How do you completely disable adaptive brightness on Windows 8?

So I know nothing about your computer..and I don't know if you are still having problems.  I had the same problem, my computer would dim every time I would go to a darker image.  I was getting so frustrated with no solutions anywhere.  

Well anyways, I found the answer for me was to to into the Intel Graphics and Media Settings. Under Power there is a setting for on battery.  That was set to Display Power Saving Technology.  I just unclicked that and now my computer doesn't dim anymore.

It's crazy all the places on Windows that controls a power and brightness setting.  I found this after days and days of searching.

Your Intel graphics chip is probably the culprit, a setting called "Adaptive Contrast Enhancement"

1. Search for and launch "Intel Graphics and Media Control Panel"
2. Click Advanced and click OK
3. Media -> Image Enhancement
4. Uncheck "Adaptive Contrast Enhancement" and "Film Mode Detection" then click apply

That should fix your problem.

If your problem is with the brightness on your laptop changing randomly when "Adaptive brightness" is disabled, here's the solution: 

1. Launch "Power Options"
2. Cover your light sensor (small lens somewhere near the keyboard)
3. Wait for your screen to dim
4. Drag the "Screen brightness" slider all the way to the right while still covering the sensor
5. Uncover the sensor

That seems to reset your brightness to max regardless of if the sensor is covered.

Darren