Difference between revisions of "FAQ"

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* When using the [[Align and Combine]] tool for alignment, make sure that you select "Save each file" in the "Output mode" option. This should give you three files that each start with "align_".
 
* When using the [[Align and Combine]] tool for alignment, make sure that you select "Save each file" in the "Output mode" option. This should give you three files that each start with "align_".
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| I have selected "Save each file" for the aligning step, but Nebulosity doesn't seem to be saving my newly aligned files.
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* If you have attempted alignment already, Nebulosity will not overwrite your files from your first attempt. Delete the files "align_" files from your previous attempts before you try to re-align.
 
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| I thought I aligned my images, but when I combine them using LRGB Synthesis, they don't look aligned.
 
| I thought I aligned my images, but when I combine them using LRGB Synthesis, they don't look aligned.
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* Try using the [[Create 3-colour images#Adjust_Color_Background|Adjust Color Background]] tool.
 
* Try using the [[Create 3-colour images#Adjust_Color_Background|Adjust Color Background]] tool.
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| There are large white spikes on one or more of the stars in my image.
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* This is an effect known as "pixel bleed" or "saturation bleed". See [http://stardial.astro.illinois.edu/cosmics.html here] and [http://www.eso.org/~ohainaut/images/imageProc.html here] for more information. In brief, these lines are caused by too many photons hitting a pixel in the detector. Unfortunately, these lines cannot be removed in Nebulosity. If you have access to an advanced image editing software, such as Photoshop, you may try your hand at cloning them out there. If your images have pixel bleed, your best bet is to take steps to avoid it in your next observations with iTelescope. One method you can use is to take several shorter exposures with each of your filters and then stack them. Talk to Professor Reid or your TAs for more information.
 
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| Nebulosity will not open my files.
 
| Nebulosity will not open my files.

Latest revision as of 20:28, 23 January 2015

Image Editing FAQ

Problem Solutions

I can't see any features in my image.

  • Try zooming out to see your entire image. You may be zoomed in on a small patch.
  • Use the Digital development or Levels and Power Stretch tools to bring out the features in your image.
  • You can also try changing the scale of your image. Go to Image -> Scale Intensity -> select "Log" and then hit "Done". This is particularly helpful for images of nebulae.
  • You might need a longer exposure using i-Telescope.
When I try to make a three-colour image, I get the message "Cannot use this frame as the number of pixels does not match. Please align frames first."
  • Make sure each of your filters (and filter stacks) has been aligned using Align and Combine.
When I align my three filters, I only get one file at the end, not three.
  • When using the Align and Combine tool for alignment, make sure that you select "Save each file" in the "Output mode" option. This should give you three files that each start with "align_".
I have selected "Save each file" for the aligning step, but Nebulosity doesn't seem to be saving my newly aligned files.
  • If you have attempted alignment already, Nebulosity will not overwrite your files from your first attempt. Delete the files "align_" files from your previous attempts before you try to re-align.
I thought I aligned my images, but when I combine them using LRGB Synthesis, they don't look aligned.
  • When using the Align and Combine tool for alignment, make sure that you select "Save each file" in the "Output mode" option. This should give you three files that each start with "align_".
  • When performing the "aligning" steps, make sure that you are picking two stars that are non-saturated (that have a value much less than 65,000 when you hover over them) and that are far away from each other on the image. Picking stars that are close together may lead to poor alignment.
The background of my image isn't black.
There are large white spikes on one or more of the stars in my image.
  • This is an effect known as "pixel bleed" or "saturation bleed". See here and here for more information. In brief, these lines are caused by too many photons hitting a pixel in the detector. Unfortunately, these lines cannot be removed in Nebulosity. If you have access to an advanced image editing software, such as Photoshop, you may try your hand at cloning them out there. If your images have pixel bleed, your best bet is to take steps to avoid it in your next observations with iTelescope. One method you can use is to take several shorter exposures with each of your filters and then stack them. Talk to Professor Reid or your TAs for more information.
Nebulosity will not open my files.
  • The files you download from itelescope.net are usually compressed .zip files. You will need to extract the FITS files from the compressed folder in order to open them in Nebulosity. To do this, use your file explorer to navigate to the folder where you have saved your itelescope.net files. Double-click on the .zip file. Select the file inside and click "Extract". This will move the FITS file into the folder you have specified. You should now be able to open it with Nebulosity.

Observation Related FAQ

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