White Paper - Gamma Correction for Macs and PCs

May 19, 2003

Why are my FCP Productions Darker on my clients PC's?
By James Diefenderfer and Philip Hodgetts

 


No Gamma Correction
 
Gamma Correction

This is one of the most posted questions on all FCP forums. It is most often posted by new editors or editors that are providing their first production for a PC client. Full disclosure - it was one of James' first post (Aug 01) as well after he had spent a wicked week editing his first FCP production. Wicked because it was frustrating and exciting all at the same time only to end up in complete darkness about why his fabulous production was way to dark on his clients Windows based PC. After all, he had done everything correctly; selected only the best shots, previewed on a NTSC color calibrated monitor and even used FCP's broadcast safe filters.

So, what went wrong? His attempt to 'wow' his client was foiled by the Gamma Monster. Sure, we all know who that is, don't we? Nope, he did not and he is not ashamed to admit it, after all acknowledging is the first step to recover, isn't it?

James is and always will be a Mac-head and while the world in his head is a wonderful one he has had to admit that not everyone has seen the light. If he wants to continue working in the Production Industry he must continue to try to understand the difference between the two dominant platforms which brings us, finally, to what he has learned about the Gamma Monster so he can better deal with it's attempt to sabotage his productions.

Gamma

  1. Gamma is the curve that describes how the middle tones of images appear on a computer. Gamma is sometimes confused with brightness and/or contrast. Changing the value of the gamma affects the mid-tones while leaving the whites and blacks unaltered. Gamma adjustment is often used to compensate for the differences between Mac and Window video cards and displays. (Apple Computer Inc. (2001), Final Cut Pro 2 User's Manual, pg. 1371.)
  2. Images are brighter on a Macintosh computer than on a Windows machine. ... As a consequence, you need to view your images (productions) on both a Mac and Windows computer, or at least on a Mac with gamma correction On (Mac standard) and Off (Windows standard), and adjust your images brightness so it doesn't look horrible on either. (Apple Computer Inc. (2002), QuickTime for the Web, pg. 252-253.)
  3. Gamma controls how the intensity of the displayed images increases with higher values. A gamma curve describes how graphics hardware interprets luminance values to display brightness. Gamma issues occur when you're trading image files among platforms with different gammas. Looking at the same image on Mac and PC side by side, RGB=0 and Y=0 look equally black, RGB=255 and Y=255 look equally white, but at Y=127 the PC looks darker. The difference is the gamma. On most PC's, gamma is that of the CRT, and can be between 2.0 and 2.5 on different machines (with 2.2 or 2.5 considered the default in different circumstances). On Macs, the default is 1.8, although the Mac OS ColorSync control lets you change this. Mac gamma gives you a lot more detail in the whites at the expense of the blacks. This is better for print projects, but less ideal for video.(Ben Waggoner. (2002), Compression for Great Digital Video, pg. 38-39.)

Now that the easy reading is out of the way we'd like to provide several solutions to help you resolve the 'PC Gamma Issue'. However, for these solutions to work several assumptions have to be made.

  1. You have selected the best shots available to tell your story
  2. You are previewing on a NTSC color calibrated monitor
  3. You are only interested in correcting a version of your final cut for PC viewing and NOT your final cut for broadcast.

Gamma Correction Techniques using Cleaner

  1. Import the FCP sequence into Cleaner.
  2. Select the Advanced Settings for QuickTime.
  3. In the Adjust Tab
    a. Select the Gamma button to increase gamma correction. (start around 30)
    b. Select the Brightness button to increase overall brightness. (start somewhere between 10-20)
  4. Complete the rest of your compression and test on your target PC.

Gamma Correction Techniques using FCP Gamma filter

  1. Nest the sequence.
  2. Add a Gamma filter from the Image control group and set the gamma to 0.8. It is easiest to do this by entering the number directly into the numeric filed.
  3. Add a Brightness and Contrast filter from the same Image Control group and set Brightness to 5 and Contrast to 10. These are useful starting points, but they will be close.
  4. Complete the rest of your compression and test on your target PC.

Gamma Correction Techniques using Sorenson Squeeze

  1. Import your source file into Squeeze.
  2. Click on the Filter button to open the filters dialog.
  3. Click the checkmarks on for Contrast, Brightness and Gamma.
    a. Drag the Gamma slider to increase gamma correction to around 30.
    b. Drag the Brightness slider to increase overall brightness by around 10-20 depending on taste.
    c. Drag the Contrast slider to around 5-10.
  4. Complete the rest of your compression and test on your target PC.
As you can see you have a number of choices for correcting your Gamma and making sure that your Final Cut Pro productions look good on your clients PC's. However, it is important to remember that Gamma correction is only one item in the long list of pre-processing steps when you are compressing productions for PC playback.


 
copyright James Diefenderfer 2003
copyright Philip Hodgetts 2003

[Top]

All screen captures, images, and textual references are the property and trademark of their creators/owners/publishers.