Color Negative Inversion

Process based on the work by Aaron Buchler https://github.com/abpy/color-neg-resources.

The following process provides a well-informed, accurate, and flexible method for converting negative images to positive in Photoshop. Aaron Buchler's semi-automated method for converting negatives in 32-bit serves as the foundation for this approach, which simplifies and streamlines the original workflow.

Kodak Gold 200 negative shot with a Canon EOS50e and Canon EF 100 mm f/2.8. Negative illuminated with an iPad screen, photographed with a Sony A7IV, processed with the method described below.

more at www.alchemycolor.com

contact: info@alchemycolor.com

1. Prerequisites

Installing presets and profiles

Install the XMP preset. This preset reverses the effect of the default tone curve of the Adobe Standard profile. This is a fundamental part of the conversion.

Copy "🜃 Adobe Standard to Linear.xmp" to:

• Mac: Users/[username]/Library/Application Support/Adobe/CameraRaw/Settings/
• Windows: C:\Users[username]\AppData\Roaming\Adobe\CameraRaw\Settings

If by any chance you don't have the REC.2020 profile installed in your system.

Copy "Rec. 2020.icc" to:

• Mac: /Library/Application Support/Adobe/Color/Profiles
• Windows: C:\Windows\System32\spool\drivers\color

2. Preparing the negative in Adobe Camera Raw

• Load a RAW file. While experimenting with JPEG or TIFF scans is possible, the results will generally be inferior.

• For DSLR scans

  • White balance to a known dark neutral area of the photographed scene, a deep shadow for example. A dark photographed color will appear brighter in the negative, hence, look for a bright area in the negative. Don't use the burned film tip and transparent film base as these sit outside the usable dynamic range of the film.
  • Don't white balance JPEG or TIFF images.
  • Load the “🜃 Adobe Standard to Linear” preset. This preset loads the Adobe Standard DNG profile and a curve that modifies the default tone curve of Adobe Standard to linear.
  • Set color noise reduction to 0 to preserve the natural film grain.
  • Open or export as TIFF 16 bit in REC. 2020 color space.

• For DNG images originated from scanner software such as Vuescan.

  • You will probably see the DNG profile set to "Embedded".
  • Don't white balance the raw scan as the embedded DNG profile most likely is empty, thus resulting in inadequate color when setting large white balance swings such as the ones originating from the film base. Density balance will take care of this further down the line.
  • Load the “🜃 Adobe Standard to Linear” preset. This preset won't the Adobe Standard DNG profile as it most likely isn't supported for Vuescan DNGs. Experiment wether or not the custom curve that transforms Adobe Standard to linear results in better inversions.

NOTES

• A fundamental initial step in this whole process is preserving the linearity of the negative reproduction of the negative. The curve loaded by the provided preset preset draws the reverse shape of the tone curve of the Adobe Standard DNG profile.
• Adobe Standard as a base DNG profile is used in this method for the sake of compatibility as the vast majority of digital cameras are supported.

3. Reversing the negative

• Run the “🜃 1. Convert to 32-bit” action. This will convert the image to 32-bit and the color space to REC.2020 if it hasn’t already been converted.
• Use the eyedropper tool to select background and foreground colors. Whenever possible, choose neutral areas within the photographed scene. A color checker image illuminated under a known light source is highly beneficial at this step, as it ensures accurate and consistent color balance for other photos in the roll. Minor white point variations can be adjusted in another layer.
• Pick dark neutral: ALT+click on a neutral, bright part of the negative.
• Pick bright neutral: Click on a neutral, dark part of the negative.
• Run the "🜃 2. Load density balance script" action. This action prompt you to load the density balance.js script. File>Scripts>Browse>density balance.js. You can add an extra step that records the loading of the script from your local storage.
• It's worth experimenting with different neutral points, especially from other photographs in the same roll. Load other images as a background layer and repeat these steps if you encounter dramatic shifts in white balance. Create a contact sheet to experiment with more than one photograph at once.
• At this point you will have two options to reverse the negative.

Inversion method #1 - Editing in Lightroom

• Run the "🜃 3.1. Negative inversion in PS, edit in Lr" action.

