HDR Merge Master

A script that uses Blender's compositor to reliably merge exposure brackets to 32-bit EXR files in bulk.

Installation

Requires:

• Blender 4.5 LTS
• Luminance HDR v2.6.1

Optional:

• Hugin 2021 (aligning images)
• Rawtherapee (processing from raw files)

1. Install the required software above.
2. If the optional software is not installed, the relevant options will be disabled
3. Download the latest release and run hdr_merge_master.exe

Run From Source (optional)

This program is a simple python script that can be run straight from the .py script if you can't or don't want to use the pre-built executable. It has only been tested on Windows.

You will need:

• Python 3.5+

Install dependencies with:

pip install -r requirements.txt

Run the program:

python hdr_brackets.py

Usage

Running the script for the first time will prompt you to edit exe_paths.json to fill in the paths to your blender.exe, luminance-hdr-cli.exe and align_image_stack.exe executable files. It should look something like this (note the double backslashes; you can use forward slashes as well):

{
    "blender_exe": "C:\\Program Files\\Blender 2.79\\blender.exe",
    "luminance_cli_exe": "C:\\Program Files\\LuminanceHDR\\luminance-hdr-cli.exe",
    "align_image_stack_exe": "C:\\Program Files\\Hugin\\bin\\align_image_stack.exe"
    "rawtherapee_cli_exe": "C://Program Files//RawTherapee//5.12//rawtherapee-cli.exe"
}

Note: Do not use the align_image_stack.exe that comes with LuminanceHDR, as this is a different version which won't work. Only use the one that comes with Hugin itself.

Then:

1. Select a folder that contains your full set of exposure brackets (see Example Folder Structure below). You can now add multiple folders to the input folders for batch processing.
2. Choose a pattern to match the files (e.g. .tif to get all TIFF files). All formats that Blender supports should work, but if you want to use RAW files from your camera, you need to install RawTherapee and enable the RAW option in the UI. Make sure to match the pattern to your camera's output file format. I typically do some minor tweaks to the RAW files in Lightroom first (e.g. chromatic aberration correction) and then export 16-bit .tif files to merge with this script.
3. Choose the number of threads (the number of simultaneous bracketed exposures to merge). Use as many threads as you can without running out of RAM or freezing your computer. In my experience 6 threads usually works fine for 32 GB RAM.
4. Choose whether to align the images before merging.
5. Choose whether you want the scrpit to look for subfolders inside the selected folders recursivly.
6. Click Create HDRs, and monitor the console window for progress and errors.
7. The merged HDR images will be in a folder called Merged next to your original files. The exr subfolder contains the actual 32-bit HDR files, while the jpg folder contains tonemapped versions of those files.

Note: This tool does not do any ghost removal, so it's important that you use a steady tripod when shooting.

The intended use here is for creating HDRIs, allowing you to stitch with the JPG files (which load quickly and, being tonemapped, show more dynamic range), and then swap the JPGs out with the EXR files at the end before your final export. If you are using PTGui, you can do this using the included ptgui_jpg_to_hdr.py file - just drag your .pts project file onto that script and it will replace the JPG paths with EXR ones.

Example Input Folder Structure

The script will automatically read the metadata and determine which images should be grouped together and merged. The entire folder of images will be merged based on the pattern determined by the first set.

The bracket matching works by checking the exposure metadata of the first image and searching for the next image with the same exposure:

• C:/Foo/bar/
  • IMG001.tif - 1/4000 F/8 ISO100
  • IMG002.tif - 1/1000 F/8 ISO200
  • IMG003.tif - 1/250 F/8 ISO400
  • IMG004.tif - 1/4000 F/8 ISO100
  • IMG005.tif - 1/1000 F/8 ISO200
  • IMG006.tif - 1/250 F/8 ISO400

The script will discover that images IMG001.tif and IMG004.tif have the same exposure settings, and thus the images will be grouped into threes:

• Exposure set 1 (merged to merged_000.exr):
  • IMG001.tif
  • IMG002.tif
  • IMG003.tif
• Exposure set 2 (merged to merged_001.exr):
  • IMG004.tif
  • IMG005.tif
  • IMG006.tif

Exposures can be in any order (0 + ++, 0 - --, 0 + -, - 0 +, etc.).