To reduce power consumption and improve image quality including contrast ratio and color gamut, LED backlight units (BLUs) consisting of many small blocks in 2-dimensional space are implemented. Either white-gray-level luminance or color is controlled by the local dimming LED BLU. However, such a BLU can induce various recognizable artifacts. A method is proposed for exact block luminance calculation along with a new algorithm to correct local dimming artifacts. A new concept of color classes has also been developed to achieve extremely wide color gamut and to minimize color related artifacts.