CPU load when stacking images

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glauria
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Joined: Wed May 30, 2018 7:15 pm

CPU load when stacking images

#1

Post by glauria »

I was asked general question about the loading of the computer's CPU as one accumulates images during a live stack:

When one does live stacking for EAA, and a new image comes in, I know it will calibrate that image… But then does it just add that one image to the existing stacked image? Or does it have to re-stack all of the previously calibrated images into a new stack?

I’m wondering how much processor and memory are used as the stack grows throughout the evening. Basically, is adding a new image to the stack the same amount of effort for each new image, or does it grow linearly in it’s demand throughout the evening?

...meaning that as the stack gets larger, does it require more and more processing with the CPU? My guess is that it doesn't and that the situation that would put the most load on the CPU is if one is trying to capture images at a high rate with a large camera for example, when one is trying to do lucky imaging for planets, solar.

Thanks,
-Gene
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admin
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Re: CPU load when stacking images

#2

Post by admin »

Hi Gene,

the amount of calculation is the same for each added image. SharpCap doesn't redo the whole stack from scratch each time, as that would - as you say - take longer and longer as you added more images and soon might take longer than it takes for a frame to be captured...

The biggest CPU load for live stacking that is required tends to be the star detection (which is needed for alignment). The various sharpening and noise reduction options can also consume a lot of CPU, but of course those are optional.

cheers,

Robin
glauria
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Joined: Wed May 30, 2018 7:15 pm

Re: CPU load when stacking images

#3

Post by glauria »

Thanks Robin,

I'm basically trying to figure out whether a Celeron N-5095 processor will have the capacity to work well with SharpCap for doing deep sky imaging.

The advantage of using a processor like this is that it is rather inexpensive, and dissipates a modest amount of power which is advantageous for remote observing not to mention that it runs on 12V. The higher performance computers dissipates twice as much power and runs on 19V.

-Gene
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Re: CPU load when stacking images

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Post by admin »

Hi Gene,

depends on the resolution of your camera (16 megapixels will use 4x as much CPU as 4 megapixels) and the amount of processing you intend to do. Also you need to think about the exposure lengths you are planning on. If you will be taking 30s exposures then you can afford for 15s to be taken stacking each frame. If you plan on 8s exposures then 15s processing is a problem!

Although SharpCap is - as a whole - multithreaded, the stacking is single threaded, so the single thread performance score on CPU benchmark should give a reasonable guide to stacking speed.

Do check on the voltage requirements of the other computers - for instance I have an Intel NUC. It comes with a 19V power supply, but if you read the documentation carefully, it will run off 12V too.

cheers,

Robin
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