RGB TIFF from Zwo FIT

gtg

With apologies for duplication, I am re-posting part of a query from a thread under a different header; this header may be more suitable at this stage. As background: I'm using Zwo Asiair, version 4 FITS Liberator, Canon EOS camera (OSC).

... Continue to be perplexed about Fits Liberator. Have downloaded OSC FITS example files of unknown origin (probably NOT Zwo software) which open in FL; in these cases, FL shows 3 planes (RBG) in the pull down option. (None of which display with the 'checkerboard' pattern as might be expected.) This is not the case when I open my Zwo FIT files - FL shows only "Image 1, Plane 1". [Image overlain with a checkerboard pattern - assumption this has to do with Bayer patterning.] If I save from FL as a TIFF I get only a grayscale image. In response to comment concerning FITS header - yes, "BAYERPAT" = RGGB in the Zwo-generated files. So I should see 3 "planes" = channels, no? And, yes, a Windows operating environment. My overall goal is simply to generate a single RGB 16 bit TIFF from a Zwo FIT file, so I can set the FL issue aside if someone can give me precise directions for doing that using freeware. ... Thanks to all for help.

johnpd

Download and install ZWO ASISTUDIO. It is free and has a FITS viewer app from which you can save a Fits file to a Tiff.

JohnD

gtg

Thanks but ..... I do have Studio which does open Zwo FIT files in color and allows save to TIFF. However, when the TIFF (or original FIT) file is opened in e.g. GIMP or Deep Sky Stacker, it's presented in grayscale. If I look at the histogram in GIMP, I can see 3 peaks which likely correspond to the RBG channels combined in what GIMP calls "Value" = luminance. GIMP (or DSS) cannot directly resolve the RGB channels (using either the original FIT or derived TIFF). That's basically why I tried using Fits LIberator - "it is writen" that FL will open FITS file RGB channels ("planes") separately. These can be saved in grayscale then independently opened as RGB channels in an image processor like GIMP. I can do this with downloaded FITS files but not with the Zwo FIT files (which is why I started this inquiry under a query whether a Zwo "FIT" is the same as the rest of the world's "FITS" file). To be more precise, then, I'd like to convert a Zwo FIT to an RGB TIFF with separate channels that can be manipulated in GIMP or DSS. Make sense? Thanks.

johnpd

It is much easier if you try Affinity Photo. No need to play with individual channels, but you can if you want. They have a free trial and it only costs $55 if you decide to buy. No subscription is needed as with Adobe products.

It will open the .FIT(s) file directly. The image might have a green cast to it, but don't worry that will be quickly removed.
Do any necessary cropping.
Do "Layer" > "Merge Visible" (It automatically creates a Levels and a Curves adjustment layer when the FIT(s) file is opened. To do the next step requires combining all layers.)
Do "Filters" > "Astrophotography" > "Remove Background".
--a. Move the double white circle generated in the middle of the image to an area of the image that has little data.
--b. Click the little box next to "Sample at handle position".
--c. The background should immediately darken and any color cast should be eliminated.
--d. You can adjust the black level if need be by moving the slider at the bottom. (You could adjust the Gray/Red/Green/Blue levels then as well, but I find those are generated good and any color adjustments can be done with "Color Balance" or you could do adjustments to individual channels by selecting the "Channel" at the top.
--e. Click "Apply" when satisfied.
Then do a series of "Curves" and very minor "Brightness/Contrast" adjustments (it does not like doing consecutive "Curve" adjustments). Doing "Levels" adjustments would be difficult as the black level is pretty well shifted to the left at this point, although "Curves" can start shifting it right.
Do any "Color Balance" adjustments.
If the free trial allows you to save the resulting image, select 'File" > "Export" then the particular format you want to save the image in and you are good to go. [NOTE: for some reason it does not default to saving it to the same folder as the .FIT file. You need to select the folder you want.]
After that I like to use Topaz DeNoise to get rid of any image noise.

JohnD