Author Topic: A cropping question  (Read 8004 times)

Offline joelshort

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A cropping question
« on: 2015 March 08 15:31:06 »
I am processing an HaRGB galaxy image, and unfortunately I forgot to crop the Ha image when I cropped the RGB images so the scale is different.  I'm well down the path of processing the RGB at this point.  Is there a way that I can crop the Ha image so it matches the crop and scale of the RGB image?
Joel Short
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Offline Don

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Re: A cropping question
« Reply #1 on: 2015 March 08 15:49:34 »
Yes, the DynamicAlignment tool will do that.  Select the smaller image as the reference and the larger as the target.  You will need to pick some stars to align the target to the reference image, so display the images side by side at the same scale.  You then pick a star in the reference image by clicking, and the tool tries to find the matching star in the target image.  If it picks the wrong target star, you can drag the selection box to the correct star.

After matching at least three or four stars, click Execute.  The process will rotate, translate and crop the target image to match the geometry of the reference.

Don


Offline joelshort

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Re: A cropping question
« Reply #2 on: 2015 March 08 15:57:07 »
Thanks Don.
Joel Short
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CFF135 f6.7, SV80ST, G3-16200M, QHY163M, QHY183M

Offline RickS

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Re: A cropping question
« Reply #3 on: 2015 March 08 16:49:00 »
If you still have one of the original RGB files you cropped you can go back through the history and drag and drop a DynamicCrop process icon from it.

Offline msmythers

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Re: A cropping question
« Reply #4 on: 2015 March 08 16:51:40 »
Joel,

A very simple way is to use the StarAlignment tool. Select your cropped image as the reference and drag the New Instances triangle to the image you want aligned. Defaults generally work fine unless the image is very noisy.

Mike

Offline joelshort

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Re: A cropping question
« Reply #5 on: 2015 March 08 16:54:48 »
Mike, that was super easy.  Thanks!
Joel Short
www.buckeyestargazer.net
CFF135 f6.7, SV80ST, G3-16200M, QHY163M, QHY183M

Offline msmythers

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Re: A cropping question
« Reply #6 on: 2015 March 08 17:36:51 »
Glad it helped Joel. It seems most tools in PI have so many great uses that aren't the normal way of using them.


Mike

Offline Don

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Re: A cropping question
« Reply #7 on: 2015 March 09 09:59:57 »
Joel,

A very simple way is to use the StarAlignment tool. Select your cropped image as the reference and drag the New Instances triangle to the image you want aligned. Defaults generally work fine unless the image is very noisy.

Mike

That is very good to know.  I didn't know StarAlignment would crop a target image.  I have been doing it the hard way.

Thanks,

Don

Offline RickS

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Re: A cropping question
« Reply #8 on: 2015 March 09 17:29:11 »
I don't think that using StarAlignment for cropping is ideal.  It's going to interpolate the image again and the less you mess with the data the better.  I'd only use it as a last resort...

A simple option is to save a copy of the process icon when you use DynamicCrop the first time.  Even if you forget to do this you can usually drag a copy from the History of one of your cropped images.

Cheers,
Rick.

Offline joelshort

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Re: A cropping question
« Reply #9 on: 2015 March 09 17:34:32 »
Rick,
"Even if you forget to do this you can usually drag a copy from the History of one of your cropped images."

I tend to process images over days, especially now when I'm still learning PI.  If I have previously closed the images that I cropped, is there any way to recover the DynamicCrop instance that I used? 
Joel Short
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CFF135 f6.7, SV80ST, G3-16200M, QHY163M, QHY183M

Offline RickS

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Re: A cropping question
« Reply #10 on: 2015 March 09 17:57:57 »
I tend to process images over days, especially now when I'm still learning PI.  If I have previously closed the images that I cropped, is there any way to recover the DynamicCrop instance that I used?

Unfortunately not.  You'll have lost the history.

I process images over days, or even months, and I find it really useful to save the project and resume it each time.  It's not uncommon for me to decide long afterwards that I want to roll back some of my processing and redo it differently.  Having the history available makes that much easier.

Cheers,
Rick.

Offline joelshort

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Re: A cropping question
« Reply #11 on: 2015 March 09 18:01:13 »
What do you mean by "save the project and resume it each time"?  I'm assuming that's the "save project" option in the file menu.  What all does that save?  Open process icons, images, etc?  If so, that would be very handy.  I didn't notice that before.  So much to learn...
Joel Short
www.buckeyestargazer.net
CFF135 f6.7, SV80ST, G3-16200M, QHY163M, QHY183M

Offline RickS

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Re: A cropping question
« Reply #12 on: 2015 March 09 18:15:40 »
What do you mean by "save the project and resume it each time"?  I'm assuming that's the "save project" option in the file menu.  What all does that save?  Open process icons, images, etc?  If so, that would be very handy.  I didn't notice that before.  So much to learn...

It is incredibly handy, Joel!  The Save Project and Load Project options allow you to save and restore your whole session with images, history, process icons and workspaces.  The only disadvantage is that a project can grow quite large.

Cheers,
Rick.

Offline joelshort

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Re: A cropping question
« Reply #13 on: 2015 March 09 18:22:31 »
That's so great.  Thanks for bringing that to my attention. I'll be using that from now on.
Joel Short
www.buckeyestargazer.net
CFF135 f6.7, SV80ST, G3-16200M, QHY163M, QHY183M

Offline msmythers

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Re: A cropping question
« Reply #14 on: 2015 March 09 19:16:21 »
Rick,

I did a quick experiment with an image first cropped and then I used the cropped image as the reference for StarAlignment to crop the original. I then ran Statistics on both final images. I was only using default values for StarAlignment. The only slight difference were in the Min and Max values and those changes were very slight.

I agree that if you have the old DynamicCrop icon use it but if you have an image where you don't the StarAlignment method is simple and very precise.


Mike