For a color managed workflow for displaying digital images on a monitor, the color profiles of the source image data as well as the display device must be known.
Images sent as SDI Signals usually conform to the Rec.709 color space. So for example the Alexa’s output can be set to Rec.709 directly or the Livegrade application converts the Log-C signal from an Alexa to a Rec.709 signal.
Reference monitors with SDI inputs usually come with their own calibration tools so that they always conform e.g. to Rec.709. When you use the HDLink devices to transform an SDI signal to HDMI, DisplayPort or DVI, you will have a monitor attached, that is most probably not calibrated to the Rec.709 color space.
For computers color management takes care about the proper transform of image data so that it is displayed properly on a certain device. So for example on Apple’s OSX the ColorSync system transforms the image before it sent to the monitor in according to the monitors characteristics. This is done by using ICC profiles to characterize image sources such as QuickTime clips as well as display devices such as monitors.
Livegrade can use the ICC profiles available for a certain monitor to do the same color management.
For more information on how to set up the ICC profiles in the device manager see the article DVI, HDMI and DisplayPort setup for Livegrade. In figure 1 you can see the color pipeline for ARRI Alexa that Livegrade sets up to apply it to images going through a HDLink box:
Figure 1: Color pipeline for Alexa with Livegrade
ICC profiles for your monitor
There are two possibilities for getting the right ICC profile for use in Livegrade. Either the ICC profile comes with the display or is downloaded from a database of such profiles (e.g. http://www.tftcentral.co.uk/articles/icc_profiles.htm ), or you create it yourself by using a color probe and a profiling software.
To give you an idea, here are the basic steps needed to create an ICC profile for example with the I1 Display Pro probe by X-Rite:
- Attach the DVI/DisplayPort/HDMI monitor that you want to use with Livegrade and HDLink later to your computer.
- Start the profiling application (e.g. the i1Profiler application that comes with the i1 Display Pro probe).
- Attach the color probe to your monitor. The probe is a small device that measures the colors displayed by the display.
- Perform the profiling. The profiling application will display a bunch of colors on the monitor, the probe will measure these colors and from this information an ICC profile is created.
- Save the resulting ICC profile for the monitor.
- Remove the monitor from your computer and attach it to the HDLink box.
- In Livegrades open the device manager and load the freshly created ICC profile for the attached monitor / HDLink.
Note: If you experience banding artifacts in the image while using ICC profiles you can limit the use of ICC profiles to display curves in the preferences. You can find more info and examples here http://kb.pomfort.com/?p=303.
The resulting color reproduction will be much closer to what you would see on a reference monitor as without the profile. Computer monitors come with all kinds of “wide gamut” and “super contrast” panels that are far away from the way smaller color space and gamut of Rec.709. Your image will in almost any case look way too saturated and crunchy without the ICC profile.
This can finally be corrected by using ICC profiles for HDMI/DisplayPort/DVI monitors with Livegrade.