One of the main novelties brought by the camera of the new iPhone 4S terminal is the implementation of an infrared filter that helps to record much better pictures, from a qualitative point of view, compared to the iPhone 4. The image above demonstrates how the infrared filter influences the quality of the images and notice that the picture on the right looks much more natural, much closer to reality than the one on the left. Practically, this filter eliminates part of the reddish tint that we see in the pictures taken with the iPhone 4 and the difference is enormous.
When IR light is allowed to pass through to the sensor, the IR light contaminates the channels (mostly the red channel) with information that was not visible in the original scene. The result is an image with a color cast. The images below show the impact of IR contamination on a scene with a dark background. The iPhone 4 image shows a reddish cast due to the extra IR light recorded on the red channel. The 4S image shows a background which much more closely resembles the original scene.
Of course, in most pictures you will not notice such a difference, but when you record pictures with objects in the immediate vicinity of the lens, you will have a difference like the one in the images. For many users, the improvement is worth switching from an iPhone 4 to an iPhone 4S, but for those who do not use the camera often, the difference will not matter much.
