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Merging to HDR in Photoshop |
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 Starting with SC2 Photoshop offers merging of several differently exposed photos to an HDR (High Dynamics Range) image. As there are many standalone programs capable of producing HDR images and in many cases solely devoted to this task we start the series on HDR with this Photoshop command lying so closely at hand.
Making hdr in Photoshop has same two steps as in any other program. First we merge several differently exposed photos to an hdr image. After that we have to adapt the resulted hdr image for accessible media through tone mapping procedure - the adaptation of high color range to the usual low range.
To make an hdr image you go to Edit > Automate > Merge to hdr. If the source images are already open in Photoshop, choose "open images", if not - you can browse for the source files on your computer.
A quite important thing to do before starting the merging process is to check the "Attempt to automatically align the source images". With this option checked the program will align together the shifted during "of-hands" shooting images. Mind only the increased time the program will need for alignment.
The result you get after the merging is an hdr image that needs to be adapted to the usual means like our monitors or even printed copies that are physically confined within a low range of colors. The existing already hdr monitors are yet too expensive and scarce to take them into account here.
The histogram on the right has a slider with which you can move the white point in the image. The changes would not influence the information contained in a hdr image but will be saved with 24 bit image if you choose to save it.
You can save the 24 bit hdr image for later viewing in one of the suitable formats (these monitors will become widely spread sooner of later) or editing with another program dealing with hdri.
Or you can perform tone-mapping in Photoshop. The tone mapping options dialogue appears after you choose to save (convert) the image into 16 or 8 bit format. Photoshop offers 4 tone-mapping methods.
Exposure and gamma adjusts the brightness and contrast for the hdr image.
Highlight Compression automatically compresses the highlight values, so they fall within the luminance values range of the 8 or 16 bpc image file.
Equalize Histogram is another automatic method that compresses the dynamic range of the HDR image while trying to preserve some contrast.
Local Adaptation allows adjustment of the size of the local brightness regions (Radius slider) and the Threshold (tonal difference between the regions). It's the only method letting you to change the tonal curve of the image and thus the most flexible one.
Any fine-tuning is only possible in Exposure and Gamma and Local Adaptation dialogues. Let’s see what results those corrections can produce.
The changing of exposure gives us the usual effect – a darker or a lighter image. Too strong changes in the exposure can nullify the hdr effect altogether. Gamma is a more subtle instrument, but while it lightens the too dark areas, they become a bit dim, as if covered with some patina.
Local adaptation is more flexible, as it allows the changing of the tonal curve of the image. While the first picture you usually see on the screen when choosing Local Adaptation option is rather far from being suitable, the changes in the curve can produce very acceptable results with good bright colors.
The adapted to low range image can be further edited in Photoshop or simply saved into one of the usual formats.
Merging images to an hdr file is not at all difficult affair, especially regarding easy and smooth workflow. The existing tools give you all technical means for a production of a good result the rest depends on skill and taste.
To compare Photoshop hdr functions with other hdr tools see HDR tools - Comparison and HDR tools - Rating articles.
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