Lens correction: Affinity Photo vs. OOC, DxO Photo Lab 2, EyeQ Perfectly Clear

[Richard Liu]

I have just noticed that the dimensions of the NEF (Nikon RAW) photos developed in Affinity Photos (both 1.6, 1.7, and 1.7.1 beta) are different from the dimensions of the same photos developed in camera (OOC), DxO Photo Lab 2 and EyeQ (formerly Athentech) Perfectly Clear.  In all cases (except OOC, of course) I am comparing the exported JPEG photos.  I would expect the OOC JPEG to be correct, since it is presumably produced with lens data available from the manufacturer, and the results from DxO to be just as good, since DxO does -- or, at least, used to do -- its own testing.  In fact, OOC, DxO Photo Lab 2 and EyeQ Perfectly Clear produced JPEGs with exactly the same dimensions (3712 x 5568 pixels), whereas Affinity Photo's are 3728 x 5600 pixels.  The camera used is a Nikon D7500 with a Nikon AF-S DX Nikor 16-80mm f/2.8-4E ED VR.  The D7500 is configured to produce RAW + NEF.  I am using the Mac versions of the mentioned application.

What is the explanation for the discrepancy?

[R C-R]

1 hour ago, Richard Liu said:

What is the explanation for the discrepancy?

It is that unlike the others, Affinity Photo does not discard any of the data from the camera sensor.

[Richard Liu]

Not sure I follow.  I am assuming that lens correction refers to barrel and pin cushion distortion.  Correcting barrel distortion involves "pinching" the sides and the top and bottom inward towards the center of the picture while keeping the corners where they are.  In order to maintain straight edges, the resulting "pointy corners" must be cropped off or empty space inserted between them.  Similarly, correcting pin cushion distortion requires "spreading" the sides and the top and bottom outward from the center of the picture while keeping the corners where they are.  In order to maintain straight edges, the "bulges" must be cropped off or new corners built up by inserting empty space.  The edges of the Affinity Photo JPEG are as straight as those produced by the other applications, and I see no empty space.

[R C-R]

It doesn't have anything directly to do with lens correction. Camera sensors collect data over their entire surface, but some of the edge data is considered unusable so it is never included in the camera's jpeg output, & most RAW developers also discard it. Affinity Photo doesn't.

[Richard Liu]

So you're telling me, Affinity Photo starts with a larger "photo" before applying the same lens correction as the other applications, so, even after correction as I described, it ends up with more pixels?  Okaaay.  I guess one can only hope that whatever is cropped off after correcting lens distortion consists mostly of edge pixels.

Do you happen to know in what sense the edge data "is considered" unusable?

[R C-R]

31 minutes ago, Richard Liu said:

Do you happen to know in what sense the edge data "is considered" unusable?

Not really, other than that it has something to do with the 'effective pixels' spec for the camera, which I think may be different for different shooting modes and/or lens combinations, but I am not sure about that.