In this Generate HDR – Step Two panel, the only option I normally change is to enable alignment of the input images. As discussed previously in the CS2 example, this ensures that minor registration errors do not creep into the combined image due to any slight misalignment of the camera during the capture of the input sequence.

From the three options for camera response curve, I keep the recommended default selection, “Use standard response curve.” MultimediaPhoto recommends this since they feel modern digital camera sensors are close enough to linear in their luminance response that calibrating a curve for a specific camera is of little benefit. Furthermore, the Gamma 2.2 curve (the “standard” curve referred to by this setting) applied to the sRGB and Adobe RGB 1998 color spaces is well defined and does not introduce a need for calibration. Photomatix is unlike most HDR tools in this regard. Most of the others calculate a curve by default, and many of them require an explicit curve calibration step that creates a saved profile for the camera.

If you choose, you can calculate a response curve using the setting “Attempt to calculate response curve.” Or if you know the input images came from a linear RAW conversion, you can select “Use linear response curve.” If you calculate the curve, Photomatix does not permit you to save and recall it. It simply calculates the response from each image sequence you process; the results of this are likely to be variable depending on how many images are in the sequence and the exposure interval between them. Note: CS2 does not provide any options regarding response curve. It appears to calculate a response curve from each image sequence; like Photomatix it also does not permit saving the curve.

Upon clicking OK at this point, Photomatix will compute the HDR image. On my workstation this takes about 10 seconds, around half of which is spent on image alignment. When the HDR image is created, it is opened for viewing in the main window:

As with other applications that display an HDR image on normal hardware, the monitor does not have sufficient DR to render a complete view. With the image open in Photomatix, functions are available in HDRI>Adjust View to step the exposure up and down. This provides a similar ability to view the image as does the exposure slider in CS2. In addition, Photomatix provides a small full-resolution viewing window that can be enabled or disabled. As the mouse pointer is moved over the HDR image, the viewer shows a normalized view of the image data from a small area around the pointer. You can quickly check detail and luminance across the image without having to adjust the base exposure of the entire image.

Some DR statistics are available by selecting the HDRI>HDR Histogram menu item:

This window shows a histogram, the range of 32-bit luminance values, and a mapping of luminance values onto relative exposure values. The histogram shown for this example looks pretty comparable in distribution to the one seen in CS2, although it appears to have clipped the luminance range on the bottom and top ends where no image data exists. As you can see, this example has a DR of almost 1500:1, essentially all of which is available for use during tone mapping as the next steps will show.

This is a good time to save the HDR image in case you want to come back to it later. As with CS2, there are two principal formats: Radiance RGBE and Open-EXR. The default is Radiance RGBE. Saving in that format here, the resulting file size is about 18.8 MB. Saving as Open-EXR with ZIP compression produces a file about 13.8 MB in size. This file sizes are similar to those generated from CS2.

As noted before, even though both applications support the .hdr and .exr file formats, the way the applications encode the image data is not necessarily compatible. Thus it is best to use the same application to both encode and tone map the HDR image file rather than try to cross-process HDR files between applications. (An exception to this rule is the Photomatix tone mapping plug-in, which works on HDR images created by the CS2 Merge to HDR function.)

Photomatix Tone Mapping

Here is where the heavy lifting occurs with the Photomatix workflow. After the above steps, there is an HDR image open in the main window. I select the HDRI>Tone Mapping menu item and the following window appears:

At this point, in contrast to the CS2 approach, Photomatix provides just one function. However, this one function provides a lot of creative control. While controls may appear complex at first glance, the sliders and drop-down lists, in fact, make it very fast to iterate through the choices.

A preview of the tone mapped image is shown. For screen capture size reasons it is shown here at the minimum resolution of 512 pixels wide. Selection buttons at the lower left of the window enable widths of 768 and 1024 pixels. The preview dimension is always width; it does not adjust to the longest axis depending on whether the image is portrait or landscape.

There is no choice of arbitrary resolution or zoom ratio, such as zoom percentage or actual pixels. In part this is because the preview shown here is only an approximation of what the final tone mapped image will look like. The Photomatix developers may have felt that looking at actual pixels of a simulated view is of limited value. Once the image is generated, it can be examined at higher zoom levels, and if necessary the tone mapping can be revisited. However this cycle takes time and so flexible preview sizing is one feature that I wish was present in the Photomatix tone mapper. Even the 1024 pixel width (just added in release 2.2.3) is small to work with for large files such as stitched panoramas.

Fortunately the other tone mapping controls are to the tool’s credit. The familiar histogram is present to the left of the image preview. Unlike the CS2 histogram which shows the luminance distribution of the HDR image, this histogram shows the distribution of the final tone mapped image. As you make changes, you can watch the histogram to determine how your settings affect the distribution.

Starting at the top right and moving counter-clockwise, there are two radio buttons that allow you to select 8- or 16-bit output. The default can be specified in an application preference; I have chosen a default for 16-bit as seen here.

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