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Gamma Correction: What is it? Why is it needed?

 
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PostLink    Posted: Thu Sep 27, 2007 6:56 pm    Post subject: Gamma Correction: What is it? Why is it needed? Reply with quote

Gamma Correction: What is it? Why is it needed?


More and more home theater devices are offering gamma correction circuitry. Many of Crescendo-Systems products such as the RTC2200 Component to RGB transcoder now feature a user adjustable Gamma Correction circuit built in.

Gamma correction is an essential component to reproducing the best possible image possible. Without gamma correction, dark details (ie: shadow detail) in your projected image will lack detail or simply be missing. An adjustable gamma boost is used to restore shadow detail. If you've always found movies too dark or missing detail in dark scenes, you need a gamma boost!

So what does gamma boost actually look like?

This is best shown with real life examples of the RTC2200 in action:





So what exactly is gamma correction? What does it do? Why would I need it?
Gamma correction is a manipulation to the contrast of the display signal to correct for the fact that the intensity displayed on a CRTs and other displays is not linearly related to the input voltage. In other words: Without gamma correction, dark areas in picture will simply look too dark or black. A gamma boost corrects for this by increasing the contrast in the darker areas without affecting the overall black level of the picture.

Can't I just increase the brightness setting on my projector?
No. Your brightness setting should be set such that a true black signal looks black. If you increase your projector's brightness setting you will see more dark area detail but blacks will also look grey. Gamma correction works as it doesn't affect the low end 'true black' signal.


Before and after example of adding a non-linear gamma boost to the signal



In the real world however, it is very difficult to get a perfect flat linear response. Most responses usually end up something like we see below:



This is still considerably better than an uncompensated curve.




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