Hello Siril users and programmers, this is my first post here. Thanks to all, who made Siril such a strong software for stacking and processing.
In Siril there is only one autostretch option avialble. This is in many cases a too strong stretch preview, to judge the effect on operations on the linear image, like star color, denoise, deconvolution etc.
Is there a chance, to implement more grades of stretch? For example, in the GraXpert App I can choose from 10%, 15%, 20% and 30%. Heaving more options would help a lot, to see better the effects of denoising and sharpening.
The other options like “Logarithm”, “Square root” or “Square” I never used and don’t see any benefit in them. Does somebody uses them?
Besides Linear, I use the Square Root and the Histogram previews all the time. Square root allows you to reasonably see your linear data as linear off the screen without turning on Color Management (which has its own idiosyncrasies)—so I very often do stretch manipulations on linear data in that mode. Histogram preview is an extreme stretch that lets me see the extent of what’s in my data, so I use that for evaluating things like gradient or noise removal.
I occasionally use Logarithm as a stretch that better fits data with high brights (think the Homunculus Nebula), but since I have no way to apply it to the data, it’s not that useful other than a quick look. I treat asinh the same way, but I have not found a use case for it (in 4 years of using Siril).
Great topic. I completely agree that improving the preview workflow would be a massive quality-of-life upgrade for daily processing. Here are a few features I would absolutely love to see:
Quick Toggle Button: It would be fantastic to have a single, dedicated button to instantly toggle between Linear and Autostretch view, without having to open the dropdown menu every single time. It’s an action I perform constantly, and streamlining it would speed up the workflow significantly.
Autostretch Intensity Control: While the default autostretch works perfectly 90% of the time, having a slider or a few preset levels to adjust its intensity (more or less aggressive) would be incredibly useful for demanding targets.
Advanced Manual Display Controls: Ideally, I’d love a more granular way to manually tweak the display stretch. The current MIN/MAX sliders are a good starting point, but it would be amazing if we could zoom into those sliders for fine adjustments and, above all, if a Gamma adjustment slider could be added to the panel.
Hopefully, the developers might consider some UI tweaks in this area!
It’s hard for me to imagine a workflow where you have to switch back and forth between “linear” and “auto-stretch” regularly and often. In fact, for an image that hasn’t been stretched yet, the image appears black, so only the “auto-stretch” view is useful. Once it’s been stretched, the opposite is true: only the “linear” view is useful.
Currently in the dev version this is possible to play with the target median parameter.
You can change this value manually by editing it, which offers a great deal of flexibility.
As for the gamma adjustment, I am not in favor of adding it. In my opinion, it would be a niche feature with little relevance to astronomical image processing.
