Digital Zone System ~ 0EV as Zone 5 RawTherapee processing example

The prior Digital Zone System posts laid the foundation for actual image processing.  I now share an example of processing a 0EV as Zone 5.

Simplifications ~

I don't want to spend my time metering using a spot meter.  Instead, I let the in-camera matrix metering system do its "thang" as I feel its more than "good enough" for the kinds of scenarios I find myself in.  Using the in-camera spot-meter is always an option in those cases where I feel it would be of benefit to meter more carefully.

0EV as Zone 5 input correction curves work well for 95% of my work.  Scenes tend to be flatly lit.  Often whites slide down the tonal scale and blacks crawl up, which means the tones I want to manage are all on the linear portion of the curve.

-1EV as Zone 5 input correction curves work well for me in high contrast situations, such as brightly lit, strong contrast situations.  In those cases (around 5% of my personal work) I see a benefit for expanding tonal separation in the light areas.  Certainly I can shoot everything at -1EV and process accordingly, but this really isn't necessary (see prior paragraph).  Besides, as ISO rises, so can noise in the shadow areas. 

I put as many settings tuned the way I want into the input correction curve recipe that I've saved from my calculations as possible.  These include Capture Sharpen, vignetting the edges, auto-lens correction, luminance exposure curves, luminosity black and white conversion, and a Camera Profile that interacts well with the luminosity conversion for maximum tonal separation in a single action.

RawTherapee 0EV as Zone 5 Image Processing ~

Opening an Image

 

Essential Elements -

• AMaZE de-mosaic used for low ISO images
• LMMSE de-mosaic is selected for ISO > +/- 1000 (depending on the sensor)
   

Applying Input Correction Tone Curve

Essential Elements -

• Luminosity Black and White conversion
• Luminance exposure curves 1 and 2
• Auto-lens Correction
• Capture Sharpen
• Vignetting the edges to taste
• Camera Profile with "Tone Curve" disabled 

Note: For my work I like Sony Standard and Vivid Camera Profiles.  In concert with Luminosity Black and White conversion they give additional tonal separation, this time in the color dimension (where the Digital Zone System is applying tonal separation in the exposure dimension).

Setting Black and White Curve Points

Essential Elements -

• Watching the histogram to verify where pure white and black is in the image, move Tone Curve 2's end points
• Upper right edge of the curve is white
• Lower left edge of the curve is black

In this example I see by examining the histogram in the upper left corner of the display that the highlights are correctly expressed. So all I needed to do was move the bottom left corner of Tone Curve 2 slightly to the right to get the blacks to turn pure black (again, see the histogram in the above image).

Note:  I realize many software do not offer a second Tone Curve.  In those cases it might be worth exploring other tone tools.  There should be tools with sliders for setting the black and white points.  I don't want to disturb the carefully constructed input correction curve.

Rotation, Cropping and Vignetting

Essential Elements -

• Align the verticals/horizontals to taste by rotating the image (where necessary)
• Crop the image to taste (since I tend to crop in-camera I often just shoot at 4:3 and call it good)
• An overall Vignette is already set in my input correction curve recipe, but...
• Now is a good time for me to dodge/burn or add vignette (as I've done to the bottom of the image in this example)

Adding a Pt/Pd Tone

Essential Elements -

•  I've found I enjoy the tints and tones of Pt/Pd images and have created and stored as recipes a number of tints that I can select from
  

Output Image

Essential Elements -

• For the "internets" is downsize the original image, and...
• I often ask the software sharpen the output once more
  

With relatively few inputs I'm able to generate a rather pleasing image (to me, at least).  Every tone is properly expressed.  Nothing is "blocked up."  The light areas positively "glow." 

Digital Zone System (Part Six) ~ Resources and Inspiration

I'm concerned that I've missed something or that I've misunderstood things.  Are there errors in my own thinking and methods?  No doubt.  If readers would like to help me better understand, I'm all ears.

Resources ~

Other than a ton of YouTube videos that erroneously describe how to meter for the Zone System in digital, there are few resources on the internets (again, thank ewe George Bush the Younger). 

Alan Ross Photography:  Can the Zone System Go Digital?

Photography Cheat Sheet: Using the Zone System for Ideal Exposures

Zone VI workshop - the fine print by Fred Picker - One of the most important Zone System references from the film era 

Zone System Manual by Minor White - This is the reference I used.  There's an "eye match" method for setting up the Zone System with film that I found to be very useful. Unfortunately the link to this is just a sample, so if you're interested you'll have to find a used book somewhere.

