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+--- Thread: High dynamic range (/Thread-High-dynamic-range)
High dynamic range - fjcaba - 01-24-2022
Hello,
My hobby is astrophotography and what I cannot do with Siril in linear image or in PixInsight LE in non-linear image I do it with GIMP.
I would like to ask you a question regarding several closely related processes.
I work with raw format that I convert to TIF. In photographs with a high dynamic range, and assuming there has been no loss of information in lights and shadows, it is necessary to increase light in shadows and reduce light in highlights, and then increase local contrast. In GIMP with the G'MIC plug-in I find several processes that I can use. If I use masks I can use them on certain areas and if I break up the image with wavelets
I will be able to use them only on certain structures (stars or nebula).
In relation to the dynamic range of the image:
1. Colors > Exposure (exposure for me is a combination of aperture, ISO and exposure time, but this process has two sliders for shadow level and 'exposure'). There is a tutorial to bring up the shadows, but what about the highlights?
2. Colors > Shadows/highlights
3. Colors > Brightness/contrast
4. Colors > Auto > Equalize
My doubt with these is because I think that they are several perspectives of the same thing: the modification of the black point, the white point, and the midtones in the histogram; and I have no information on whether they cut out the information or not. Is there any other tool that will help improve the dynamic range of this
type of images?
Regarding the dynamic range, and trying to be clearer, I am looking for a tool that allows me to increase the space of the shadows and the highlights, at the expense of a compression of the midtones, so that I can extract detail from the extremes of hystogram (and this is not only to move three points in the hystogram I suppose)
And to increase the local contrast:
1. Filters > G'MIC > Details > Local contrast enhancement
2. Filters > G'MIC > Details > Tone mapping
Are they the same? From a technical point of view, could someone tell me what each of these processes does?
RE: High dynamic range - Ofnuts - 01-25-2022
I would ask in an astrophotography forum. Most things you'll find otherwise (tutorials... or script/filters) assume a "usual" image, with information across the whole range, while astrophotography pictures are quite different.
RE: High dynamic range - fjcaba - 01-25-2022
(01-25-2022, 12:28 PM)Ofnuts Wrote: I would ask in an astrophotography forum. Most things you'll find otherwise (tutorials... or script/filters) assume a "usual" image, with information across the whole range, while astrophotography pictures are quite different.
Yes, I know it. I know what I want to do with the image. But my question is related to knowing how those processes work, if they cut information or not, the mathematics on the pixels, ... I can't find information about each process in the web.