A nice and easy way to re-introduce some global contrast, which IMHO generates visually pleasing results, is to apply a filmic tone-mapping curve to the result. The algorithm typically produces a flat and dull result, but with preserved local contrast. finally, the new log-luminance channel is converted back to linear encoding, and blended into the initial RGB channel.the high-frequency part is added back to the blurred and scaled log-luminance.a linear scaling is applied to the blurred log-luminance.the high-frequency component is extracted as the difference between the original and blurred log-luminance values.the log-luminance is blurred with a bilateral blur operator.the input RGB image (assumed to be in linear encoding) is converted to log-luminance.The algorithm used in PhotoFlow is based on this work by Paris and Durand, and can be summarised as follows: This is not meant as a “battle” between the two programs, but instead as a way to discern the pros and cons of the two approaches, and see if we can get the best out of the two. Since the two programs use a quite different approach, I thought it would be interesting to compare side-by-side the results on the same image. Recently there has been quite some work done both in RawTherapee (mostly by and PhotoFlow, to improve the visual quality of shadows/highlights compression. This is usually achieved through various forms of edge-aware blur operators. Shadows and highlights have to be separately processed without creating visible and unpleasant halos. However, it is a tool in which the actual algorithm being used plays a crucial role one the quality of the result. Used with moderation, it can rescue images for which the dynamic range is too big to be properly displayed. The value of the Radius slider influences the effective area of the Shadows and Highlights sliders.Shadows/highlight compression is one of the fundamental tools in image processing. The higher the tonal width value, the more tones are affected. Though the underlying math is a bit more complicated, think of a histogram - the highlights tonal width specifies the range of tones from the white end of the histogram which the highlights slider will affect, and the shadows tonal width specifies the range of tones from the black end of the histogram which the shadows slider will affect. Shadows/Highlights Tonal Width allows you to control how bright an area must be for it to be affected by the highlights slider, and how dark an area must be for it to be affected by the shadows slider. However, in some cases working in RGB space may oversaturate the shadows, in which case you should switch to L*a*b* space.Īllows you to brighten the darkest parts of the imageĪllows you to darken the brightest parts of the image. If the photographed scene has a high dynamic range (very deep shadows and very bright highlights) then use the Dynamic Range Compression tool to compress the dynamic range to a more manageable level, and then optionally use this Shadows/Highlights tool on top of that.Īdjusting shadows and highlights in the RGB space preserves image saturation which usually looks more natural than working in L*a*b* space which tends to desaturate affected areas. Use it in moderation to preserve a natural look. This tool has received a new engine in RawTherapee 5.5, it now uses an edge-aware fast guided filter to prevent halos and operates by default in RGB space to preserve saturation. Use this tool to brighten the shadows or darken the highlights of an image.
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