I realize I've written a fair bit about Digital Zone System RAW image processing, and then passed rather quickly to in-camera jpg generation without providing sufficient background to support my claims. I would like to fill in a few of those blank spaces here.
To start, I would like to show how I got from RAW Digital Zone System processing to in-camera jpg generation by looking at the definition of the old film Zone System, applying that knowledge to creating and then modifying a Digital Zone System Step Wedge.
I will share my in-camera jpg generated Step Wedge findings in future posts.
Zone System Definition ~
- Zones are separated by 1 f-stop/1 exposure value (EV)
- Zone 5 ~
- old film days == 18% gray
- digital tone value == #76(hexidecimal)/118(decimal)
- Pure Black
- old film days == Zone 0 at -5EV
- digital tone values == whatever the camera system can deliver (potentially/commonly different between RAW and the in-camera jpg generator)
- Pure White
- old film days == Zone 10 (last definition) or Zone 9 (earlier definition)
- digital tone value == +4EV as Zone 9 for the Sony cameras I own (this has been measured and is very important! to properly using the Zone System in digital)
Digital Zone System Step Wedge generation ~
To review how I generated a Digital Zone System Step Wedge -
- Create a small Zone 5 reference image of pure #76/118dec tone value
- Using an image processing software
- raise the EV of the Zone 5 reference by 1 f-stop
- measure and note the tone value as Zone 6
- raise the EV of the Zone 6 reference by 1 f-stop
- measure and note the tone value as Zone 7
- raise the EV of the Zone 7 reference by 1 f-stop
- measure and note the tone value as Zone 8
- raise the EV of the Zone 8 reference by 1 f-stop
- measure and note the tone value as Zone 9 <- pure white in the systems I use
- lower the EV of the Zone 5 reference by 1 f-stop
- measure and note the tone value as Zone 4
- lower the EV of the Zone 4 reference by 1 f-stop
- measure and note the tone value as Zone 3
- lower the EV of the Zone 3 reference by 1 f-stop
- measure and note the tone value as Zone 2...
- ... and continue this until the reference tonal patch image measures #00/00(dec)
Digital Zone System ~ idealized Step Wedge ~
Using the method described above, here is a Step Wedge where each Zone step is exactly 1EV/1 f-stop.
As can be seen, 1EV/1 f-stop tone separation continues to show measurable data below Zone 0/-5EV.
Digital Zone System ~ modified to a 10 Zone Step Wedge ~
There's something I learned about the Sony Creative Style treats the tone curve that I'll come to in the next post. To begin to account for this what I'm looking for here is a Step Wedge that retains good tonal separation from Zone 5/0EV down to Zone 0/-5EV, even if, in the end, Zones 0 through 4 do not exactly match the 1EV Zone System definition.
I suppose I should stop here a moment and talk a little about how old silver-halide film responded to the Zone System in the shadow areas. The world was somewhat complex back in the day, and Zones 0 through 4 were _not_ exactly 1EV separated. If you read some of the history of film you may come across tone curves that show how various film-types treated highlights and shadows.
Zone 4 into Zone 3 was particularly interesting as film was not very sensitive to dark areas. In fact, we used to say "expose for the shadows and develop for the highlights." Bruce Barnham went so far as to redefine the Zone System for his purposes to say that Zone 4 was where shadow details should be put, not in Zone 3 like the System defines.
So hold these thoughts and I'll come back to this in the next post.
Using the Step Wedge from the prior step I anchored Zones 5 through 9, then using the "Curves" function, brought the pure black point to Zone 0/-5EV, re-measured the modified Step Wedge at each Zone. Here's what that looks like.
I will use this 10EV Digital Zone System Step Wedge as my reference in trying to sort out an in-camera jpg image processing solution for Sony's Creative Style Black and White nastiness.
Stay tuned. Don't touch that dial. We will be right back. Or something like that.
