Pixiq

So, we have all these sliders with many combinations; where do we begin? Are there “best” workflow techniques for achieving a realistic versus a surreal HDR look? Yes, there are, but watch out for the pitfalls that can make your image look like it was processed by an HDR amateur. One lesson you will quickly learn is that some settings will work well for one image but not another. That’s why tone mapping using batch processing should be avoided.

Step 1: Set Gamma – Begin your work by setting the Gamma slider so midtones fall close to the middle of the histogram. Photomatix Pro is very good at determining brightness, so it usually won’t be more than a slight move to the left or right.

Step 2: Set Strength and Light Smoothing – These two sliders should be used together and are the essential tools for controlling local tonal variations. For your image to look like a traditional photograph, move the Strength slider to the left in the range of 25 – 50 and Light Smoothing to High or Very High. For a surreal HDR look, try Strength levels from 50 – 100 and move Light Smoothing to Medium.

Most of my images are tone mapped with Strength levels in the 50 – 100 range and Light Smoothing at Medium or High. I rarely use Light Smoothing at Low, and never at Very Low. For the Beach Huts scene, I wanted a surreal look for the clouds so I used a higher Strength setting of 92. I kept the Light Smoothing set to Very High to maintain traditional tonal relationships.

Step 3: Set White Point and Black Point – White Point and Black Point on the Tone tab are used to add global contrast to the image by clipping pixels to pure white or pure black. Keep in mind that these sliders also change the midtone brightness. I always try several positions for each slider, and have found that White Point and Black Point set full right at 5.00% each will create a surreal HDR effect. Most of my images end up with the two points set about half way in the range. You may elect to preserve all pixels by keeping both set to zero and apply clipping later using a general image-processing program. In the Beach Huts image, the White and Black Points are set low to limit the contrast in the sky and keep the scene looking believable.

Step 4: Set Microcontrast and Micro-Smoothing – Use Microcontrast and Micro-smoothing on the Micro tab to impact the local contrast enhancements. To create an image that has maximum small-scale contrast, raise the Microcontrast to 10 (right) and lower the Micro-smoothing (left). For an image with softer transitions in local contrast, lower Microcontrast to –10 and raise Micro-smooth-ingto30. Avoid moving both sliders full right or full left, as they tend to cancel each other out.

Let’s say that you want the pine needles on a tree or the intricate details of fine artwork to stand out and be sharp; in such cases, raise the Microcontrast to be somewhere in the range of 0 – 10 and lower the Micro-smoothing to 0. On the other hand, if you feel that the fine details in the scene detract from the look you’re trying to achieve, such as in a city scene at night or a beach scene at sunset, then lower the Microcontrast and raise the Micro-smoothing.

Most of time, I keep Microcontrast in the range of 0 – 7 and Micro-smoothing between 0 – 10. This produces images that are not over-the-top in local contrast, graininess is controlled, and the overall look is pleasing. Images that include sky are prone to grain, so consider setting Micro-smoothing between 2 – 10 and Microcontrast anywhere from 0 to –5. The Beach Huts scene has Micro-smoothing set at 2, but if a print of the image showed grain, I would increase Mico-smooth-ing to between 3 – 5 and try again.

Grain vs. Noise in HDR Tone Mapping

Grain is caused by excessive local compression in the tone mapping process. It can obliterate details, just like noise, but details are recoverable by lowering compression. On the other hand, details lost due to noise cannot be recovered.

Note: During Microcontrast and Microsmoothing adjustments, take advantage of the 100% preview crop by clicking on the image. Simply make your adjustments in full view then click on an area in the image and a 100% preview crop of the area will be displayed. It is best to choose an object that extends into the blue sky rather than just the blue sky.

Minimizing Halos: A halo is fringe of brightness around an object that extends into a region of uniform tonality. A building that extends into a blue sky is a good example of where halos often develop. The blue sky in the Castle scene  was particularly problematic where the sky meets a dark roofline of the building. The Highlights Smoothing slider on the Shadows and Highlights tab is very useful for controlling the halos created around objects surrounded by blue sky. The use of this slider will allow you to raise Strength and lower Light Smoothing for a more surreal HDR image without the halos.

If you are dealing with halos in cloudy skies rather than blue ones, however, the Highlights Smoothing slider will not work very well. The clouds don’t always fall into the highlights tonal range, so smoothing is inconsistent. Unlike blue skies, images that have cloudy skies are much more tolerant of higher Strength and lower Light Smoothing values. In the image of the Portland Head Light in Maine, you can see that the blue sky with clouds disrupts the creation of strong halos even though I have the Strength set at 100 and the Light Smoothing at 0.

Tone Reversals: Tone reversals are the result of taking regions of an image that we normally perceive as brighter than other areas and making them darker. When an image includes the sky, it becomes easy to identify a tone reversal because our visual perception that the sky is the brightest part of the scene is a strong one. The Strength and Light Smoothing settings strongly control tone reversals. Raise the Strength and lower the Light Smoothing to create tone reversal; lower the Strength and raise the Light Smoothing, and the tone reversal is corrected.

Tone reversals are more forgiving when the scene does not include sky; it is possible to push the envelope much further before problems appear. When we don’t have a familiar visual reference like the sky, we are more accepting of the visual effects of higher Strength and lower Light Smoothing. Compare the settings of the Porch image (bottom right) with those of the Castle image.

White Surfaces: When HDR images are tone mapped, it is common for white areas to be rendered gray. The Highlights Smoothing slider on the Shadows and Highlights tab is the tool for turning the gray areas back to white. I typically set the white color to a very high-key gray and then apply a Levels adjustment later in an all-purpose image-processing program.

Noise in the Shadows: To correct camera noise in the shadows, try to desaturate the shadow area by using the Saturation Shadows slider on the Color tab. This will help with color noise. You can also raise the Black Point and follow with Shadows Clipping on the Shadows and Highlights tab to create black areas in the shadow regions and, in effect, lower the visibility of the noise.

Controlling Grain Enhancements: Grain commonly appears in skies and is most evident when you zoom in closer than 100%. If your image has high grain due to image compression, you can try these slider adjustments to mitigate the problem. Remember to adjust the slider when viewing the full image then zoom in to 100% to see the results:

• Lower the Strength values

• Raise Light Smoothing to High or Very High

• Lower Luminosity

• Raise Highlights Smoothing

• Raise Micro-smoothing

Here is a strongly tone mapped image of the Lincoln Memorial, the Monument and the Capitol Building (above). The buildings look nice, but the sky is full of grain.

The easy solution would be to lower the Strength, but if we look at the other settings, it becomes apparent that there are a few other adjustments that can be made to help the situation. Notice the positions of the Luminosity and Gamma sliders. As the Luminosity slider moves to the right, it increases brightness and micro-compression. The Gamma slider also increases brightness as it moves to the right. In this case, if we want to reduce compression, the sliders positions need to be reversed.

When I move the Luminosity slider to the left, it lowers the micro-compression but also darkens the image, so I counter the darkness by moving the Gamma slider to the right. Notice the position of both sliders in the second image (above), where grain is substantially reduced. The Micro-smoothing slider (not shown—located on the program’s Micro tab) was moved from 0 to 4 to further reduce grain. The image now shows an overall improvement in grain reduction, but will still need some Levels and Curves adjustments later in post-processing.

The important point here is to know that the Luminosity, Microcontrast, Micro-smoothing, and Gamma sliders can all be used to fine-tune the brightness and smoothing of the image. They are interrelated and when one is moved, another can be adjusted to maintain harmony in the image.