This page shows a comparison between two different ways of processing a photo taken by
Subhash with an Olympus E-5 and a Zuiko Digital ED 7-14mm
F4.0 ultra-wide angle lens. The purpose was to evaluate the distortion and chromatic
aberration.
The original image was taken in raw format. Subhash processed the image with Photoshop, and
I processed it with DxO Optics “Pro”. This was not as simple as it seems: DxO considers the E-5 to be so
much better than my Olympus E-30 that they want me to buy a different version of their product, costing
nearly twice as much. I downloaded a demo version of the software, but I couldn't install
it because I already had a newer version of the standard product installed. So I cheated
and modified the raw image to claim that it was taken on an E-30, which has an almost
identical sensor. The standard version of DxO does not restrict the lenses used. For this
reason, the EXIF data of the two sets of images makes different claims about the camera
body.
Subhash didn't give me details of what parameters he tweaked in Photoshop, and some of the
details, notably the colour rendition, are quite different. Possibly this is due to my
lying about the camera body, but it's not important enough to do anything about, especially
since DxO is glacially slow at this sort of thing. In particular, I don't think it has
influence on geometry or chromatic aberration.
All of the following images show the same part of the image, first processed by DxO, then by
Photoshop. The differences in the geometry is due to the distortion correction, and is most
obvious at the corners. Running the mouse cursor over either image will cause it to change
to the other, allowing better comparison.
The first two images show the complete 4032×3024 image. Click on either image to get up to
four different sizes, the last in original resolution.
The remaining images are 600×450 crops of each corner of the image and the centre, and
they're probably better to demonstrate the differences. The smallest version is reduced 75%
to 300×225. Click on the images once to get original size.
In summary, I think the DxO-processed images are an order of magnitude better than the ones
processed by Photoshop. The sharpness is much better, and chromatic aberration, while still
present, is significantly lower. I used default values in each case.
