Precept 5: On assignment 2

• Ordered dither
  the "Bayer" matrix for the ordered dither is mentioned in the lecture notes of lecture 3, and is the D_4 matrix on page 520 of Hearn & Baker. The example binary has been recompiled with this matrix
• Contrast filter
  The example binary precomputes the average colour. The web page says you should precompute the average luminance. You may use either method
• Floyd-Steinberg dither
  Think of what you should do for pixels at the edge of the image, and explain why in your README. Note: because of this, your Floyd-Steinberg dithered picture will probably be slightly different from the one in the example binary
• Saturation
  Use the method as described on Paul Haeberli's page

Sharpening

Consider the encircled pixels: we're going to blur them by replacing their value with the average of the values of itself and its eight neighbours.

These averages are 3.11 for the pixel with intensity 3, and 3.67 for the pixel with intensity 4: in other words, the boundary between the area with intensity 4 and the area with intensity 3 has become smaller: the image is less sharp = blurred.

If we now extrapolate by adding the difference between the original and the blurred image to the original image, we get:
I = 3 + (3 - 3.11) = 2.89 and
I = 4 + (4 - 3.67) = 4.33
Now the difference is larger, and the image is sharper.