Merging to 32-bit HDR

Multiple exposures of the same subject can be merged to produce an unbounded 32-bit document, which contains a significant amount of tonal range—more, in fact, than most displays outside of specialized equipment can reproduce. The resulting 32-bit image can then be edited with Photo's extensive set of tools, adjustments and filters, or it can be tone mapped in order to map the extensive 32-bit tonal range to a result that looks suitable for most displays.

To HDR merge several images:
  1. From the File menu, select New HDR Merge.
  2. From the dialog, click Add to locate and select your images.
  3. (Optional) Choose a Perspective or Scaling operation from the menu to allow for successful auto-alignment. The former applies a perspective adjustment to each image; the latter repositions and/or sizes the image layer.
  4. (Optional) If your image set contains moving subjects between each exposure, check Automatically Remove Ghosts.
  5. (Optional) Keep Noise reduction checked to enable colour and luminance noise reduction; Uncheck to disable noise reduction (you can address this post HDR merge using the Denoise filter).
  6. Click OK to begin merging the images.

The HDR merging is previewed in stages: first, the image alignment, then the HDR merge itself. By default, the merged result will then be taken into the Tone Mapping Persona for tone mapping. See Tone Mapping HDR images for more information.

Below you will see a 32-bit image being displayed as 8-bit with no tone mapping or further tonal adjustments applied. 32-bit simply contains too much tonal range to display, so we typically apply a procedure called Tone Mapping to map that tonal information to a range that can be displayed accurately. See the topic Tone Mapping HDR images for more information.

Full 32-bit range
Tone Mapped 32-bit
Before: A 32-bit image with no tone mapping—the range of 32-bit is too great to display. Instead we see an image with extreme contrast.
After: A 32-bit image after being tone mapped. The vast range of tonal information has been "mapped" to a range that can be reproduced by most displays.

Once work on a 32-bit image is completed, you may need to convert its colour format and, crucially, its colour profile if you intend to distribute or share it. For example, you might want to export as an 8-bit JPEG with an sRGB colour profile. Alternatively, if you are maintaining a lossless workflow, you can stay in 32-bit and export to a linear unbounded format.

To convert the colour format and profile before export:
  1. From the Document menu, select Colour Format and choose your desired format; for example, RGB 8-bit.
  2. A colour profile will be automatically assigned: for RGB 8-bit/16-bit documents, this will be sRGB IEC61966-2.1.
To maintain a 32-bit workflow for importing into other software:
  1. From the File menu, select Export.
  2. Choose the OpenEXR format and click Export, then specify where to save your document.