Digital Zone System (Part Three) ~ Concise Guide to 1EV per Zone Curve Generation

[Updated 7 October, 2024 ~ Important correction: Zone 5 at 0EV is 76hex/118decimal, not 7F/127 as I previously wrote.]

Finally, coming to the meat of the matter, for this, Part Three, of my Concise Guide to the Digital Zone System, I present a method for taking a newly opened RAW file and generating a correction curve that gives exactly 1EV per Zone steps from +3EV (pure white in digital work) down as far as the sensor can differentiate (-7EV or -8EV in the case of my Sony APS-C and Full Frame cameras).

Definitions ~

• Using Luminance curves only (other curves will distort the color space which can impact the final result)
• Zone 5 remains 76(hexidecimal)/118(decimal) or "18% middle gray"
• Digital Zone System Zone -2 (which doesn't exist in the film Zone System) through Zone 8 are separated by 1EV (1 f-stop for us Old Farts) per Zone

Assumptions ~

• The old film-based Zone System is adaptable to digital B&W imaging
  
• The vast majority of digital B&W output looks different from film because of digital highlight attenuation
• "Camera Profile" normally tries to adjust 0EV to 76(hexidecimal)/118(decimal) on all three channels (RGB) or something thereabouts, depending on the "look."

 

Zone 5 as 0EV ~ attenuated highlights/unbalanced "digital" Zone System  ~

Taking the EV step RAW files from Part Two...

• Use "Curves" to raise/lower each individual EV image to match the hexadecimal/decimal values indicated below
• Raise/Lower the point where the curve overlaps the narrow tone spike seen in the histogram
• Build up an overall correction curve by adding points at each EV
• Saving curve corrections as you proceed through the list (see the example below) 
  
• Once you've corrected each EV to it's respective Zone tonality value, look at the overall curve and "smooth" it by gently adjusting up/down/sideways any value that is out of line 

• Zone -2 = 02(hexadecimal)/02(decimal) -7EV
• Zone -1 = 04(hexadecimal)/04(decimal) -6EV 
• Zone 0 = 08(hexadecimal)/08(decimal) -5EV 
• Zone 1 = 11(hexadecimal)/17(decimal) -4EV 
• Zone 2 = 1B(hexadecimal)/27(decimal) -3EV 
• Zone 3 = 28(hexadecimal)/40(decimal) -2EV 
• Zone 4 = 53(hexadecimal)/83(decimal) -1EV 
• Zone 5 = 76(hexadecimal)/118(decimal) -0EV 
• Zone 6 = AD(hexadecimal)/173(decimal) +1EV 
• Zone 7 = CB(hexadecimal)/203(decimal) +2EV 
• Zone 8 = F5(hexadecimal)/245(decimal) +3EV 
• Zone 9 = FF(hexadecimal)/256(decimal) +4EV

The correction curve could look like the following, depending on where you apply the correction curve (ie: before or after applying a "Camera Profile") 

Curve that defines
Zone 9 as pure white

Zone 5 as -1EV ~ balanced "film-like for digital" Zone System ~

Again, taking the EV step RAW files from the Part Two...

• Use "Curves" to raise/lower each individual EV image to match the hexadecimal/decimal values indicated below
• Raise/Lower the point where the curve overlaps the narrow tone spike seen in the histogram
• Build up the overall curve by adding points at each EV
• Saving curve corrections as you proceed through the list (see the example below)  
  
• Once you've corrected each EV to it's respective Zone tonality value, look at the overall curve and "smooth" it by gently adjusting up/down/sideways any value that is out of line

• Zone -2 = 02(hexadecimal)/02(decimal) -7EV
  
• Zone -1 = 04(hexadecimal)/04(decimal) -7EV
• Zone 0 = 08(hexadecimal)/08(decimal) -6EV 
• Zone 1 = 11(hexadecimal)/17(decimal) -5EV 
• Zone 2 = 1B(hexadecimal)/27(decimal) -4EV 
• Zone 3 = 28(hexadecimal)/40(decimal) -3EV 
• Zone 4 = 53(hexadecimal)/83(decimal) -2EV 
• Zone 5 = 76(hexadecimal)/118(decimal) -1EV 
• Zone 6 = A0(hexadecimal)/160(decimal) -0EV 
• Zone 7 = D9(hexadecimal)/217(decimal) +1EV 
• Zone 8 = E6(hexadecimal)/230(decimal) +2EV 
• Zone 9 = F5(hexadecimal)/245(decimal) +3EV 
• Zone 10 = FF(hexadecimal)/256(decimal) +4EV

The correction curve could look like the following, depending on where you apply the correction curve (ie: before or after applying a "Camera Profile") 

Curve that defines
Zone 10 as pure white

Original Assumptions ~

• Successfully demonstrated (I hope) - The old film-based Zone System is adaptable to digital B&W imaging
  
• A corrective solution is found - metering accordingly, set -1EV tones to Zone 5 value - The vast majority of digital B&W output looks different from film because of highlight compression
• Again, a corrective solution is found - metering accordingly, set -1EV tones to Zone 5 value - "Camera Profile" normally tries to adjust 0EV to 7F(hexidecimal)/127(decimal) on all three channels (RGB) or something thereabouts, depending on the "look."