Clipped Pixels Mapping/warning with Mask

[tomczak]

Mapping clipped pixels has been discussed here:

http://www.dl-c.com/discus/messages/2/12564.html
http://www.dl-c.com/board/viewtopic.php ... ning#p3274

I find mapping pixels that are at or near 100% in HSV-V and HSL-L most useful: the first one will show pixels blown in at least one of RGB channels, the second in all three (i.e. pure white).

To map, open Mask tool, then Colour Range. Select full H and S ranges (i.e. all white) and leave V (or L) at 100%. Apply.

You can also open Readout Tool and Histogram Tool simultaneously, and probe the image. Also, instead of opening Histogram, a Brightness Curve transformation can be opened - this, unlike Histogram, can show probed values on the histogram.

Note that this method can't be used on Preview to predict what areas will be clipped as a result of a transformation settings. It can be used on the output image resulting from the transformation though.

[tomczak]

Similar clipping/maxout warning system works in RAW dialog preview, as follows:

1) in RAW dialog, in Options, check 'Show Clipped Pixels'
2) also in Options, choose either HSV (default) or HSL Colour Space: the first one will show clipping in at least one RGB channel, the second in all three (pure white)
3) the predicted clipping map will be shown only if the Dynamic Range white slider (in Gray tab) is moved slightly beyond 100% (e.g. 100.8%); this needs to be done even if clipping is unrelated to the Dynamic Range adjustments.

Note: blocked (fully black pixels) can be similarly mapped by moving the black slider in Gray/Dynamic Range beyond 0% (i.e. slightly negative value). Choosing HSV/HSL makes little difference in this case.

Warning: since Show Clipped Pixels reverses the pixel colour (i.e. blown pixels become black, blocked pixels become white), and this is used in the updated RAW preview histograms, the histograms are invalid at this point. Uncheck 'Show Clipped Pixels' or move Dynamic Range slider to within 0-100% to see the proper preview histograms.

This technique is only applicable to the RAW dialog preview, not to the regular preview window.

[tomczak]

A quick way of mapping the maxed-out pixels in an image is to open Gray/Levels and Color, extend the white slider in Dynamic Range slightly beyond 100% (e.g. 100.4% - extending it further will include more near-saturated pixels), and check Invert Clipped pixels in preview. HSV will map pixels blown in at least one channel, HSL will show pure white.

[tomczak]

This may look like a strange setup, but I find it useful - often clipping is not easy to find with the histogram alone:

2013-07-04_084729.png (109.1 KiB) Viewed 5601 times

Windows from left, clockwise:
- Image window; clipped pixels shown in red.
- Mask Tool/Color Range: set to HSV, masking any value of H and S, but only V=100%. It maps pixels clipped in one or more RGB channels.
- Histogram Tool/HSV-V (to correspond with the Mask Tool warning map).
- Readout Tool: set to RGB.
- Magnifier.

Tips:
- If Magnifier window has focus, the readout tool will work simultaneously; the reverse is not true.
- HSV-V histogram (and the corresponding v=100% mask) shows the pixels maxed out in at least one RGB channel
- probing the mapped area with Readout tool in RGB shows which channel is blown (in the example above: G and nearly in R)

Note: This technique can only be used on image windows, not on Previews.