Dithering Flashcards
What is halftoning in the print industry?
Using different sized black circles to give the impression of tones
What intensity level can be displayed on nxn pixels (on a bi-level display)?
n^2 + 1
What is the pattern number equation?
p = min(floor(I*(n^2+1)), n^2)
I = scaled intensity
What is the rough algorithm for pattern Dithering?
- get total scaled intensity
- Find pattern template to use
- Compare with nxn template
- Set pixel white if p > template number
What is the process of Ordered Dither?
-Get the pattern number for each pixel
-If pattern number is >= template number, set pixel to white
What is thresholding?
The process of turning a coloured image into a black and white image.
How does thresholding work?
Goes through every pixel and checks if it’s higher or lower than the threshold, if it’s lower set it to white else set it to black
What is the total intensity of an image?
Sum of each pixel colour intensity
What is the average intensity of an image?
The average of the total intensity
What is the error total?
The difference between the total intensity of the original image and new image
How does Floyd-Steinberg Error diffusion dithering work compared to normal error diffusion dithering?
Instead of passing 100% of the error to the next pixel, distribute it to the 4 “un-displayed” neighbours of the current pixel.
How do you get the total scaled intensity of an image?
- Calculate the total intensity
- Calculate the average intensity
- Total scaled intensity = average intensity/255
What is the advantage of thresholding?
Very fast to compute and easy to implement
What is the disadvantage of thresholding?
Very inaccurate
What is the advantage of error diffusion dithering over thresholding?
It creates a better representation of the image.
What is the disadvantage of error diffusion dithering?
There are more accurate techniques such as Floyd-Steinberg.
What does the Floyd Steinberg dithering do with the error value?
Error is retained in a local area by distributing it to its neighbours