Another look at the Zone System (film and early digital)

I started a conversation on Pixls.us on the topic.

On Zone System evolution - Zone 9 was pure white early on, and later was changed to Zone 10?  I never knew this and am left wondering why the change?

What I've decribed as a Digital Zone System is not without its dissenters. There is a well-known commenter on camera gear who said -

"For me, it means forget the Zone System when you’re using digital cameras, except as a way to describe tones. Compared to the tools available on modern cameras, it’s crude and in accurate..."

Take from it what you will.

Inspiration ~

When I recently restarted work on a Digital Zone System my earlier life came flooding back.  

I was heavily influenced by Ansel Adams and Minor White for what they had to say about the technical aspects of the film-based Zone System.  I used a Pentax 1degree Spotmeter and calibrated my films and processing to the best of my abilities.  I read through Fred Pickers book on the Zone System, too.  Every photography exhibition I could find in the LA Basin saw my shadow on its doorstep.  Looking at what was possible in expressing a final image impressed me greatly. 

Here are just a few photographers who's works can inspire me, even today.

• Alan Ross ~ assistant to Ansel Adams
• Bruce Barnbaum
• Carl Weese 
• Chris Rainier
• John Sexton ~ assistant to Ansel Adams
• Paul Caponigro 
• Ray McSavaney ~ I wish I'd known of him earlier
• Tillman Crane

 

Bugatti Royale
Sony A6300, Sigma 30mm f/2.8 EX DN
-1EV as Zone 5
Pt/Pd tints added in processing

Digital Zone System (Part Five) ~ Tonal Separation In Three Ways

The Digital Zone System that I've written about here on my blog is just one aspect of controlling tonal separation in black and white digital photography.  

There are two other areas of control that I will now take into consideration.  Taken in total, these controls allow for much greater flexibility and ease in monochrome image creation than us old film workers could ever have imagined.

Here are three areas of tonal separation.

• Digital Zone System ~ tonal separation by exposure value
• Luminosity Black and White Conversion ~ tonal separation by Human Perception Modeling
• Color Contrast Management ~ usually thought of as filtration for color separation (as we did when shooting with B&W film)
  

Digital Zone System ~

As I've already covered in depth methods for controlling the Digital Zone System, I'd like to stress just one thing.  Even though I've written a lot about using -1EV as Zone 5, I've found that generating an input correction curve for 0EV as Zone 5 can yield excellent results.  Not the least of which can be a measured improvement in all the work I've done over the years before coming to the realization of the benefits of shooting -1EV as Zone 5.

Luminosity Black and White Conversion ~

While I've written about the benefits of performing a RawTherapee Luminosity black and white conversion, I believe it's worth revisiting the subject in light of the Digital Zone System.

First, I never use simple desaturation.  As readers will recall, Human Perception Modeling shows how viewers of black and white images see the tones of red, green, blue differently.  Desaturation makes the tones of equal energy colors the exact same tones of gray.  I don't want that.

Luminosity conversion from digital color into monochrome takes into account how humans see red, green, and blue.  In short, Luminosity conversion when combined with the Digital Zone System gives us a further improvement in tonal separation. 

Second, there is a color management detail that applies directly to tonal separation in black and white work. In Camera Profile there are several  selections. One is "Tone Curve" and two others are "Base Table" and "Look."  "Base Table" and "Look" manage colors.

With the Digital Zone System I disable "Tone Curve" because I insert control over the exposure value tonal range by applying an input correction curve.

Enabling either a standard or vivid Camera Profile and enabling "Base Table" and "Look" corrects colors at the post-demosaic stage.  This is important.  The process now becomes:

• Apply input correction curve
• Specify a standard or vivid (for increased color contrast) Camera Profile
• Disable "Tone Curve"
• Enable "Base Table"
• Enable "Look"

• Select Luminosity black and white conversion

We now have tonal separation in two flexible, controllable, and measurable dimensions.

Color Contrast Management ~

Now that we have tonal separation manged two ways, Digital Zone System and Luminosity Human Perception Modeling, we can add a third.

Using the Channel Mixer we can approximate filters used in black and white film work.  For instance, we can use a red filter to deepen blues, yellow filters to lighten greens, and blue-green filters to approximate the color spectrum response of Orthochromatic and wet-plate collodion.  Further, there is sufficient flexibility in the Channel Mixer that we can create any filter we want.

