M10M & M10-R dot artifacts in the DNGs

[t00l1024]

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Totally a thing.

The data point I can add is that on my trips down to White Sands, NM... there are grains of sand (actually gypsum sand) that glisten in the sun. It's VERY noticeable to the naked eye. I use orange & red filters there, but believe it's irrelevant for this discussion. The data point is a fine, bright light coming from a dark[er] background.

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[ramarren]

Ah. You've discovered a micro-black hole farm.

I haven't seen any artifacts like this in either my M10-M files or in the test files from the M10-R that I recently purchased. Doesn't say they don't exist, I just haven't seen them. 

G

Edited February 23, 2023 by ramarren

[adan]

I've been watching and considering this particular "black center spot" issue, and here are my thoughts:

1) I poked through a random set of pictures made yesterday with my M10-M - and hey-presto, there were some incipient dark (i.e. gray) centers showing. Note that I usually only use the M10-M for the high ISOs, so noise has meant I've never actually run across detectable single black pixels in the center of white things before.

And I have a simple multi-part optical theory about why these turn up. They are simply the recording of optical aberration of the LENS(ES), as we move to higher and higher image magnifications (more and more pixels).

Key point there - this is not a firmware problem, it is an optical problem.

There is no such thing as a "perfect" lens. The differences between lenses, regardless of cost, are always only relative (less or more CA, or less or more blur, but never zero). And the more detailed a picture of a lens's output we achieve (more megapixels), the more the remaining aberrations will become visible.

A. Bright-ring or "Soap-bubble" bokeh. This naturally renders anything not perfectly in focus, as a pool of light with a darker center, and brighter edges.

A fact that should be noted is that bokeh blurs are NOT symmetrical around the plane of focus - and a lens that produces smooth blurs in the background will produce ringed bokeh in something closer than the plane of focus, and vice versa. So no matter the lens, we will see some BR bokeh somewhere in the image - either foreground or background.

Multiple examples of this and other bokeh effects here: https://jtra.cz/stuff/essays/bokeh/index.html

Naturally, if something is being rendered as a bright circle with a darker center - even a tiny amount in a tiny area - it will be amplified more and more with major application of sharpening and contrast controls (and recall that digital sharpening IS a CONTRAST control, essentially -  it increases the contrast along edges, whether they be an edge, spot or line in the subject, or simply the edge of a pixel). All of the following are basically derivations of unsharp-masking algorithms - "simple" Sharpen/Sharpen more; Clarity; Dehaze, possibly.

B.  Longitudinal Chromatic Aberration - significant for either the M10-R (which will capture it in all its glory, and may carry that over to monochrome conversions) and the M10-M (if the remark above about the spectral sensitivity of the M10-M (more green-sensitive, less red sensitive) is accurate)

Note that long-CA produces a colored-target image from a white point. Sometimes cyan around red, sometimes red around cyan, sometimes magenta/green, depending on whether it is R, G, or B (or a mix) that is incorrectly focused. One (or two) of the colors is more blurred than the third (in this example, the blue and green produce a bigger blur than the red.)

Capture that with a sensor less sensitive to red, and the red will go black. Convert it to monochrome by darkening blues, and - presto, a blue or blue-green center will go black.

And if the blur overall is just a few pixels of a tiny detail (only slightly OOF), the dark center can easily end up as a single pixel (right side - upper right dot is simply the center target scaled down; lower right dot is "enhanced" with sharpening and contrast increase.

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2) I worked with one of the pictures with incipient dots by changing certain processing parameters.

Here is the original shot with zero processing - both the full frame for context, and 400% of an area showing (eventually) quite a few dark dots in highlights (or even gray areas). Note the picture is, at this point (yellow circle), a little blurry. Lens 35mm Summicron ASPH at f/4.

The dots in the ":" of the background sign are most obvious, but there are also a few in the OOF tail-light and "RX550" emblem.

 

This the same part of the image with a basic Photoshop "blur" - to absolutely minimize any sharpening introduced by the camera or default ACR processing - boom, the dots vanish.

 

Now here is the image with increasing amounts of sharpening - simple "Sharpen"; "Sharpen More" and USM - radius 0.3, amount 500.

Sharpen

 

Sharpen More

 

USM 0.3 x 500%

 

Now here a version with heavy additional enhancement - contrast and clarity adjustments on top of the USM. LOTS of stand-alone dark dots.

 

I question whether firmware as such can fix this (unless you trust firmware automation to be able to tell the difference between a "dark spot," and simply a distant moose-turd on the snow or sand.

 

[ramarren]

gads. you're really working hard to show a problem on that photo! 

I'm simply not that much of a pixel peeper.  

G

[adan]

Exactly!