Recently, I’ve begun doing more HDR post-processing of single-shot RAW images I’ve shot using my always handy Canon PowerShot S95. This is the camera that goes almost everywhere I do – it’s in my backpack!
It’s capable of producing some beautiful single RAW HDR images – see this example that I shot last weekend in San Francisco.
Oh, by the way, I didn’t worry about lens barrel distortion when I post-processed that shot of a San Francisco Muni Cable Car!
One of the things to beware of when doing single RAW processing – particularly with compact cameras like the S95 – is just how much lens barrel distortion exists in the RAW file output by the camera. This distortion can be surprisingly significant – but it takes just a couple of additional steps in the post-processing workflow to deal with it – when required.
Note that some images, while having the distortion, look fine to the human eye without any of this additional post-processing. You’ll have to be the judge as to when to tweak further and when to accept the initial result instead.
As described in my recent photography workflow article, my S95 images all come first into Lightroom where they’re stored in my photo masters directory on an external hard drive. I use a Smart Collection in Lightroom to highlight all of the RAW images in my collection. When I’m interested in doing some post-processing, I’ll browse that collection of RAW images and then use the Show in Finder menu item to open a Finder window with that image selection. I’ll then drag that image onto Photomatix in my dock and begin the HDR post-processing. Once that’s complete, I’ll save the resulting JPEG and import that into Lightroom. It’s then that I apply Lightroom’s adjustments to deal with the barrel distortion problems – as well as dealing with any chromatic aberrations that might have cropped up along the way.
Below you can see two images that illustrate the problem – the first is the output from Photomatix following single image HDR processing. The second is the final result following post-processing in Lightroom to remove the distortion and chromatic aberration. In between, I used Lightroom’s Lens Correction adjustments to perfect the image.
First image – following single image HDR processing in Photomatix Pro:
Notice the geometric distortion in the rectangle around the Dairy’s logo. That’s the lens barrel distortion that hasn’t (yet) been corrected.
If you look closely at the right border of the logo, you can see some chromatic aberration – a bit of red that’s seeping in next to the tight border. We’ll fix that too in Lightroom!
Second image – following the use of Lightroom’s Lens Correction/Manual (mostly using the Distortion, Vertical and Horizontal sliders) and using the Red/Cyan slider in that same Chromatic Aberration section. It’s like magic how it moves those pixels around at your command!
These tiny compact cameras are wonderful for shooting RAW images on the go – but sometimes you’ll need to further refine the resulting images to square things up and correct the lens distortion when using their RAW images for single-image HDR. In an ideal world, Photomatix would be able to do this automatically when importing a single-image RAW – maybe that will come along sometime?
PS: Are you curious where I took this shot? Here’s the spot – the corner of Mission St. and Ocean Ave. in Carmel, CA. You can see the Carmel Dairy logo on the wall – presumably long protected from paint over by citizens of Carmel!