard webcams?
I always use the fastest frps as the subject will allow.


:oops:

Also, with 30 fps, I am certain you will be getting dropped frames

Nope, not many! one or two per capture ( from 2500 frames)
I put this down to the new laptop and keeping it clutter free for better speed.

I have also tried defragmenting my hard disk for improved performance but I never did notice any improvement. My USB1.1 is the exclusive bottleneck in this game.

I think the optimal rate is around 10 fps and this is a rate I have seen quoted quite often by Damian et al.

for standard webcams?
I always use the fastest frps as the subject will allow.

Yes, for standard webcams such as the Phillips ToUCam Pro, the optimal rate seems to be around 5-10 fps due to the complete absence of compression.

I agree that it seems logical to use the fastest frame rate possible but personally I was getting dropped frames (easily 10-20%) as well as lower quality video.

5-10 fps due to the complete absence of compression.

Ok. That makes sense, no compression = more detail.
I'm going to have to go back and re think the settings I use to
see can I get a bit more detail.
As far as dropping back the frame rate, I guess I could run the capture longer to gain enough good frames.

5-10 fps due to the complete absence of compression.

Ok. That makes sense, no compression = more detail.
I'm going to have to go back and re think the settings I use to
see can I get a bit more detail.
As far as dropping back the frame rate, I guess I could run the capture longer to gain enough good frames.

Frank,

The only "limitation" is the 2 Gb file size limit that Windows imposes. As a result, I let the AVI build until I approach this limit.

Also, please have a look at a really neat little program called HandyAvi - www.astroshow.com/handyavi/handyavi.htm - which goes through an AVI and ranks all the frames from hightest to lowest quality. It is really sweet and allows you to construct a smaller AVI with really high quality frames and which you can use as input to RegiStax.