Image sensor is nothing but a electronic chip in a camera. (CCD -Charged Couple Device and CMOS- Complementary Metal–Oxide Semiconductor).
Pixels are just refers the size of the images. But when it comes to quality and professional standards you need to concern about the sensors size, sharpness and image details. Mobile phone cameras are producing larger size images but the quality of the images are considerably very low which cannot reproduce or editable.
CCD: Charged Couple Device has 4 layers in its own.
- Hot Mirror (to filter infra-red rays)
- Color Filter
Basically CCD chip needs more power to produce an image but the quality is much better with fine details.
CMOS (Complimentary Metal-Oxide Semiconductor): Basically semiconductor won't take much power but the quality of the image bit lower than a CCD. But today's advance cameras are rectify those issue and produce the better image quality.