1. A flat image can also be saved for further editing in Lightroom. Deactivate every layer above "Linear (negative) > Linear (positive)", save the image. Keep the "Negative Reversal" group active as it contains a necessary LUT.
2. Open the image in Lightroom and edit to taste.
3. This method allows for the usage of every Lightroom tool instead of Photoshop layers.
4. Note that white balance editing in Lightroom won't be near as efficient as the 32 bit edits in Photoshop.

Inversion method #2 - Inverting and developing in Photoshop

• Run the "🜃 3.2. Negative inversion + edit in PS" action.

1. Adjust the exposure and gamma sliders on the “Exposure/Contrast” layer to extract the full dynamic range of the negative. For very contrasted or dense negatives, start by moving the gamma correction slider to the left to reduce contrast, then lower the exposure. You can preserve some faded blacks at this point. The black point can be restored with the Levels layer upstream.
2. Over and under-exposed parts of the negative fall outside its useful dynamic range. While it may be tempting to recover every bit of information, it is often better to clip these areas to pure black or white. Photoshop doesn't have a histogram in 32 bit mode.
3. If desired, modify the LUT in the “Print Paper Contrast” layer using the provided paper contrast LUTs to achieve lifted blacks, compressed whites, or a combination of both.
4. Set the black and white points on the “Levels” layer. The layer opacity is set to 25% by default to provide a broader operational range.
5. Adjust white balance on the “White Balance” layer using the gray point sampling tool. The layer opacity is set to 50% by default, but you can increase it for a stronger effect.
6. Adjust any other layers as needed.

NOTES

• If you encounter a message about profile mismatching, select "Use the embedded profile (instead of the working space)"

• This is related to the color management policies in Color Settings.

• To prevent the profile mismatch message, untick "Profile mismatches: Ask When Opening"

• At this point you should see these layers loaded.

Paper contrast LUTs

file	function
paper_a_fogged black and white.cube	Black levels are raised and white levels are lowered
paper_a_0% black_fogged white.cube	Black levels hit 0% and white levels are lowered
paper_a_100% white_fogged blacks.cube	White levels hit 100% and black levels are raised
paper_a_100% black and white.cube	White levels hit 100% and black levels hit 0%

4. EXPORTING FOR WEB

• For web publishing, run the "🜃 4. Convert for web delivery" action. This will flatten the image, convert th bit depth to 8 bit and the color space to sRGB.

5. Creating an XMP profile

Creating the negative conversion XMP profile to be applied to TIFF and RAW files.

• Reverse the negative in Photoshop to taste.
• Run the “🜃 5. Create negative reversal LUT REC.2020” action.
• You will be prompted to open the file "Negative Reversal LUT.png". You can add an extra step that records the loading of the HALD file from your local storage.
• Then you will be prompted to save the file with the embedded LUT. Do not overwrite the original "Negative Reversal LUT.png" file.
• Convert the resulting PNG file into a .cube 3D LUT in https://sirserch.github.io/lut-creator-js/.
• Open the negative tiff in the camera raw dialogue. Switch off HDR if selected by default.
  • ALT/OPTION click Create new preset.
  • Select the recently created LUT cube "lutCreatorJs.cube", space Rec. 2020, Min:100%; Amount:100%; Max:100%.
  • Save preset.
• This preset can be loaded on top of any TIFF file of the same scene/roll.
• To apply this preset to RAW files of the same scene/roll.
  • Make sure the raw file is developed with the same settings as the file used to extract the LUT.
  • Load the 🜃 Adobe Standard to Linear preset.
  • Load the recently created profile with the negative reversal LUT.

NOTES

• The default working RGB color space in Photoshop is sRGB. Color may be slightly altered as the conversion from 32 to 16 bit at certain steps of the process defaults the color space to sRGB, regardless of the original color space of the image. It's recommended that you change the working RGB to REC.2020 in color settings for an accurate LUT extraction.
• When applying the neg>pos profile in raw images, note that every develop panel adjustment happens before the neg>pos LUT. You will see irreconcilable color distortion if changes are made on the develop panel. Contrast and brightness adjustments can be made with curves, inside a Luminance Range mask that covers the whole luminance range. These curves will affect the image after the neg>pos conversion.