In this second (and last) part we will talk about  Moire, Maze Artifacts, Noise and Sharpening Halos.

Moire and Maze Artifacts

If a scene contains areas with repetitive detail which exceeds the resolution of the camera, a wavy moire pattern can appear. Anti-alias filters reduce or eliminate moire but also reduce image sharpness. Sometimes, moire can cause the camera’s internal image processing to generate maze artifacts. Here you can see an example of moire and maze artifacts:

Moire and Maze

Noise

Each pixel in a camera sensor contains one or more light sensitive photodiodes which convert the incoming light  into an electrical signal which is processed into the color value of the pixel in the final image. If the same pixel would be exposed several times by the same amount of light, the resulting color values would not be identical but have small statistical variations, called noise.

Noise in digital images is most visible in uniform surfaces (such as blue skies and shadows) as monochromatic grain. Noise increases with temperature and it also increases with sensitivity, especially the color noise in digital compact cameras. Noise also increases as pixel size decreases, which is why digital compact cameras generate much noisier images than digital SLRs. Noise is typically more visible in the red and blue channels than in the green channel.

Noise

Sharpening Halos

Software sharpness will create an optical illusion of sharpness by making the edges more contrasty. This is however unable to create detail beyond the camera’s resolution. Normal sharpening creates cleaner edges than the original. Over sharpening makes the edges look artificially sharp. This is achieved by creating a background color external halo and an internal object color halo. Because the difference between the background and object color halos is larger than between the color of the object and the background, the edge contrast has been increased, creating the illusion of enhanced sharpness, but it also create the undesired halo. You can see it here:

Sharpening halo