Image quality and ROI.

Discussions of using SharpCap for Planetary Imaging
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Oakley Matt
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Joined: Sat Jun 05, 2021 7:40 am

Image quality and ROI.

#1

Post by Oakley Matt »

I think I know the answer to this but just wish to check.

If I take an image of the moon using Sharpcap with my camera without adjusting the frame size I get an image.

However, if I adjust the frame size, for arguments sake, so the same size image as previously taken were made up from 4 frames, do I just get a smaller image (1/4 the size) of a corner of the previous target area with no adjustment in image quality?


Or to put it another way, if I create a mosaic of the moon, made up from 4 smaller images, is it likely to be any better quality than a single image where there has been no adjustment of the frame size?
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admin
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Re: Image quality and ROI.

#2

Post by admin »

Hi,

to make this clearer I'm going to add some specifics...

Let's assume your camera is 4000x3000 pixels and you can see the whole of the moon in view at once when using your telescope. So, you capture an image of the moon.

Next, you set the camera to only capture an area of 2000x1500 pixels. Now in that smaller area the whole moon will not fit in view, so you take 4 panels as a mosaic.

Is the second going to give higher quality than the first approach? No - they will be pretty much identical quality.

However, a mosaic can be useful in other situations, like...

1) You add a barlow lens to increase magnification (or use a longer focal length telescope) - now the whole of the moon doesn't fit in view of your camera. You take a mosaic and stitch the panels together and you can potentially get a higher quality image than with a single panel without the barlow lens

2) You have a smaller sensor camera which doesn't allow the whole of the moon to fit in view, so the only option to get a whole moon image is to take a mosaic.

Hope that helps,

Robin
Oakley Matt
Posts: 9
Joined: Sat Jun 05, 2021 7:40 am

Re: Image quality and ROI.

#3

Post by Oakley Matt »

Thanks. Pretty much as I figured.
Oakley Matt
Posts: 9
Joined: Sat Jun 05, 2021 7:40 am

Re: Image quality and ROI.

#4

Post by Oakley Matt »

I guess also if you adjust the ROI so you’re capturing a smaller area you’ll be able to get more FPS, which might actually give a better quality image once processed.
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Re: Image quality and ROI.

#5

Post by admin »

Hi,

the FPS tends to matter most for targets that change relatively quickly (Jupiter rotation or solar prominences). For relatively slowly changing targets like the Moon or Saturn, you can always capture for longer to get enough frames, and reduce the exposure as far as required to freeze the seeing in each frame.

cheers,

Robin
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