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Photomatix HDR Tone Mapping Plug-in

The 32-bit HDR (High Dynamic Range) feature released as part of Photoshop CS2 has the potential to allow photographers improved access to the wide range of tonality present in nature, but the tools needed to map the resulting files into something that can be displayed in print or on a monitor remain somewhat primitive. While I expect this situation to improve in future releases of Photoshop, users don't need to wait for Adobe.

Photomatix is made by HDRSoft, a France-based company that was founded early in the decade. The first version of Photomatix was released in February of 2003 and they have continued to improve the product ever since. Once Adobe released Photoshop CS2, HDRSoft created a Photoshop plug-in version of their excellent tone-mapping function and it is this that we will look at this week. The exact features included in the plug-in have changed somewhat from release to release as new ones continue to be added. My review here is based on the current version 1.1.1.

Photoshop itself offers four methods of mapping high dynamic range images into 16-bit or 8-bit format: "Exposure and Gamma," "Highlight Compression," "Equalize Histogram," and "Local Adaptation." Only Local Adaptation offers a reasonable to degree of control over the conversion process. By contrast, the Photomatix plug-in is full of options you can tinker with. The values used by each tend to be highly image dependent, but I'll try to give you some guidelines here.

To access the plug-in, select it from the Filter menu as you would a regular plug-in. Once open, you can select the size of preview image you desire. If your monitor is big enough, go for the 1024 pixel sized preview so you can see what you are doing better. The "Show Original" button allows you to toggle between previewing the effects of the filter and seeing your original image. The controls themselves are lined up down the left-hand side of the window. As you hover your mouse over each, a small description of its function can be seen at the very bottom. The filter dialog also contains a histogram and buttons to allow you to save and reload your settings.

As its name implies Strength controls the overall strength of the contrast enhancement effect. The maximum setting of 100% will give you good results with some images but you may need to back it off for others to avoid harshness. Play with this setting to see what works for you. Somewhere between 70 — 100% is a good place to start.

Color Saturation allows you to adjust the saturation of colors in the image. While you can certainly adjust saturation here, I'd suggest doing so only in situations where you need to make extreme changes since Photoshop natively provides much better controls for this.

Light Smoothing controls how aggressively Photomatix will be in smoothing luminance variations within the image. Setting it too low will result in obvious halos around edges. Increasing it will give more natural results. +1 seems to work well for many images. Try zero or +2 if that doesn't work. For my work, I've found little use for negative values.

Luminosity controls how shadow detail is rendered. Increasing it will allow you to see greater detail in the shadows. Set it too low and the image may well turn completely black. Set it too high and the image will be way blown out. The best setting is quite dependent on image content. Keep an eye on the histogram while you adjust Luminosity.

Micro-contrast determines the degree to which details will be accentuated. The default value of +2 works well for many images but may make things look too contrasty for some. Negative values tend to result in a fairly flat appearance.

Micro-smoothing smoothes out the changes introduced by micro-contrast. Think of micro-contast as determining the amount of contrast change and micro-smoothing as controlling the radius of those changes. Setting this value too low will give an over-sharpened look to an image. Setting micro-smoothing too high will leave you with a fairly low-contrast rendition.

White Clipping and Black Clipping determine the minimum and maximum luminance values mapped. Setting Black Clipping too high will give you blocked up shadows while setting it too low may remove the shadows completely. Personally, I prefer at least some shadows in a landscape shot, but feel free to adjust this to your taste. White Clipping should work similarly for your white point, but I've found it doesn't offer nearly the range of adjustment as the Black Clipping slider does. Generally, I just leave this set to its maximum. Keep an eye on the histogram while adjusting both of these.

After clicking on "OK," the tone mapping will be applied and you will be returned to Photoshop itself. Interestingly, the bit depth of your image will not be changed so you can perform further edits on it, still in 32-bit mode. When you are ready, use the regular Image >> Mode >> 16 bits/Channel (or 8 bit) using the Exposure and Gamma option. Generally, you will want to leave the sliders at their defaults of Exposure 0.0 and Gamma 1.0.

The Photomatix Tone Mapping plug-in can also be used on 16-bit images as an alternative to Shadow/Highlight. Its strength though really is with 32-bit images since lower bit depth images simply don't contain enough source information to allow for very extensive adjustments.

As mentioned, HDR isn't new with Photoshop, but Adobe introduced it to a wider audience as part of CS2 in the spring of 2005. By doing so, they also brought forth a new creative outlet for numerous digital photographers. Some seem fascinated by the ability of extreme HDR tone compression to turn photographs into works of art. Others strive more to create more natural looking renditions of scenes previously impossible using traditional techniques. Whichever group you fall into or aspire to, I hope this article helps you get there.

The Photomatix HDR Tone Mapping plug-in

Date posted: October 15, 2006


Copyright © 2006 Bob Johnson, Earthbound Light - all rights reserved.
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