Initial draft for high quality processing button, fron Jens.

content/darkroom/darkroom-view-layout.md

@@ -73,6 +73,9 @@ From left to right:
 ![color-assessment-icon](./darkroom-view-layout/color-assessment-icon.png#icon) [color assessment](../module-reference/utility-modules/darkroom/color-assessment.md)
 : Toggle the ISO12646 color assessment view.
 
+![high-quality-processing-icon](./darkroom-view-layout/high-quality-processing-icon.png#icon) [high quality processing](../module-reference/utility-modules/darkroom/high-quality-processing.md)
+: Toggle high quality processing mode.
+
 ![raw-overexposed-icon](./darkroom-view-layout/raw-overexposed-icon.png#icon) [raw overexposed warning](../module-reference/utility-modules/darkroom/raw-overexposed.md)
 : Toggle raw overexposed indicators (right-click for options).
 

content/module-reference/utility-modules/darkroom/high-quality-processing.md

@@ -0,0 +1,29 @@
+---
+title: high quality processing
+id: hq-processing
+applicable-version: 4.8
+tags:
+view: darkroom
+---
+
+Click the ![high quality processing icon](./high-quality-processing/high-quality-processing-icon.png#icon) icon to activate high quality processing in the pixelpipe.
+
+Darktable pixelpipes process the modules in slightly different ways, the thumbnail pipe as an example is optimized for speed.
+
+The darkroom pixelpipes for the main canvas and the second monitor try to keep resources within limits by downscaling and by
+restricting the processed data to what is actually displayed - in darktable speak this is the "region of interest" (ROI).
+
+Yet - for exports we have to process the whole image - likely without downscaling - resulting in much larger processing times
+and possibly visible differences compared to what you have seen in darkroom.
+
+These differences are mostly very subtle but in some cases they are likely to be observed.
+Modules like "diffuse or sharpen" using large radii, "profiled denoise" or "local contrast" are more prone to this problem.
+
+For the user this usually means: there will be visible and unexpected differences between "what you see in darkroom" and the exported image.
+Also there might be visible differences if you zoom in or out.
+
+To avoid these problems you might activate the high quality processing mode. If toggled on, the darkroom pixelpipes are processed
+with all available data so the results are as while exporting in high quality mode.
+
+Please note, this takes large resources and requires a good OpenCL card and CPU for a responsive user interface especially if you keep changing
+any module parameters.