Video used to capture?

[PBD]

So I have been reading and something has started to confuse me. People are talking about using video and using a web cam to capture images.

This this because a video is more or less images out back to back? Don't you lose image quality when in video mode?

If someone could explain using video, that would be amazing!

[Nova]

I use a webcam to capture images. Ill normally take footage of around 1000 frames (depends on conditions and target) then ill use software to sort through the frames discarding ones that arent as good as my set benchmark frame. It will then align and then stack the remaining frames on top of one another. As an example you may catch certain detail of a target in frame 20 and different detail in frame 30 so when stacked you get the detail from both frames. (obviously normally there are a lot more frames) Hope this helps.

[steelfixer]

Steve has summed it up perfectly.

I also use a Samsung SBC 2000 video camera for deep space stuff.

These are amazing survailence cameras that integrate loads and loads of frames inside the camera itself before transmitting them as one image, a bit like extending the exposure time.

You can still treat the AVI as you would with a standard web cam or you can convert the AVI frames into single bitmap images and then process them in DSS along with darks, flats ect.

[themos]

Don't you lose image quality when in video mode?

It depends on the camera. With some, you are restricted to 5 or 10 frames per second before compression starts ruining your images. With other, more expensive ones, you can go up to 30fps or 60fps.

[Nova]

I like that idea Steelfixer, must take the strain off the laptop processor. Did you need to do an LX style mod for DSO's? Good price too. USB compatible? or is it a serial connection?

Sorry to go a little off topic

[The Bat]

If you have ever tried to observe a planet through a telescope you will have seen that the image is not stable, but wobbles and ripples due to atmospheric turbulence. Periodically, though, the image will stabilise allowing details to be seen. The use of a webcam capitalises on these moments of good seeing. Capturing a video sequence is like taking thousands of single frame images, and in some of those frames, the image will be much clearer than in others.

The software referred to above (usually Registax) is capable of sorting frames by quality, based on a reference image picked by the user. The frames are ranked in order, meaning bad frames can easily be discarded. The good frames are then stacked and processed. Stacking increases the signal to noise ratio, bringing out the detail.

A single video frame is not much to look at, but by the time hundreds or thousands of frames are stacked together, it produces some amazing results.

Rachel

[steelfixer]

Hi Steve

No mods it does this straight out of the box.

You need a video grabber, I use a usb dongle which of the name escapes me at the moment. They do sell these on Ebay for about £10.00 but my advice is to get a genuine one from the official web site about £19.00 as some of the ones on ebay are counterfiet and do not work.

The camera connects to the dongle via a coaxial cable.

You will also need a 12 volt power supply.

You can also connect it straight to a TV if you want and have your very own live show.

Hope this helps

Graham

[PBD]

With my 1dmk4 I can shoot in H and I think at 30fps. How do I expose for the video? High ISO?

[Nova]

For my spc the exposure is adjustable in the capture software (sharpcap)

Thanks steelfixer. I may look into that at some point

[PBD]

Can I just record to a memory card and then import to a computer latter?

[Nova]

Not with the camera I use, you need to see the object your capturing to adjust focus, exposure etc etc. Unless you mean a memory card connected to your laptop? That will work fine. AVI files are normally quite large around 500Mb for 1000 frames at 10fps on my system

[steelfixer]

Take a look at the video forum. You will find it in the science section.

[todd8137]

It depends on the camera. With some, you are restricted to 5 or 10 frames per second before compression starts ruining your images. With other, more expensive ones, you can go up to 30fps or 60fps.

ermm i use 20 fps just about all the time with my Philips web cam and it works out well for me

[themos]

Which Philips webcam are you running at 20fps?

From ToUcam Tutorial, I read the data rates needed for the ToUcam Pro (or any 640x480 camera at 8 bits)

dr[fps=5] = 35.15625 MBit/s

dr[fps=10] = 70.3125 MBits/s

dr[fps=15] = 105.46875 MBit/s

dr[fps=20] = 140.625 MBit/s

dr[fps=25] = 175.78125 MBit/s

dr[fps=30] = 210.9375 MBit/s

A USB1.1 camera cannot exceed 12 Mbit/sec so even at 5fps some compression is necessary. At 20 fps you need to compress 11:1 or more and I'm pretty sure that you are losing significant data at that point.

[themos]

By the way, you can see now why people do the RAW modification on their colour CCD webcams. Remember that in a colour camera, each pixel has a green, red or blue filter in front of it so that the pixel captures light in only those colours. The webcam electronics then combine the information from nearby pixels of different colour to give a triplet RGB value for each pixel. That's 24 bits per pixel (3 * 8). But the actual original information was only 8 bits per pixel. So, in standard colour mode, the electronics are expanding 8 -> 24 and then compressing 24 down to whatever will make it through the 12Mbit/s limit, according to frame rate. So why not just send the original 8 bits? That's what the RAW modification to the firmware does. If you divide the 35.15625 number by 3 you get something just under 12Mbit/s which means you can safely transmit all 8 bits without any compression. The price you pay is that the image looks a bit strange and needs post-processing to turn it into a proper colour image. But that can be done inside the computer where we're not restricted by the USB bandwidth. Furthermore, it means you can shoot at higher frame rates and still have lossless compression (but I don't know what compression the camera actually uses in that case, maybe it's a lossy compression)

[Nova]

Interesting stuff Themos. Is the raw mod hard to do on a flashed spc880? Also is it reversable?

[themos]

The raw mod is purely a software mod. No screwdrivers needed!

It is reversible but there is a degree of risk. I haven't heard of anyone "bricking" their webcam yet but it is possible that the "flashing" of the webcam chip could go wrong.

I have done it to a ToUCam Pro PCVC740K and undone it.

The consensus, I think, is that the mod will only show benefit when you have the best seeing and you're trying to get that extra bit of performance out of your kit.

[Nova]

ok, ill look into that. Thanks.

[todd8137]

Interesting stuff Themos. Is the raw mod hard to do on a flashed spc880? Also is it reversable?

i have run mine in all modes in one night flashing and re flashing ect i used

WcRmac - Description

the raw mode is not great unless its real clear ,and good both my toucam and Phillips 880 are both flashed to the same you can back the original software up first then flash its not for the faint minded,my mates have done this here on sgl

heres a video i did a while ago at 30 fps flashed to special factory settings with my 12"reflector it does tho make the gain and expo go a bit crazy but it does make a difference

heres the video at 30fpsuse in the phillips

[todd8137]

Which Philips webcam are you running at 20fps?

From ToUcam Tutorial, I read the data rates needed for the ToUcam Pro (or any 640x480 camera at 8 bits)

A USB1.1 camera cannot exceed 12 Mbit/sec so even at 5fps some compression is necessary. At 20 fps you need to compress 11:1 or more and I'm pretty sure that you are losing significant data at that point.

thanks the web cam is flashed to special factory settings via wcrmac tools,heres a video at 30 fps with the Phillips flashed

if it was dropping frames the video would show bad play back ?

[themos]

flashed to special factory settings

I am confused by this.

[todd8137]

I am confused by this.

this video will answer your confused state or not