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 / Sony a7RII FW 2.0 raw dark-field mean values vs ISO

Sony a7RII FW 2.0 raw dark-field mean values vs ISO

November 22, 2015 JimK 2 Comments

Jack Hogan, in a comment to an earlier post on the rms noise values of uncompressed and compressed Sony a7rII dark-field images, wondered if there was digital multiplication going on, and, if so, would the mean values be affected.

I took a look at the mean values of a 200×200 central square of the same raw dark-field images that I’d used for the earlier posts:

a7rii mean df

Ignore the vertical axis label; it’s just raw count. Can’t tell much with all three (r, b, and one g) channels, can we?

Red:

a7rii mean red df

Green:

a7rii mean green df

Blue:

a7rii mean blue df

The high-ISO values appear to be too noisy for much in the way of conclusions. However, at the low ISO values, there is a systematic bias, with the compressed (no suffix) means being higher than the uncompressed (“- uc” suffix) means. The difference is only about half a least-significant bit, with the uncompressed values closer to the nominal black point of 512.

It is possible that this is real. It is also possible that RawDigger’s compressed file rounding algorithm is slightly different from Sony’s. If various raw developers use different rounding algorithms, we could see raw developer dependent color shifts on extremely hard-pushed images. If the slight offset is real, then we could see raw developer independent color shifts on extremely hard-pushed images.

It is also possible that we are observing a self-heating effect; the compressed exposures were made immediately after the uncompressed ones. Nope; that’s not it; I just looked at the a7II results; where I made uncompressed, then compressed, then uncompressed again sets of exposures. I see the same kind of thing there.

The Last Word

← Sony a7RII FW 2.0 raw dark-field histograms, ISO 3200 and up Sony a7II FW 2.0 raw dark-field mean values vs ISO →

Comments

  1. Jack Hogan says

    November 22, 2015 at 1:25 pm

    Thank you for doing this Jim. It does look like the uncompressed mean black level starts rising at about ISO10,000 when the second digital scaling factor appears to kick in.

    Reply

Trackbacks

  1. Sony a7II FW 2.0 raw dark-field mean values vs ISO | The Last Word says:
    November 22, 2015 at 1:57 pm

    […] the previous post, I noted small (sub LSB) differences in average dark field images from compressed and uncompressed […]

    Reply

Leave a Reply Cancel reply

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

March 2023
S M T W T F S
 1234
567891011
12131415161718
19202122232425
262728293031  
« 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

  • JimK on Sony 135 STF on GFX-50R, sharpness
  • K on Sony 135 STF on GFX-50R, sharpness
  • Mal Paso on Christmas tree light bokeh with the XCD 38V on the X2D
  • Sebastian on More on tilted adapters
  • JimK on On microlens size in the GFX 100 and GFX 50R/S
  • Kyle Krug on On microlens size in the GFX 100 and GFX 50R/S
  • JimK on Hasselblad X2D electronic shutter scan time
  • Jake on Hasselblad X2D electronic shutter scan time
  • Piotr Chylarecki on Who am I?
  • JimK on Who am I?

Archives

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

Unless otherwise noted, all images copyright Jim Kasson.