How to Process Your Own Colour Images from Hubble Data

Step-by-Step Guide

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   Step 1: Open the Hubble Legacy Archive at http://hla.stsci.edu/.

   Click "Enter Site".
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   Step 2: Locate the search box and the list of example searches below it.

   You can search for objects by a number of criteria:
   New General Catalogue (NGC) numbers, IPPPSSOOT names, proposal IDs, location, and even names such as "Eagle Nebula" which are referenced against the NASA/IPAC Extragalactic Database (NED)or the SIMBAD Astronomical Databasewhen necessary. ,, These cameras give the best images for compositing into coloured final products. ,, This should return 62 results. ,, You can expand an image by clicking "Interactive Display" under a thumbnail., The second last item in the name (f814) is the filter used to take the image.
   
   The item directly before it (wfpc2) designates it was taken with the Wide Field and Planetary Camera
   2. , The three images will later be combined to each represent one of the three colours in an RGB (Red, Green Blue) image.
   
   An example of a good set of filters would be WFPC2 F450W (Blue), WFPC2 F555W (Green), and WFPC2 F814W (Red). ,, Download and install either the Windows or Mac version depending on your operating system. , For now, select hst_05237_02_wfpc2_f814w_wf_drz.fits. , Play with some of the buttons and notice the changes to the image preview. ,, Find the "Stretch" drop-down which contains a number of pre-sets and select Log(Log(x)). , Change the file name to match the filter (for example, save hst_05237_02_wfpc2_f814w_wf_drz.fits as f814.tif). ,, For now, use f814w.tif and call the layer f814w. , In Photoshop you can use File
   -> Place to accomplish this easily (be sure to rasterize the placed images). ,,,, Then hide it by clicking the eye beside the layer name. ,,,,,, Then use the crop tool to loose everything else.
   
   You may need to rotate your selection or all three layers to get the region you want––just remember that all three layers must remain selected so that you don't undo your work from above. ,,,, It should automatically set the size to the size of the image you copied; the only thing you need to change is the bit depth of the image from 16bit to 8bit and the name of the image to the name of the layer you copied. (If you copied the layer called f814w, call the image f814w.) ,, At this point you can close the original three layer image. ,,, If the merge option is greyed out, your images are either not flattened or are not 8 Bits.
   
   You can fix this in the Image
   -> Mode menu. ,, For this guide, it should be Red: 814, Green: 555, Blue:
   336. , The outcome of the image will be affected by the filters chosen, and the settings used in FITS Liberator. , Play with your results and you can make something truly beautiful.
   
   The image to the right is of NGC 6357 and was made using WFC F658N for blue, WFC F660N for red, and an average of the two for green using the same method with heavy post-processing.
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   Step 3: For this guide

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   Step 4: enter "NGC 604" in to the box

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   Step 5: which is the New General Catalogue identification number for the "The Triangulum Emission Garren Nebula".

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   Step 6: Click the advanced search link and select only the WFPC2 (Wide Field and Planetary Camera 2)

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   Step 7: WFC3 (Wide Field Camera 3)

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   Step 8: and ACS (Advanced Camera for Surveys) under Instruments.

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   Step 9: Change the Data Product to "Combined (Level 2)".

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    Step 10: Click Search.

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    Step 11: Locate the "Images" tab to sort the data as thumbnails for easy viewing.

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    Step 12: Explore the results to get a feel for the data in the HLA.

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    Step 13: Locate the fourth image in the result for the search of NGC 604 above and you will find the file name "hst_05237_02_wfpc2_f814w_wf" below it.

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    Step 14: Locate three separate filtered images to create your composite.

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    Step 15: To download your images

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    Step 16: right click the "FITS-Science" link and "Save As" or you can click it to add the items to your "Cart" and download them in a batch by clicking the "Cart" tab at the top of the search results.

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    Step 17: To work with FITS files you will need a small free application called FITS Liberator.This can be downloaded from http://www.spacetelescope.org/projects/fits_liberator/download_v301/.

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    Step 18: Open FITS Liberator and navigate to one of the files downloaded earlier.

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    Step 19: Take a look around the software at the information and the different changes you can make.

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    Step 20: Click the "Reset" button on the left to return the image to its native form.

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    Step 21: For now

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    Step 22: you are just going to use a simple stretch on the images before you save them.

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    Step 23: Click "Save File" and save the TIFF file to an easily accessible location.

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    Step 24: Do the same thing for the other two FITS images.

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    Step 25: Open your first image in your editor ensuring the layer is named the same as the file.

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    Step 26: Place your second and third images above the first in their own layers; again

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    Step 27: ensure the layers are named for the files.

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    Step 28: Select your top layer and zoom in on an area with a number of stars.

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    Step 29: Lower the opacity to between 50% and 60% so that you can see stars from the layer below.

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    Step 30: Look for stars that appear in both layers and nudge the top layer to make things line up.

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    Step 31: Return the top layer to 100% opacity.

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    Step 32: Select the middle layer and lower the opacity to between 50% and 60%.

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    Step 33: Hold the shift key to select both the middle layer and the hidden top layer (these images are now lined up so we want to move them together).

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    Step 34: Locate a star that appears in the middle and bottom layers as a reference to line things up.

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    Step 35: Return the middle layer to 100% opacity and unhide the top layer.

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    Step 36: Use the shift key to select all three layers.

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    Step 37: Use the selection tool to select an area of the image that you want to work with.

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    Step 38: Rotate the final product however you like.

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    Step 39: Select your top layer in Photoshop and click Ctrl+A on your keyboard to select the entire canvas.

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    Step 40: Click Ctrl+C on your keyboard to copy the entire contents of the layer.

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    Step 41: Click File -> New or Ctrl+N to create a new image.

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    Step 42: Paste the copied layer to the new image using Ctrl+V or by going to the "Edit" menu and then "Paste".

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    Step 43: Do the same thing for the other two layers until you have three new images

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    Step 44: each with one layer.

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    Step 45: Flatten each image by right clicking the layer and selecting "Flatten".

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    Step 46: On your third image

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    Step 47: open the "Channels" window from the "Windows" menu.

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    Step 48: Click the menu icon in the top right hand corner of the channels window and click "Merge Channels".

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    Step 49: Select "RGB" for the mode and 3 for the number of channels and click OK.

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    Step 50: Set your lowest filter as blue

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    Step 51: the middle as green

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    Step 52: and the highest as red.

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    Step 53: Click OK. You will be instantly presented with a colour image.

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    Step 54: Use the level and curve adjustments on the various channels and the full image to reach a product you're happy with.

Detailed Guide

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