The use of these tools is less measurable and more "intuitive."  We can change settings until we like what we see. 

Taken in total, we now have tonal separation in three flexible, and controllable dimensions.

 

Sony A6000, Sigma 19mm f/2.8 EX DN
-1EV as Zone 5 Digital Zone System
Pt/Pd tints applied in processing

Digital Zone System (Part Four) ~ Concise Guide to the Entire Imaging Pipeline

Using the Digital Zone System input correction curve generated in Part Three, Here is a high level overview of the entire imaging pipeline.  Remembering that RAW files are essential in this process for retaining tonal values:

Metering ~

Easy Peasy Approach

• Let the in-camera matrix metering system do its job

Note: I've found this is good enough for me in 99percent of the cases I encounter.  The metering system knows how to balance tonal distribution quite nicely.

Intentional Approach

• Using the in-camera "Spot" meter, place tonal values 

Note: Taking time to spot meter a scene can yield accurate exposures per a photographers intentions.  This can work well with stationary subjects, or working in an environment where the lighting is stable (unchanging). 

Exposure ~

0EV as Zone 5

• Release the shutter

-1EV as Zone 5

• Set the exposure system to -1EV
• Release the shutter 

 Note: I've found I can work quickly and efficiently when under-exposing at -1EV and combining it with the Easy-Peasy Metering Approach.

Processing ~ 

• Import RAW image into a software for processing
• Apply the Digital Zone System corrective curve (created in Part Three)
• Watching how tones are distributed in the histogram
• Move the top of the curve to just above pure white
• Move the bottom of the curve to just below pure black
  
• Using normal image processing tools, modify contrast and brightness to taste

Note: RawTherapee comes with minimally four curves.  Two are found under the Exposure tab.  Two more are found under the Black and White controls.  Working with just the Exposure tab, the input correction curve will be found as Curve 1.  Using Curve 2 (also set to Luminance), setting the pure white and pure black values is a very simple exercise of moving the Curve 2 top and bottom points.

 

Sony A6000, Sigma 19mm f/2.8 EX DN
-1EV as Zone 5
Matrix metering
RawTherapee processed per above
Pt/Pd tints

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."

Digital Zone System (Part Two) ~ Concise Guide to System Characterization

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

None of this Zone System stuff is magic.  Hopefully what I write about is easily understandable, easily duplicated and quickly adapted by interested parties. 

In this, Part Two, I will present a process for understanding camera/software interactions at the very front end of the RAW image processing pipeline.  It sets the foundation for something that leads directly to Part Three. There, I will present a simple process for generating an accurate Digital Zone System tone curve tailored to systems interactions between camera sensors and software.

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 Zones 0 through 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 highlight compression
• "Camera Profile" normally tries to adjust 0EV to 76(hexidecimal)/118(decimal) on all three channels (RGB) or something thereabouts, depending on the "look."

Building a Sensor/Software Step-Wedge ~

To understand how B&W tones are distributed at the start point for image processing, here is a method that I've found instructive.

Image creation ~

• Photographing a continuous tone scene (ie: blank wall, or blank sheet of paper)
• Setting the focal point well before or well behind the subject (to even out any textural/tonal variations of the blank subject)
  
• Shooting RAW
• Set ISO to lowest non-synthetic value (some camera systems allow for low and/or high ISO settings that "massage" RAW information, which we want to avoid for this procedure)
  
• Set the meter to "Spot" (to avoid problems of uneven field illumination, ie: lens vignetting)
  
  NOTE: I've found it easiest to set a camera on a tripod for this work to introduce as few lighting variables as possible
  
  
• Make an exposure at 0EV
• Increase exposure 1EV
• Make an exposure
  
• repeat this step to +4EV
  
• Make an exposure at -1EV
• Decrease Exposure by -1EV
• Make an exposure
  
• repeat this step down to -7EV or -8EV
  

Image processing ~

• Load RAW files into image processing software
• Convert to B&W (I use Luminance B&W conversion for its human perception properties)
  
• For each image...
  
• Mouse over the center of the image (where the Spot meter read the scene) 
• Note the Luminance value
  

After carefully noting the values from -7EV/-8EV through +4EV, you should have something that looks like the following.

In the example above I used a Sony A6300, Sigma 24mm f/3.5 DG DN focused to infinity, and photographed a blank white board.  It's easy to see that 0EV is _not_ 76(hexidecimal)/118(decimal).  That, in fact, is one of the roles of "Camera Profiles" when it applies a Tone Curve.

