Thanks to Giuseppe for calling attention to the possibility of using the HubblesHiddenProcessing video to discover how to import and combine Hubble images. I have also been trying to learn how to do this. I tried it.
I obtained the two images from the Hubble Legacy Archive. They are images of NGC1763 with filenames
HST_9419_03_ACS_WFC_F658N_sci.fits
and
HST_9419_03_ACS_WFC_F660N_sci.fits
The numbers 658N and 660N refer to wavelengths.
I opened them in PixInsight and following the video, applied an identical crop and rotation to both. Then there is a bit of the video that goes by very rapidly where one has to reset the identifiers for the two images, with the 658n image reset to R and the 660n image reset to B using the Image --> Identifier dialog. Then it appears that one can assign colors to the wavelengths by opening the PixelMath window and putting B in the R/K box, B*.5+R*.5 in the G box, and R in the B box, then check Generate Output, Create New Image, and select RGB in the Color Space drop down menu to get a nice colored image. I applied the PixelMath and obtained a new image. After applying STF, what I saw was a grey image with the same features as the two sources. I played with the SFT, HistogramTransformation, and HistogramEqualization, but could get nothing sensible. Did the video omit a step? Maybe someone else can take it from here. Gerald, are you monitoring?
Since writing the above, I found a forum thread in which JC, I think, said it was necessary to stretch the images before combining them. I tried stretching before applying PixelMath and eventually obtained an image of sepia tone. With further prodding using ColorCalibration and the HistogramTransformation, I was seeing differentiated colors, garish greens and reds or purples. They added up to nothing resembling a visually pleasing image, but perhaps it is progress.
Third try. I don't know how to quantify the effects of multiple HistogramTransformation applications, but I tried to stretch both the source images about the same amount. Then I applied the PixelMath and equalized the colors using the HistogramTransformation separately in R, G, and B. CurvesTransformation set at RGB/K lightened it up. The result is the second attachment.
I see that ESA and NASA also distribute a free-standing version of FITS Liberator that works on both PCs and Macs. It may or may not make some things easier. I have yet to try it. There is a tutorial at
http://hubblesite.org/get_involved/hubble_image_processors/visualizing_hubble_data.pdfPerhaps there is a good tutorial for doing this in PixInsight that I am unaware of. I can think of nothing that is more likely to boost the popularity of PI. There must be hundreds of thousands of people who don't own astrophotography gear yet would like to develop their own Hubble images.
Gary
