Feb 1, 2010

Full Range HDR – Codicil (Compute It Right)

Nature and Landscape Photography, Full Range HDR, FRHDR, HDR, Merge to HDR, CS4, ©Joe  Bridwell

Walking along the golf course, watching for whizzing golf balls, I was listening to PhotoNetCast podcast # 27 - HDR Photography.  At PhotoNetCast, an international panel of amateur and professional photographers shared divergent opinions on this HDR podcast.
With my attention split between listening, walking, and watching - I almost missed the seemingly stray comment, "Sometimes, I have to use Merge to HDR in Photoshop because Photomatix does NOT cleanly remove all chromatic aberration."  Fortunately, the Apple iPod Touch lets me hit one button and backup 30 seconds just to 'hear that again'. 

Pain in the …
I'd just spent about six hours removing noise and chromatic aberration after a quick Photomatix compilation of a full range HDR image.  Since I can only handle about two hours a pass at hi-res pen tablet work, it'd taken quite a while to mask offending edges of one HDR image.  Matter of fact, I even put off doing the second scene - this sort of mundane activity is much too mind numbing. 
In this situation, chromatic aberration is a blurring of boundaries which requires clone tool usage at 600% (OpenGL video card preferable) where you can see down to pixel level in your image.  With Photoshop tools, one spends the time doing computations rather than diligently hand correcting with a ‘slow’ pen and Wacom tablet.

Software and Computation Considerations
Photomatix can process 10 Full Range HDR images in a short period of time (minutes).  Unfortunately, when you blow those images up to 600%, both noise and chromatic aberration is quite prominent.  Photoshop takes several hours to process the same 10 images; but that's computer time not eye-and-back-strain time.  So, you go take care of something else...
Don't let the several hours give you any pain.  I use a dual 1.86 GHz CPU system with CPU sharing enabled.  I notice Photoshop really only uses one CPU effectively during this merge.  More recent 64 bit systems, faster CPU’s, and real dual CPU usage would significantly cut that computation time.

When done, the Full Range HDR image can then be color-balanced with global tone mapping in Lightroom before finishing up with sharpening in Pixel Genius Photokit Sharpener, a Photoshop plug-in.

All considered, once again Photoshop’s superior performance provide the subtle image control which fine art deserves.

Damn; that whizzing golf ball went on by this time...!