Thursday, 3 March 2016

Looking into Lens Corrections

From time to time, people ask why Olympus or Panasonic lenses are not listed in the Lens Profiles of Lightroom. The confusion is both from us for not seeing the clues and from Adobe for poor user interface / communication of the message to the end user.

What do people mean by Lens Corrections?

Lenses are physical designs and have optical imperfections in creating the image. Designers choose to reduce these imperfections to the minimum but that impacts lens bulk, size, number of elements and cost. Or thinking the other way, lens designers in the digital world, can purposely design imperfect lenses and rely on the camera firmware or computer software to correct them.

The imperfections cover:
  • colour fringing (sometimes called Chromatic Aberration)
  • optical vignetting falloff (darkening of the image corners)
  • curvilinear distortion (straight lines becoming bowed inwards (pincushion) or outwards (barrelling)

Where are the correction parameters stored?

Correction metadata can be stored
  • single Lens Correction Profile in separate files one file per lens. Separate files are useful when a user voluntarily carries out the measurements and submits them to the software vendor (e.g. Adobe).
  • stored as an "internal" integrated database supplied with the software program
  • stored in lens firmware which is then copied by camera body and saved as metadata in the raw file
  • stored in lens firmware which is then applied by camera body to the camera JPEG. In which case the SOOC (Straight Out Of The Camera) JPEG does not separately store the parameters, the JPEG is considered the corrected and finished image.

What do software user interfaces look like when they acknowledge the lens identity?

Adobe Lightroom Lens Correction panel in the Develop Module

 Above, you see the Adobe Lightroom Lens Correction panel in the Develop Module. This is what the panel looks like when the lens is recognised by Lightroom. You don't have to take any action. If you click on the Information (i) icon, you will see a dialog stating what the lens model is.

Adobe Lightroom Lens Correction panel in the Develop Module

Above is the Lightroom Lens Correction panel if you explicitly click on the checkbox "Enable Profile Corrections" - presumably, if the lens is already in the internal database, the information it already knows is ignored and you can nominate the individual Lens Profile files that Adobe has supplied or you have created yourself or that you have downloaded using the Adobe Lens Profile Downloader.

Adobe Camera Raw Lens Correction Panel
Similar to Adobe Lightroom's panel design, this is the Adobe Camera Raw Lens Correction panel. Note that this panel is more informative - you do not have to click one more time to display the identification / name of the lens

If you get an .lcp file from a third party, to allow Lightroom and Adobe Camera Raw access to it, put the .lcp file in
C:\Users\yourusername\AppData\Roaming\Adobe\CameraRaw\LensProfiles\1.0\Downloaded

DxO ViewPoint 2 Distortion Correction Panel
Above is the DxO ViewPoint 2 Distortion Correction Panel. Presumably the DxO Optics user interface will be similar. Note that DxO not only identifies the lens, it also identifies which body it is fitted on. This extra information might be used in their corrections.

Corel Aftershot Pro 2 Lens Correction Panel

Above is the Corel Aftershot Pro 2 Lens Correction Panel. It too identifies the camera body and the lens. Clicking "Enable Correction" does not appear to disable Correction, does it enable Correction and not ticking it ignore Correction? Chromatic Aberration and Vignette Correction are not automatically ticked when you tick Enable Correction. 

Raw Therapee Lens Correction Panel
Raw Therapee is a free raw editor. I don't see information about whether it has or knows how to use an internal database. But if you choose to use a Lens Correction Profile, the resulting file selection dialog will refer to Adobe's nest of folders on your computer.

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