Processing HDR images
Introduction
An HDR image generated from differently exposed photos can not be viewed properly on standard monitors or on prints. This is because this "raw" HDR image contains a range of values from the deepest shadows to the brightest highlights that exceeds the reproducing capacity of low dynamic range media such as standard monitors.
This is why it is necessary to process the HDR image, mapping its tonal values so that they fit in the limited tonal range of display and printing devices. This way, the details in highlights and shadows stored in the 32-bit HDR image will then become apparent on 8-bit displays. This process is also known as Tone Mapping.
Photomatix Pro provides two methods for tone mapping an HDR image in order to reveal its details in highlights and shadows. One method is called "Details Enhancer", the other "Tone Compressor". The settings detailled below relate to "Details Enhancer".
The HDR processing workflow is as follows:
1. | Generate an HDR image, or open a saved HDR image.
2. | On the HDR menu, click the Tone Mapping item.
To process HDR Tone Mapping as an automated process, please refer to the section Batch Processing.
To use Details Enhancer with large files, click on Large File Processing from menu HDR. This function allows you to view a preview of the result (extracted from a low resolution of the image read from disk) and then to run Details Enhancer on the whole image file. The function only works with HDR images in Radiance RGBE format (.hdr).
Tone Mapping settings
Strength
Controls the strength of contrast enhancements. A value of 100 gives the maximum increase in both local and global contrast.
Color Saturation
Controls the saturation of the RGB color channels. The greater the saturation, the more intense the color. The value affects each color channel equally.
Light Smoothing
Controls smoothing of light variations throughout the image. A higher value tends to reduce halos and give a more natural look to the resulting image. A lower value tends to increase sharpness.
Luminosity
Controls the compression of the tonal range, which has the effect of adjusting the global luminosity level. Moving the slider to the right has the effect of boosting shadow details and brightening the image. Moving it to the left gives a more natural look to the resulting image.
Microcontrast
Sets the level of accentuation of local details. The default value (2) is often the optimal one.
Micro-smoothing
Smoothes out local details enhancement. This has the effect of reducing noise in the sky for instance and tends to give a "cleaner" look to the resulting image.
White Clip - Black Clip
Both sliders control how the minimum and maximum values of the output image are set. Moving the sliders to the right increases global contrast. Moving them to the left reduces the clipping at the extremes. The White Clip slider sets the value for the maximum (pure white or level 255). The Black Clip slider sets the value for the minimum (pure black or level 0).
Gamma
Adjusts the mid-tone of the tone mapped image, brightening or darkening the image globally.
General options
Bit-depth of output image
Sets the bit depth (number of bits per color channel) of the resulting image. Choosing 8-bit compresses the dynamic range down to an 24-bit RGB image that can be saved as a JPEG or 8-bit TIFF file. Choosing 16-bit compresses the dynamic range down to a 48-bit RGB image that can be saved as a 16-bit TIFF file.
The default value is set to 8-bit. You can change the default in the Preferences panel under the Photomatix menu.
360º image
This option is only applicable in the case of Detail Enhancer. It needs to be checked when the image processed is an equirectangular image intended to be viewed as a 360º panorama. Given that Details Enhancer takes into account local contrast, the 360º seams of an equirectangular image will be assigned different tonal values, which will result in a visible seam once the resulting image is rendered in a panorama viewer. Checking this option will correct for this.
This option should only be checked for equirectangular 360º images. Checking it in other cases may produce less optimal results.
Note: Checking this option increases the amount of memory necessary to process the image by about 50%. Processing times will also be increased.

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