a7x, a9 PDAF stripe noise technical analysis, part deux

Started 7 months ago | Discussions thread
JimKasson
OP JimKasson Forum Pro • Posts: 20,201
Stacked dark frames with a9
4

I took 768 ISO 100, 1/1000th second, uncompressed a9 dark frames captured 5 seconds apart, and computed the standard deviation of each pixel in the undemosaiced raw in a 1024x1024 area in the upper left corner.

Note that the word stacking is in the Photoshop sense, not the astronomical one: I used a set of images 1024x1024x768 to compute the standard deviations, which form an image of 1024x1024.

I multiplied the double precision standard deviation image by 100, converted it to uint16, and saved it as a 16-bit TIFF. Note: it has no gamma curve applied. PM me if you want a copy of that image.

Here's the histogram of the means of the rows before it's multiplied by 100:

And of the columns:

If you bring the (standard deviation * 100) image into Ps, boost the heck out of it and crop, here's what you see:

Notice that many pixels have the same standard deviation as their vertical neighbors.

Note also the rows with alternating pixels with standard deviation (lower is darker, higher is lighter). Those are with ones with sigmas around 3.2, I'm pretty sure.

Adam, Hank, Ilias, have at it!

Jim

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Nikon D5 Fujifilm GFX 50S Sony a9 Nikon D850 Sony Alpha a7R III +4 more
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