I'm exerting control over tonal values as early as possible in the process.  RawTherapee allows users to re-define the "Camera Profile" step.  In Part Three I will share how I define a new "Camera Profile" tailored to Digital Zone System work. I'm not aware of any other image processing software that allows for this kind of early intervention and I'll try to remember to describe the advantages of this in a future post.

As far as I understand the current State of Things, all other software use pre-defined "Camera Profiles" to get a RAW file to the point of image processing as quickly as possible.  What I present here in Part Two should be usable in all cases.  If what you see more closely matches the Digital Zone System synthetic step-wedge "out of the box", you're likely "good to go", within certain limits, such as accepting Zone 9 as pure white and associated highlight attenuation.

An interesting aside: The old Film Zone System described an 11EV or 11 f-stops of dynamic range.  From the above we can see that in Sony APS-C and before any further intervention that I have 12EV or 12 f-stops of dynamic range.

All this aside, the important point of this Part Two exercise is to understand how close we are to the old Film Zone System 1EV per Zone step ideal.

Digital Zone System (Part One) ~ Concise Guide to Step Wedge simulation

[Updated 7 October, 2024 ~ Important correction: Zone 5 at 0EV is 76hex/118decimal, not 7F/127 as I previously wrote.  The step wedge illustration has been updated as well]

There are no secrets to any of this, but I realize I moved rather quickly through a lot of material in my rush to understanding digital sensitometery and developing a decent black and white Digital Zone System solution.  Working in three parts, I will now try to show how anyone can do what I've done and make sure they, too, can achieve accurate results.  

This, part one, presents a recipe for generating a synthesized step-wedge.  Part two will present a process for understanding camera/software interactions which will lead directly to part three where I present a simple process for generating an accurate Digital Zone System tone curve tailored to cameras and image processing software.

Definitions ~

• Working toward a solution for black and white imaging (I may deal with color in the future)
  
• Using Luminance curves only (other curves will distort the color space which can impact the final result)
• Zone 5 shall be 76(hexidecimal)/118(decimal) or "middle gray"
  

Assumptions ~

• Digital Zone System Zones 0 through 8 are separated by 1EV per Zone
  
• "Camera Profile" normally tries to adjust 0EV to 76(hexidecimal)/118(decimal) on all three channels (RGB) or something thereabouts, depending on the "look."
  

Building a Synthetic Step-Wedge ~

Using an image processing software ->

• Create an image filled with 76(hexidecimal)/118(decimal) tone value
• Increase Exposure 1EV
• Note the new tone value
• repeat this step until you've found pure white - FF(hexidecimal)/256(decimal)
• Restart this process using the image filled with 76(hexidecimal)/118(decimal) tone value
• Decrease Exposure 1EV
• Note the new tone value
• repeat this step until you've found pure black - 00(hexidecimal)/0(decimal)

Carefully noting the values from -7EV through +4EV, as in the following.

 

Zone 5 as 0EV and -1EV
set to
#76/118decimal luminance value

Noting the decimal equivalent value in the event the image processing software uses that system (such as in RawTherapee), where the Gimp reports values in hexadecimal.

• 02(hexadecimal)/02(decimal) -7EV
• 04(hexadecimal)/04(decimal) -6EV 
• 08(hexadecimal)/08(decimal) -5EV 
• 11(hexadecimal)/17(decimal) -4EV 
• 1B(hexadecimal)/27(decimal) -3EV 
• 28(hexadecimal)/40(decimal) -2EV 
• 3A(hexadecimal)/58(decimal) -1EV 
• 76(hexadecimal)/118(decimal) -0EV 
• AD(hexadecimal)/173(decimal) +1EV 
• CB(hexadecimal)/203(decimal) +2EV 
• F5(hexadecimal)/245(decimal) +3EV 
• FF(hexadecimal)/256(decimal) +4EV

 

Zone 5 as 0EV and -1EV
set to
#76/118decimal luminance value

We will work with these values in part three.  

For the moment, note the difference where +4EV is pure white in digital work, and remembering +5EV is pure white in film work.  We will also use this knowledge in part three.  

Also note that exact 1EV tonal separation exceeds the original film Zone System definition by providing potentially usable information down through -7EV, or Zone -2.  This will "work" if the camera/sensor/software systems allow.