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 / Dither and image detail, low contrast

Dither and image detail, low contrast

April 16, 2016 JimK Leave a Comment

Yesterday and the day before, I wrote a post aimed at discovering the relationship between dither and quantizing precision when resolving detail was the main criterion. The conclusion was that, just as for the avoidance of posterization (see here, here, and here), half a least-significant bit (LSB) was enough noise for most purposes. For critical judgements, it looked like 0,7 bits was slightly better.

Today I’ll repeat the experiment with a couple of changes. First, I reduced the target contrast so that the dynamic range is about 1 LSB with a 3 bit ADC. Here it is at 300% magnification.

quick fox lo c

Second, in response to a reader comment, in order to facilitate comparisons, I changed the camera simulator so that the read noise image is the same simulated voltage across all ADC precisions. Doing that without rendering the camera simulator less useful for other purposes turned out to be a little tricky. I ended up adding the ability for the simulator to work with stored pre-amp and post-amp read noise images. Then I set the post-amp read noise to zero, the unity-gain ISO to 100, the set ISO to 100, the pre-amp read noise to some value for 3 bit precision. For the four-bit precision, I set the ISO to 200, and for 5 bit precision the ISO was set to 400.

Other camera simulator details:

  • f/2 diffraction-limited lens
  • 450, 550, and 650 nm light
  • 4.88 um pixel pitch
  • Adobe RGB GBRG CFA
  • 100% fill factor
  • AHD demosaicing

Here’s a set with noise equal to half an LSB of the 3 bit converter, a full LSB for the 4 bit converter, and 2 LSBs for the 5 bit converter. Thus the noise voltage remains the same if the full scale voltage remains the same, regardless of the precision of the ADC.

3 bit precision, 1/2 LSB noise
3 bit precision, 1/2 LSB noise
4 bit precision, 1 LSB noise
4 bit precision, 1 LSB noise
5 bit precision, 2 LSB noise
5 bit precision, 2 LSB noise

Increasing the dither a bit, to 0.7 LSB of the 3 bit converter, 1.4 LSB for the 4 bit converter, and 2.8 LSBs for the 5 bit converter:

3 bit precision, 0.7 LSB noise
3 bit precision, 0.7 LSB noise
4 bit precision, 1.4 LSB noise
4 bit precision, 1.4 LSB noise
5 bit precision, 2.8 LSB noise
5 bit precision, 2.8 LSB noise

Increasing the dither  to 1 LSB of the 3 bit converter, 2 LSB for the 4 bit converter, and 4 LSBs for the 5 bit converter.

3 bit precision, 1 LSB noise
3 bit precision, 1 LSB noise
4 bit precision, 2 LSB noise
4 bit precision, 2 LSB noise
5 bit precision, 4 LSB noise
5 bit precision, 4 LSB noise

My conclusions are as before: half a bit rms of Gaussian noise is good enough dither  for most purposes, 0.7 bits is a little better, but going to 1 LSB noise doesn’t help. As before, it is apparent that increasing the precision makes the read noise less objectionable.

If anyone has ideas for other useful test targets, I’d be interested in hearing them. I may try a real scene next.

 

 

The Last Word

← Dither and image detail, AHD Dither and image detail, natural scene →

Leave a Reply Cancel reply

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

October 2023
S M T W T F S
1234567
891011121314
15161718192021
22232425262728
293031  
« Sep    

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

  • JimK on Fujifilm GFX 100 II ISO setting vs gain
  • NA on Fujifilm GFX 100 II ISO setting vs gain
  • JimK on Fujifilm GFX 100 II ISO setting vs gain
  • Nikojorj on Fujifilm GFX 100 II ISO setting vs gain
  • Brandon on GFX 100 II read noise in CH drive mode
  • JimK on GFX 100 II EDR summary
  • Denz on GFX 100 II EDR summary
  • Erik Kaffehr on GFX 100 II read noise in CH drive mode
  • UA on More on GFX 100 II electronic shutter speeds
  • Matthias on More on GFX 100 II electronic shutter speeds

Archives

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

Unless otherwise noted, all images copyright Jim Kasson.