[Digikam-devel] [Bug 163286] New: Accurate histogram preview required

Dik Takken d.h.j.takken at xs4all.nl
Thu Jun 5 17:28:19 BST 2008

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           Summary: Accurate histogram preview required
           Product: digikamimageplugins
           Version: unspecified
          Platform: unspecified
        OS/Version: Linux
            Status: NEW
          Severity: wishlist
          Priority: NOR
         Component: Adjust Curves
        AssignedTo: digikam-devel kde org
        ReportedBy: d.h.j.takken xs4all nl

Version:           0.9.4-beta4 (using KDE 3.5.8)
OS:                Linux

I get the impression that the histogram preview is calculated from a downscaled version of the image. The result is that the histogram preview is not very accurate.

When working with large images, this causes problems. The original image may contain many small highlights that completely disappear when the image is scaled down. So, in the Adjust Curves preview window, these highlights go unnoticed. When adjusting the curve, you can easily clip the high lights without noticing it. Only after applying the final Adjust Curves settings, the full histogram is re-calculated. Often, it turns out that the histogram has been clipped, while the preview looked just fine.

IMHO an accurate preview of the resulting histogram is critical to a Adjust Curves tool. Maybe the plugin should have an option to create a preview based on the full image in stead of a scaled down version. I can imagine adding a 'fast preview' checkbox that is checked by default.

The Adjust Levels tool will probably have the same problem, but I did not check.

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