Adobe Photoshop CS5 for Photographers - Martin Evening [181]
Finally, we come to the Toning Curve and Histogram. You can use this to apply a tone enhancing contrast curve as a last step in the HDR conversion. The histogram displayed here represents that for the 32-bit image, but you'll find the Histogram panel in Photoshop more useful when gauging the outcome of a conversion. When you are done you can click on the OK button for Photoshop to render a low dynamic range version from the HDR master.
Removing ghosts
It is important to minimize any movement when shooting exposures, which is why it is best to shoot using a sturdy tripod and cable release. Even then there remains the problem of objects that may move between exposures, such as tree branches blowing in the wind. To help address this the Merge to HDR Pro process in Photoshop CS5 utilizes a new ghost removal algorithm which automatically tries to pick the best base image to work with and discards the data from other images in those areas where there is movement. When the ‘Remove Ghosts’ option is checked in the Merge to HDR Pro dialog you'll see a green border around whichever thumbnail has been selected as the base image. You can override this by clicking to select an alternative thumbnail and make this the new base image. For example, if the moving objects are in a dark portion of the photograph then in these circumstances it will be best to select a lighter exposure as the base image. In practice I have found the ghost removal to be very effective on most types of subjects, although moving clouds can still present a problem. Skies are also tricky to render because the glow settings can produce a noticeable halo around the sky/horizon edge. This problem can usually be resolved by substituting the medium exposure sky image as a separate layer with a layer mask based on the outline of the sky.
Photomatix Pro
Photoshop's tone mapping methods are designed to help you create natural- looking conversions from an HDR to an LDR image. Photomatix Pro has proved extremely popular with photographers because it offers excellent photo merging (sometimes with more accurate image merging of hand-held shots), ghosting control and, above all, more extensive tone mapping options. Tone mapping with Photomatix Pro is much easier and also allows you to create those illustration-like effects that are often associated with a high dynamic range image look (which we should really call ‘HDR to LDR converted images’). One explanation for the difference between the Photoshop HDR conversion method and Photomatix Pro may be because Photoshop uses a bilateral filter for the tone mapping, while Photomatix Pro uses a Gaussian filter which produces more noticeable-looking halos. I like using Photomatix Pro and find it quick to work with, but I do also find the new Merge to HDR Pro in CS5 works extremely well and I now find myself split between working with both.
How to avoid the ‘HDR’ look
It has to be said that HDR to LDR converted images can sometimes look quite freaky because there is a temptation to squeeze everything into a low dynamic range. Just because you can preserve a complete tonal range does not mean you should. It really is OK to sometimes let the highlights burn out or let the shadows remain black. The Photomatix Pro program has proved incredibly popular with HDR enthusiasts, and in the process spawned the classic ‘HDR’ look, which I personally think has been done to death now. Besides, Photomatix Pro can actually be used to produce nice, subtle tone mapped results, but I suppose people don't notice these types of HDR photos quite so much. The Photoshop approach also lets you produce what can be regarded as natural-looking conversions and I think you'll agree that the Figure 7.6 example shows how the