TFT screens have thousands of pixels, on a 1024x768 monitor, there are nearly 2.4 million cells (1024x768x3 = 2,359,296).
Having in account that figure, we realize that it is really difficult that all of them runs properly.
Death Pixel Tester arrives to your PC to check them. It will color your screen to allow you to know if it is correct or not.
It is really simple but effective, the process is easy, DPT put the screen in the basic colors (red,green,blue) and all on (white) and all off (black). Simply select a color then closely inspect your monitor in each of the primary colors checking for pixels that are not operating as expected.
From now on you will know if your TFT is ok or not.