Workflow Overview

Here are the basic steps to create a multi-frame stitched HDR image:

• Convert the RAW files
• Stitch each exposure sequence
• Combine the stitched images into a single HDR image
• Do the finishing work

I will briefly describe each step.

Convert the RAW Files
I mostly use Rawshooter Premium (RSP) for RAW conversion work. Once the administrative work is complete (organizing and naming files, and doing other asset management tasks), I call up the selected images in RSP and start working on the RAW conversion. For these example images, it looks like this:

There is less work to do in this step than usual. This is because most image exposure work is going to be done later in the HDR processing. Therefore at this point I restrict adjustments to setting a good white balance, possibly adjusting the detail and noise parameters slightly, and optionally adjusting saturation slightly.

For these example images I chose a Color Temperature of 7300 and Tint of 3, slightly warmer in color tone than the “as shot” settings straight from the camera. I also gave Detail Extraction, Noise Suppression and Saturation a boost of 10 points each to liven up the images a little. These sorts of adjustments are discretionary and I could leave them out here, choosing instead to perform equivalent actions later in the workflow.

I make these changes while zoomed in on a representative frame out of the base exposure sequence. Once I am satisfied with how that image looks, I use the RSP Copy Corrections function to transfer the same parameters to all 24 images in the sequence. This ensures consistent exposure and color tone for the images when they are later stitched and tone mapped.

It takes only a few minutes to process the RAW files into 24 TIFF images, each saved at 16 bits to maximize DR retention. Then I am ready to start the stitching work.

Stitch Each Exposure Sequence
With 24 TIFF images representing three separate exposure sequences of eight frames apiece, I will need to perform three separate stitching operations – one per exposure sequence. For convenience, I separate each group of eight images into a different temporary folder.

Using Panorama Factory (PF), I will start by stitching the base exposure sequence. If I need to manually fine tune any of the automatic results using PF’s tiling system, it is easiest to see most of what is going on in these exposures. The others are too dark or too light in key areas. That same fact may cause trouble for the automatic stitching algorithms as well, another reason to start with the base exposure sequence. Working through the wizard interface is straight forward and brings me to this point after about three minutes of processing:

Key settings I made while working through the wizard included:

• stitch in fully automatic mode
• specified lens focal length, enabled corrections for lens barrel distortion and brightness falloff
• automatically fine tune, do not sharpen
• enable exposure matching but not exposure correction (since exposure work will be done in HDR, I do not want PF doing anything to exposure other than ensuring a smooth blend)
• process the output for maximum image size

When I examine the results of the auto-stitch, I do find a lot of alignment problems, mostly within the foreground rocks. (Using a lens with little distortion helps minimize alignment problems where the software could not fully correct for lens distortion.) I correct these using PF’s tiling system which allows selective overrides of the automatic stitching. This type of work takes a long time to do, and is a big reason why it is desirable to process all stitches with the same set of control points. (In fact, if you could see the image at full scale you would realize that I did not complete the fine tuning. I had time to fix only three out of the seven overlap regions, but it is not noticeable at small resolutions.)

Unfortunately, PF does not support reusing a set of control points on another stitch sequence; this is at the top of my personal wish list for this tool. There is a “hack” that will trick the tool into processing a different set of images using a project file set up for a previous image sequence. However this trick is unsupported and may cease to work after some future release of the application. In the meantime, I use it to process the remaining two exposure sequences using the same control points established for the first sequence.

I now have three stitched images (saved as 16-bit TIFF files) as my exposures to feed into HDR processing:

0 EV base image

-2 EV image

+2 EV image

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