AstroBKK
Trifid Nebulae treatment with StarTools
Frames acquired as per procedure described here, with a Celestron 9.25", focal ratio 10, ASI294 MC Pro OSC camera, bin 2, cooled 0deg.C, 10*300sec, guided. Sampling 1.43"/pix. Stacked in DSS with darks and flats.
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Before starting, check screen settings, especially gamma and brightness, too low values may lead to uneven background when displaying image on other screens. Perform treatment under same room lighting.
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Bin: if minimum details such as faint stars spans over several pixels, binning should be applied. Beside noise reduction, this will reduce picture size and accelerate calculation time. Care must be exercised not to bin too much as it may however limit deconvolution as some information may be lost.
Crop: edges must be removed to remove captor border artifacts and highly vignetted areas. If wipe still yields halos or gradients in the background, a wise crop area selection may help. It is also used to center or reframe object if needed.
Wipe: test both gradient and vignetting buttons, to get the most homogeneous background in the stretched image. Mask may be necessary to suppress artifacts if need be. A sweet spot can also be found with the point with drop-off point slider, and increase dark anomaly slider if needed.
After wiping
Autodev: select area to get good compromise between background noise and object visibility (especially for it's faintest areas). The 2 sliders outside roll influence and more importantly shadow uniformity are very useful to reduce background noise. Ignoring fine details can further clear the background without impacting the object significantly. The gamma slider will increase noise but help to avoid ugly background issue when picture is displayed on others screens, so it can be used to pre-compensate settings on these others screens and ensure optimal view.
Deconvolution: select a sub-area to speed-up rendition (the upper part of the picture show results pre-view, lower part is original picture) Increase radius to reveal details, trying to find good balance between details and noise, and avoiding over-processed aspect. Stars must be monitored carefully, as rings may appear. A too low mask fuzz will lead to immediate stars background visibly different from reminder (boxes), while with too high fuzz, star'e edge artifacts will appear.
Life: buttons less=more or isolate usually gives the best results to improve background homogeneity, with proper strength to adjust effect intensity. Moderate & heavy buttons distribute colors in the object with little or no effect on background. The selection of power of inverse as compositing algorithm increases brightness without brightening that much the background.
Color: calibration can be done by selecting a white star (If color changed a lot once entering in the module, testing different LRGB emulation methods helps to get a natural rendition similar to before entering the module). Then adjusting color bias to eliminate green and balance others colors, closely monitoring stars. Cap green should be used before green bias reduction for objects without real green shades (unlike Orion). Star ringing issue usually occur at that stage of the treatment, and can be managed after noise reduction.
Denoise: adjust slider to remove clumps. In the second part of the module, increase grain dispersion to get a grain and clumps free image, especially on diffuse nebulous areas. Scales 1-5 can be used to keep details while optimizing noise, and proven very useful for galaxies. Reduce color details to keep small colored areas such as granulation in spiral galaxies. Adjust smoothness slides to remove the last remaining grain.
After noise reduction
Shrink: a simple tool aiming at reducing size of aberrant size. The shape of the selection in mask is very important (exclude very close stars).
Final Image
