Gamma & Density Co. Color Charts - Log Chart System
Gamma & Density Co. Log Chart System
About the Log Chart System:
The Gamma & Density Co. Log Chart System is a modular and customizable chart system to provide cinematographers with a benchmark for color and exposure, while providing crucial information to DITs and Post-Production about how the Log or RAW images should be interpreted.
Similar to the ways a film negative can be processed and interpreted, the digital image is also subject to processing and interpretation through easily accessible tools. Color charts, from the beginning, have been a method of communication between the Cinematographer and Post-Production (telecine, editorial, DI, etc.). This communication helped to ensure the creative intentions of the Cinematographer is present on footage for dailies and into the final color grade.
As new digital cameras change the way footage is captured, digital cinematography is no longer “what you see, is what you get”. The image seen on monitors during production is rarely the same image that is being captured. This influx of images captured with Log Gamma Curves and RAW capture create new possibilities for image interpretation, and further reinforce the necessity for a consistent color and exposure benchmark from which DITs and other members of post-production can realize the creative intentions of the Cinematographer.
About the Gamma & Density Co. Log Chart System:
The Gamma & Density Co. Log Chart System consists of three elements:
Log Strips are available for the following Camera formats:
The Gamma & Density Co. Log Chart System - in action:
Original Alexa Log-C Image of Gamma & Density Log Chart
- Roll Over Image to see Rec.709 Conversion -
How it works:
Using waveform percentage values provided on the Log Accessory Strip to normally expose the camera original Log-C gamma footage - users can create a Look-Up-Table (LUT) which transforms the footage into a standard linear "Rec.709" look.
Scene with Custom LUT Applied - using same conversion LUT applied to GD Log Chart
- Roll Over Image to see Rec.709 Conversion -
Frequently asked questions about THE Log Chart System:
Shooting a color chart during production (with film or digital) – either at the head of each scene, camera roll, lighting setup, visual look or in camera prep – assists DITs and Post-Production to understand how the digital image is meant to be interpreted in terms of exposure and color information.
With this information, DITs on-set can begin to create a LUT (Look-Up Table), which is a digital file containing image manipulation data. The LUT can serve many purposes, either technical (matching monitors, creating color space simulations, etc) or aesthetic (designing creative look management, “normalizing” footage for dailies, etc). On-set and during dailies creation, that LUT can be applied to a batch of clips to ensure that all the clips in that batch are processed the same way.
For more information, read the Log Chart User Guide.
Information gathered for the Log Data Strips was done using camera manufacturer recommended settings to maximize captured dynamic range. For information about recommended ISO (EI), check informational material from your camera manufacturer. Sony F65, F5 and F55 utilize ISO in a different manner than other camera systems in order to maximize the dynamic range in RAW capture. For this reason, the Log Data Strips for Sony cameras must be set to the printed ISO value on the strip in order to insure consistent results when shooting Slog2 or 3 with RAW and/or Compressed capture.
To ensure consistent color results, it is important to match the white balance on camera with the color temperature of the lights used to illuminate the chart. The best way to accomplish this is by using a color temperature meter. When determining normal exposure, it is important that all camera settings match the incident and/or reflected light meter (shutter speed, shutter angle, ISO, etc.)
For more detailed information about how to properly light and shoot a color chart, read the Log Chart User Guide.
To convert mV values to IRE / Percentage values, use the Gamma & Density Universal Exposure Table for reference.
The Base Log Chart and Accessory Strips use consumer grade matched magnets to attach the strips to the chart. The magnets create a very small magnetic field and are safe to use in reasonable proximity to other electronics components. The chart and strips have been tested side-by-side with camera media, and the magnetic field created no ill-effects.
The Log Strips will help to normalize the exposure (contrast) difference between different log gamma formats, however, it will not be able to perfectly match color discrepancies between camera formats. Each camera manufacturer has their own unique color science and method for reproducing colors. The chart will help provided a common color reference with the Rec.709 strip, but for perfectly matching color balance between cameras, users will have to employ sophisticated secondary color corrections and transform LUTs to compensate for the different color sciences.
Have a question about the Log Chart System? Contact Us!