The Adaptive Contrast Curve .8bf Plugin
Version 1.112, updated 12/6/2015


Adaptive Contrast Curve samples the pixels in separate regions of the image and applies a contrast curve centered on the local average.  It operates similarly to the Adaptive Histogram EQ filter, but uses an S-curve instead of histogram equalization.  It is the kind of effect that one associates with forensic “digital enhancement,” and may be used photographically to bring out texture or even create an embossed look.  It is not often the best for general image enhancement and is very subject to artifact.  It is often best to apply the filter to a selection of the image to minimize artifact.

• The long dimension of the image is divided into the number of sections specified by the Regions control, and the rest of the image sectioned off accordingly.  Each region is processed individually; more regions require more processing time.  Move the Regions slider to the top, then click the adjacent spin button to increase the maximum number of regions to 1/2 the long pixel dimension.
• The Amount setting controls the steepness of the contrast curve.  Unlink the amounts to adjust the high and low ends of the curve independently.

• In Normal mode, the plugin processes each RGB channel separately.  The processed colors often have an unreal appearance but may still be interesting.  Color controls how much of the processed color components are included in the final image.  In Grayscale Only mode, the plugin processes a grayscale copy of the image, then combines it with the color components of the original image.  This is similar, but not identical, to Normal mode with Color set to zero; sometimes the results of the latter are superior.  However, the former runs faster.  In Color Only mode, only the processed color components are used in the final image.
• Vibrance preferentially increases the saturation of less-saturated areas of the image.
• Level moves the inflection point of the contrast curve up or down.  It helps to unlink the amounts if the inflection point is moved.
• Especially with a high number of regions, note that Mean runs faster than Median.

• Dark/Light Mixer works as follows:  the central position (zero) displays the processed image; the far left is like Darken blend mode, and the far right is like Lighten.
• Use the masks to protect blown shadows and highlights.  Try starting with Tonal Width and Radius 0 and Amount 100.  Raise the Tonal Width and Radius to create an appropriate mask, then reduce Amount to 0 and gradually raise it again to achieve the desired effect.  Amounts greater than 100 only affect blurred areas of the mask.
• The white histogram (background) is the original image; the black one (foreground) is the processed image.

The plugin works with 8- or 16-bit RGB and grayscale images.

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Download the zipped file, then copy AdaptiveContrastCurve.8bf into your plugins folder.  It will appear under “RC Filters.” version 1.112, 299 KB, 64-bit applications.  It works for me in Photoshop CS5 and PhotoLine 19.5, Windows 7. version 1.112, 294 KB, 32-bit applications, Windows 32 or 64 bit.  It works for me in IrfanView 4, Windows 7. |  source code version 1.112.1, 186 KB, “retro” 32-bit version compatible with Windows XP.

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© 2015 by Russell Cottrell; released under the GNU General Public License.
Updated 12/6/2015.