Now that 2, 5 and even 8 megapixels are routine, the idea that more pixels means a better picture has stopped holding. What determines what you actually see is how well the image signal processor is tuned at each stage.

ISP work runs the length of the imaging chain: black level correction, defective pixel compensation, demosaicing, 3D noise reduction, edge enhancement, auto exposure and white balance, wide dynamic range combination, and finally colour reproduction and the gamma curve. The parameters pull against one another. Too much noise reduction flattens detail and smears moving objects. Over-sharpening produces halos and amplifies noise. Poorly blended HDR leaves faces washed out in backlight.

That is why image quality cannot be judged from a datasheet or from a demo at noon on a clear day. More informative tests are noise and detail retention at low light, clarity of a face in backlight, highlight control under strong light, and smearing and bitrate fluctuation in scenes with movement.

For a manufacturer, ISP tuning is an accumulated capability that no single firmware release can conjure up. For a buyer, writing "compare both cameras in the same scene" into the procurement process is more effective than comparing specification tables.