Jan Esmann and Power Retouch. All rights reserved.

Photoshop plug-ins for retouching

Histogram repair

Quick introduction

This Histogram Repair Photoshop plug-in interpolates the missing values in a posterized histogram. This Photoshop plug-in does not have a
control panel.
It works with the following image modes: 8 & 16 bit/channel: RGB, CMYK, Grayscale, Duotone, Lab.

Video introducing the Histogram Repair Photoshop plug-in

We developed means to avoid posterization during image-editing with the other Power Retouch Photoshop plug-ins. Once that principle was in place it was natural to release an individual plug-in that did something similar as a repair of the damage that might be created by editing images with other means than Power Retouch. It is of course best to avoid posterization within the image-editing algorithms, rather than to fix posterization after the editing has created it. So this plug-in is actually not intended to be used in conjunction with Power Retouch, because most Power Retouch plug-ins have anti-posterization built-in as an option. It is provided as a possibility to fix damage that other software has done. Also the Histogram Repair plug-in provides a means to turn an 8 bit image converted to 16 bit, into a true 16 bit image (more about this below). Posterization is usually not visible since it in most cases only spans a single value. But further editing of a posterized image can widen the posterization gaps so much that the image appears as if divided into bands. When repairing an image where the posterization gaps are only a single value wide, you will not be able to see any difference, and this is how it should be.

After adjusting levels

Here is an underexposed photo and its histogram.
Once we adjust levels in Photoshop we get a heavily posterized histogram.
After running Histogram Repair we get this histogram.

Converting 8 to 16 bits

Here is an 8 bit image and its histogram
After converting the 8 bit image to 16 bits you get a heavily posterised histogram
After running Histogram Repair the missing values have been interpolated.