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D810 dark-field pattern error images

November 9, 2014 JimK Leave a Comment

In the preceding post, I presented data about the D810 fixed pattern read errors and the results of using averaged dark-field images to correct the fixed part of the read errors. We found that almost all of the low-frequency componts of the read errors were fixed — they didn’t change from exposure to exposure.

Now I’lll show you some sample images. As usual in this read noise analysis series, they have been scaled into the range [0,1],  have had a gamma curve of 2.2 applied , been res’d down to 640×480, and JPEG’d.

A sample dark-field image:

Uncorrected Image
Uncorrected Image

The reason it’s so dark is that hot pixels control the scaling.

The 256-exposure averaged image:

Averaged Image
Averaged Image

It’s at least as dark, because the hot pixels are part of the fixed pattern.

The result of subtracting the averaged image from the uncorrected image:

Corrected Image
Corrected Image

Can’t see much, can you? Lets do some low pass filtering, first with a 36-pixel square kernel.

The dark-field image:

Uncorrected Image, square kernel, 36 pixels
Uncorrected Image, square kernel, 36 pixels

The averaged image:

Averaged Image, square kernel, 36 pixels
Averaged Image, square kernel, 36 pixels

The corrected image:

Corrected Image, square kernel, 36 pixels
Corrected Image, square kernel, 36 pixels

Now with a 216-pixel square kernel.

The dark-field image:

Uncorrected Image, square kernel, 216 pixels
Uncorrected Image, square kernel, 216 pixels

The averaged image:

Averaged Image, square kernel, 216 pixels
Averaged Image, square kernel, 216 pixels

The corrected image

Corrected Image, square kernel, 216 pixels
Corrected Image, square kernel, 216 pixels

:When you look at these images, don’t judge the overall noise level; it’s all been normalized so that the range on all the images is the range of the error. Look at how pleasing or ugly the patterns are.

 

 

 

 

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