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Photoshop plug-ins for retouching
Dynamic range compressor

Quick introduction

This plug-in lets you achieve HDR like results from a single image. Unlike HDR technology that uses several images, our technology does not create ghost halos around objects. This is the Dynamic Range Compressor’s control panel. Click on the image for a larger view. It works with the following image modes: 8 & 16 bit/channel: RGB, CMYK, Grayscale, Duotone, Lab.

What is HDR - High Dynamic Range - and why is Low Dynamic Range

a problem?

Dynamic range is the span from the darkest value to the brightest value. Now this sounds simple enough - but the sensors of the eye and the camera and the scanner are not equal. This means details in darks and lights are not registered equally by the eye, camera and scanner. The problem is that the camera or scanner is not as sensitive to the entire dynamic range as the human vision is. In a scene where the eye will perceive details in both the light and dark areas at the same time, the camera or scanner will only be able to capture one end while rendering the other as an underexposed or overexposed mass. Below is a classic example of this: The shadow area is underexposed while the lights are over exposed.

Shadow illumination

Compressing shadows can of course be used for shadow illumination. The following image shows how much information actually resides in underexposed areas. But you should be aware that any noise in the darks (and there is often much) will be also be enhanced.
Original

The controls

First group lets you compress either shadows or lights. Shadow compression is also called shadow illumination. Compression Factor boosts the effect of the compression. Offset will add (or subtract) a given value from every pixel of the image, thus brightening or darkening the impression, but not changing the dynamic range by compression or expansion. Black Point will stretch the dynamic range down towards black, leaving the highlights as they are, but progressively deepening the darker colors. Turn on Black Alert, or watch the histogram, when using this slider, so you don't overkill the darkest areas. Shadow Depth does the same in principle, but it leaves everything brighter than Shadow Threshold alone. Thus you can specify the threshold from where you will expand the dark range to the black point. The last group lets you adjust saturation and also adjust the effect by mixing more or less with the original.

Graduated effect

These controls are common for many of the Power Retouch plug-ins. Using graduated effect will cause the filter to apply it's filtering at full strength in one side of the image and then fade the effect out towards the other side. You can change direction by right clicking the preview. Midpoint will shift the balance between how large an area will be filtered at full strength and how much will have a faded out effect. Contrast will change the acceleration and spread of the fade-out.
In this example we applied a graduated effect towards the bottom, setting midpoint to the edge of the gray clouds. This retouch brought light into the underexposed foreground, bringing it forward, without altering the sunset.
In this example we also used graduated effect, filtering the bottom only in order not to alter the landscape or the high contrast of the bransches against the sky.