the last word

Photography meets digital computer technology. Photography wins -- most of the time.

  • site home
  • blog home
  • galleries
  • contact
  • underwater
  • the bleeding edge
You are here: Home / The Last Word / Pattern error in D810 dark-field images

Pattern error in D810 dark-field images

November 9, 2014 JimK Leave a Comment

I’ve been analyzing the low-frequency behavior of read noise in several cameras for the last two weeks. Now I turn my attention to how much of the dark-field images vary from exposure to exposure, and how much form a fixed pattern. In addition, I will explore the differences in the spatial spectra of the fixed and variable parts of the dark-field image.

The camera I’ve chosen for my first set of experiments is the Nikon D810, I started by making a series of dark-field exposures at ISO 1000 and 1/8000 second. I chose ISO 1000 because that is the ISO where the D810 just starts to clip the left side of the dark-field histogram. It is also the highest ISO on the camera that has no digital gain applied.

I made 256 exposures, and averaged the raw images (all four channels), recording the standard deviation of the averaged image after each exposure was averaged in:

D810averaging

You can see that the curve flattens out after about 128 images in the average, which means that there’s a portion of the dark-field image that doesn’t vary from frame to frame.

Want to see it in electrons? Sure thing:

 

D810averagingE

The electron count of the curve’s intercept with the left axis may be bigger than you’re used to seeing. That’s because I took the standard deviation of the entire frame, not of a small crop.

Then I took one of the dark-field images and measured the way that the standard deviation varied with averaging kernels of three shapes (one dimensional horizontal, one dimensional vertical, and square) and many sizes:

d810rnlpnosub

You can see that the curves flatten out, indicating that there the spatial frequency content of the dark-field image is not flat, or white, but that there is more low frequency content than would be in an image with a flat frequency spectrum.

I performed the same set of calculations after subtracting the average of 256 frames from the dark-field image:

d810rnlpsub

Now there is very little flattening of the curves — although there is some with the largest vertical kernels — indicating that the corrected image has very little additional low-frequency content over that of an image whose noise is white.

We can get another angle on it by processing the averaged image:

d810rnlp256avg

Yes, indeed. That’s where the low frequency content is. Middle frequency, too, look how the curves start to flatten for even very small kernels.

It looks like almost all the low-frequency “read noise” of the D810 can be eliminated with the subtraction of a reference image.  You deep-sky photographers might want to take note of that.

 

The Last Word

← D810 read noise characteristics vs shutter speed D810 dark-field pattern error images →

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

February 2023
S M T W T F S
 1234
567891011
12131415161718
19202122232425
262728  
« Jan    

Articles

  • About
    • Patents and papers about color
    • Who am I?
  • Good 35-70 MF lens
  • How to…
    • Backing up photographic images
    • How to change email providers
  • Lens screening testing
    • Equipment and Software
    • Examples
      • Bad and OK 200-600 at 600
      • Excellent 180-400 zoom
      • Fair 14-30mm zoom
      • Good 100-200 mm MF zoom
      • Good 100-400 zoom
      • Good 100mm lens on P1 P45+
      • Good 120mm MF lens
      • Good 18mm FF lens
      • Good 24-105 mm FF lens
      • Good 24-70 FF zoom
      • Good 35 mm FF lens
      • Good 60 mm lens on IQ3-100
      • Good 63 mm MF lens
      • Good 65 mm FF lens
      • Good 85 mm FF lens
      • Good and bad 25mm FF lenses
      • Good zoom at 24 mm
      • Marginal 18mm lens
      • Marginal 35mm FF lens
      • Mildly problematic 55 mm FF lens
      • OK 16-35mm zoom
      • OK 60mm lens on P1 P45+
      • OK Sony 600mm f/4
      • Pretty good 16-35 FF zoom
      • Pretty good 90mm FF lens
      • Problematic 400 mm FF lens
      • Tilted 20 mm f/1.8 FF lens
      • Tilted 30 mm MF lens
      • Tilted 50 mm FF lens
      • Two 15mm FF lenses
    • Found a problem – now what?
    • Goals for this test
    • Minimum target distances
      • MFT
      • APS-C
      • Full frame
      • Small medium format
    • Printable Siemens Star targets
    • Target size on sensor
      • MFT
      • APS-C
      • Full frame
      • Small medium format
    • Test instructions — postproduction
    • Test instructions — reading the images
    • Test instructions – capture
    • Theory of the test
    • What’s wrong with conventional lens screening?
  • Previsualization heresy
  • Privacy Policy
  • Recommended photographic web sites
  • Using in-camera histograms for ETTR
    • Acknowledgments
    • Why ETTR?
    • Normal in-camera histograms
    • Image processing for in-camera histograms
    • Making the in-camera histogram closely represent the raw histogram
    • Shortcuts to UniWB
    • Preparing for monitor-based UniWB
    • A one-step UniWB procedure
    • The math behind the one-step method
    • Iteration using Newton’s Method

Category List

Recent Comments

  • Brian Olson on Fuji GFX 100S exposure strategy, M and A modes
  • JimK on Picking a macro lens
  • JimK on Picking a macro lens
  • Glenn Whorrall on Picking a macro lens
  • JimK on What pitch do you need to scan 6×6 TMax 100?
  • Hatzipavlis Peter on What pitch do you need to scan 6×6 TMax 100?
  • JeyB on Internal focusing 100ish macro lenses
  • JimK on How focus-bracketing systems work
  • Garry George on How focus-bracketing systems work
  • Rhonald on Format size and image quality

Archives

Copyright © 2023 · Daily Dish Pro On Genesis Framework · WordPress · Log in

Unless otherwise noted, all images copyright Jim Kasson.