SPC900 users - check this!

[teh_orph]

Hi there,

I've been using my new SPC900 for the last few weeks for imaging things like planets and the moon. When playing with IR filters in my home I noticed something that I hadn't noticed when outside (because I was probably too busy!) - changing the capture framerate from 15 to 20 frames per second halves the resolution!

For reference, the pics below were captured with YUV2, 640x480, fixed exposure settings, fixed white balance, sharpening off. Changing only the frame rate within the Philips dialog gives this change:

Top is 20 fps, botton is 15 fps

Left is 15 fps, right is 20 fps.

Apologies for the JPEG compression.

I've noticed that for all sub-20 frame rates the image is much higher quality and there are no significant changes (other than noise levels) going from 5-15. The same applies 20-60 - but it's the 15->20 transition which halves the apparent resolution! Looking around teh interwebs it seems that the driver just resamples the image to give a 640x480 image in order to meet the USB 1 bandwidth restriction.

Here are the full res pics if you'd like to look. They each show split images, showing what it would look like if sharpening were on versus if it were off.

http://img543.imageshack.us/img543/3158/16163418.jpg

http://img593.imageshack.us/img593/5831/85559557.jpg

http://img179.imageshack.us/img179/6815/55535567.jpg

http://img179.imageshack.us/img179/5608/49633899.jpg

So to summarise - if you're using YUV2 and a Philips SPC900 then make sure you keep your frame rate below 20 fps!

[Sam]

Excellent, thanks for posting this. I think a lot of people will find this very useful.

[Breakintheclouds]

Thanks for the warning - I just bought an SCP900 and I doubt I'd ever have spotted that. So just to get this clear: is 640x480 okay as long as the frame rate is below 20?

[teh_orph]

That's right. I think the framerate that the switch happens may depend on the pixel format chosen, but certainly YUV2 (the highest quality) will switch at 15->20 so keep your capture rate below 20 if you value your image quality!

Also I'd recommend turning off the image sharpening option too if you want a more natural looking picture (ie no ringing on sharp edges).

[Dave Smith]

Thanks - that's useful to know.

Dave

[iamzoso60]

Thanks for the advice. I will give it a try if we ever get clear skies again!

[beamish]

TBH why would you want to go for 20fps or above anyway knowing that compression artifacts were always going to come into play? The SPC900 , even the original genuine ones , not the re-flashed versions, would show horrendous compression artifacts beyond 15fps.

[riklaunim]

You can always try some true USB 2.0 webcams like some MICROSOFT LIFECAM webcams.

[teh_orph]

TBH why would you want to go for 20fps or above anyway knowing that compression artifacts were always going to come into play? The SPC900 , even the original genuine ones , not the re-flashed versions, would show horrendous compression artifacts beyond 15fps.

Well there's always the sun and the moon which are much too bright to capture properly

Also I've found the high capture rates useful during poor seeing eg whilst it's windy.

But yes, it's not my webcam of choice. I think I'm gonna do a guide to show how to convert a PSEye for use for astrophotography. I can't see any amp glow with that sensor and it (out of the box) can do exposures of up to ten seconds.

[beamish]

well fair enough, but you could always use a much shorter exp and crank the gain right down. for solar use a green filter ( as well as the solar filter of course) and for Lunar use an ND filter or a red or green filter and process as a mono ?

I suppose it's case of recognising it's limitations as a USB1 w/cam.

The lifecam HD and logitech Pro 9000 are better in that respect but far more expensive, but not as good for planetary work due to CMOS chip.

Just my 2pworth that's all not rubbishing it cos I still have one and a great intro to imaging

[riklaunim]

but not as good for planetary work due to CMOS chip.

Modern CMOS with good electronics isn't noticably worse than ancient CCD (ICX098 that is) used in astro-webcams That is if they use a modern CMOS. Highly priced Microsoft or Logitech/Creative HD wecams shoud have those modern ones.

[beamish]

just talking from experience , in particular the 9000 pro, great for lunar but was outdone by the SPC900NC

[teh_orph]

just talking from experience , in particular the 9000 pro, great for lunar but was outdone by the SPC900NC

With your CMOS cameras, do you see the rolling shutter effect at all? (where each scan line is captured at a slightly later time than the previous)

If not then I might be interested in getting one

[beamish]

Speaking only for myself here, I'd say NO, not that I ever recall, with the exception of the QHY5 where this venetian blind effect can be seen at high frame rate/exp/gain combos

re my quote above I should add:-

"....great for lunar but was outdone by the SPC900NC , with respect to planetary."

[rwg]

This is kind of hard to get into the right words, but there is also a blurring between frames when the SPC900 is used at high frame rates. Even at 10-15 fps, each frame isn't an independent image but is some mixture of the last frame and new data from the camera.

I found this while getting SharpCap to work with the SPC900 is LX mode - I was expecting to have to send the signal to stop the LX exposure and just grab the next frame as to get the result. Doesn't work out like that - the next frame is usually just a dim image, and the frame 1 or 2 later has the full long expsure image in it! In the end I had to look at each of the following 5 frames and choose the brightest one as the result...

Anyway, I'd second the recomendations to keep the frame rate as low as possible on this camera. A nice way to show the results is to turn the gain, exposure and brightnes up near to max so you can see the hot pixels on the image (you're sure to have some - all my SPC900's do). Then play with the frame rate and see how much sharper the hot pixel dots are at 5fps than the higher rates.

Robin

[michaelmorris]

From my experience, 10 fps is the optimum frame rate to use with the Toucam Pro/SPC900. I find it is the fastest frame rate I can use without any noticeable compression artefacts. 5 fps give slightly sharper images indoors, but for astro work, in all but the very good seeing conditions, this is counteracted by blurring due to the slow frame rate.