The whole question of lens sharpness...

Started Jun 12, 2013 | Discussions thread
Detail Man
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Re: DxO Labs' "Lens Softness" Corrections
In reply to GaryW, Jun 22, 2013

GaryW wrote:

Alphoid wrote:

olliess wrote:

Alphoid wrote:

In theory, given a perfect model of the lens, I can completely undo any blur caused by the lens.

I took this statement to mean just what it said, namely that you could undo any blur given a perfect knowledge about the blur function of the lens. To me, that means lens defects, diffraction, defocus, and anything else that modifies a point in the image.

My comment was, specifically, any blur caused by the lens. Diffraction, limited depth-of-field, antialiasing filter, resolution limits of the sensor, etc. are not caused by the lens. You would have those even with an ideal lens.

Diffraction is cause by the aperture within the lens-system - and diffraction, antialiasing filter, and resolution limits of the sensor all result in effects influencing the shape of the system PSF.

Some of these are removable, and some are not. Chromatic aberration, spherical aberations, etc. are caused by the lens.

I had one photo in particular that was a bit unsharp due to diffraction -- not exactly blurry, but you could tell it wasn't sharp if you zoomed in -- and deconvolution completely rescued it. It was like the blurriness was not even there.

I have less luck with countering poor focus, but for slight diffraction, it seems to work fine.

In addition, it's what DxO uses (I think) for their "lens sharpness", to counteract the effects of unsharp lenses, particularly in the corners where they use more intensity to counter the greater softness. This seems to work to a large extent.

The only published mention of deconvolution-deblurring being used in DxO Labs' "Lens Softness" corrections that I know of is here (see the portion of the quoted text I have underlined below):

Lens Softness correction

Lens softness’ is the intrinsic degradation of sharpness introduced by an imaging device (camera body plus lens). In image processing terms, this is a local, color-channel dependent, anisotropic convolution of the original image, which results in a 'blurry' image. In terms of image spatial frequencies, ‘blurriness' refers to how well low spatial frequencies are reproduced in the image.

You may be familiar with these concepts if you are familiar with MTF (Modulation Transfer Function) curves. DxO Labs has developed a unique unit called the BxU (Blur eXperience Unit) which is a mathematical way of describing this 'blur'. Reducing the ‘lens softness’ or 'blur' or 'lack of sharpness' means performing local, color-channel dependent and anisotropic deconvolution of the image produced by the camera.

Furthermore, DxO deblurring uses a complex contextual approach taking into account both local noise and local detail level in the image. As a result, deblurring will be automatically reduced in uniform areas (like a pure blue sky.), but increased in a detailed zone.

http://www.beautiful-landscape.com/Thoughts35.html

In a private written communication in 2010, a DxO Labs employee stated to me a confirmation that DxO Optics Pro "Lens Softness" does (in-part) utilize "deconvolution deblurring". Here is their present information describing it in general terms:

http://www.dxo.com/intl/photography/tutorials/enhance-sharpness-your-camera-dxo-optics-pro

As the DxO RAW Optics Correction Modules for a given camera-lens combination appear (to me) to in general to be significantly more effective than the DxO JPG Optics Correction Modules (for the same camera-lens combination), I think that it (may) be the case that some of the related processes may proceed on a RAW-level prior to de-mosaicing of the RAW image-data.

This approach is distinct from the deconvolution-deblurring that occurs in the sharpening tools of Adobe Lightroom, Camera RAW, Photoshop, the PS/LR plugin Topaz Infocus, as well as RAW Therapee's R-L DD - all of which appear operate on what is already de-mosaiced image-data.

DM ...

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