Processing High Dynamic Range (HDR) Images in Photoshop CS5
In the March 2008 issue of the Newsletter my article on High Dynamic Range (HDR) Photography outlined the processing of HDR images in Photoshop CS3 – a process which was far from intuitive and which no doubt boosted the popularity of third party specialist software such as Photomatix. Photoshop CS4 brought no changes in this area, but in CS5 the HDR applet matured into HDR Pro which is a great improvement over it’s predecessors and which aroused Photomatix from it’s cosy slumbers and prompted the release of Photomatix 4!
The capture of bracketed exposures for HDR was outlined in the article above and will not be repeated here. Once the files have been downloaded to the computer it is not advisable to make any corrections to them whether they be jpeg or RAW and process them as they are. If you must make corrections be sure to apply the same correction to all the images to be processed. In Photoshop CS5 go ….
File > Automate > Merge to HDR Pro – the Merge to HDR dialogue box opens. Use the Browse button to navigate to the folder in which you saved the series of exposures and highlight them and click on OK. Ensure that the ‘Attempt to Automatically Align Source Images’ check box is checked and click on OK, Fig1.
Fig 1 Merge to HDR
Photoshop will now process the images which can be quite a lengthy process depending on the speed of the computer. Eventually a preview of the HDR image will appear on the screen with thumbnails of the component images along the bottom of the screen. By checking or unchecking the tick box by each image the effect of that image on the overall HDR image can be determined, Fig 2.
Fig 2 HDR Preview
The HDR Pro interface in CS5 is far more intuitive than that in CS4 and earlier. Sliders for the various adjustments to tonemap the image are shown to the right of the preview. By default the method of tonemapping is set to 16 bit Local Adaptation – a great improvement over previous versions where this very necessary option was buried deep in the menus!
A brief explanation of the adjustment options (Fig 3) ….
Local Adaptation adjusts the HDR tonality by adjusting the brightness of the image locally rather than globally.
Edge Glow (somewhat confusing nomenclature) – Radius controls the size of the local brightness areas and Strength specifies how far apart two pixels’ tonal values must be before they are no longer part of the same brightness region.
Tone and Detail – the default Gamma setting maximises the dynamic range; values <1 emphasize midtones and values >1 emphasize the highlights and shadows. Exposure is self explanatory and for Detail read Sharpness. The Shadow and Highlight sliders are used to brighten or darken these areas.
Colour – Vibrance adjusts the intensity of subtle colours and Saturation controls the intensity of all colours from monochrome (-100) to double saturation (+100).
Fig 3 HDR Conversion dialogue
The Curve (fig 4) can be used to further fine tune the tonemapping of the image. By checking the Corner box the equalisation of changes from point to point on the curve can be over-ridden and more extreme adjustments applied – the curve becomes angular. (This facility would be appreciated in the normal PS curves dialogue, but sadly it is not included)
When satisfied with the outcome click on OK to process the image and save the file as a PSD. Remember that the tonemapped image is only the starting point for the production of the final image and further adjustment in Photoshop is required using the normal techniques.
Fig 4 Curve Adjustment
Fig 5 Average Exposure (as metered) & HDR Image (both unmodified in PS)
The difference between the straight shot and the HDR image processed from a series of bracketed shots is clear, although further processing of the latter in Photoshop is clearly needed, but all the detail is there!
The ability to adjust individual colours is not available in HDR Pro, nor in Photomatix 3, but is included in the ‘new kid on the block’ Oloneo which is quite impressive in terms of speed and has an intuitive GUI. Presently in beta and is free with updates as long as the beta stage continues, it is worth a look at http://www.oloneo.com/
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