What has changed in the iPhone camera, between the 4 and 4S models? A lot of things, from the manufacturer of the quality of the images, including increasing the resolution and adding an extra lens and an infrared filter. This latest novelty can be a little difficult to visualize mentally, so Camera Technica made a very nice comparison showing the difference that such a filter can make in the quality of the photographs.
By not capturing infrared light (something that can be easily tested with a mere remote control), the iPhone 4S benefits from superior accuracy when reproducing colors, especially red tones. Above, it is possible to notice the difference in the coloring of the images, being that made with the iPhone 4S much closer to reality.
The disadvantage of this infrared filter is that it can only make images only with this wavelength: there are already companies specialized in removing such a component from cameras. However, unless you have this very specific need, it shouldn't be a problem.
(via Cult of Mac)