A pixel array for a high definition (HD) image sensor is disclosed. The pixel array includes a number of split pixel cells each including a first photodiode and a second photodiode that is more sensitive to incident light than the first photodiode. The first photodiode can be used to sense bright or high intensity light conditions, while the second photodiode can be used to sense low to medium intensity light conditions. In the disclosed pixel array, the sensitivity of one or more photodiodes is reduced by application of a light attenuation layer over the first photodiode of each split pixel cell. In accordance with methods of the disclosure, the light attenuation layer can be formed prior to the formation of a metal, optical isolation grid structure. This can lead to better control of the thickness and uniformity of light attenuation layer.