Half Toning Continuous Half Toning Color Half Toning
- Slides: 74
Half Toning
Continuous Half Toning
Color Half Toning
Half toning and Colors
Digital Half Toning
Half Toning Emulating 5 different levels
Half Toning 10 levels
Original
Half Toning
Original
Dithering
Dithering and Halftoning Trade spatial for intensity resolution (works well for printing where dot printing is very high) • Thresholding. • Random dither; Robert’s algorithm • Ordered dither • Error diffusion Your eye will average over an area - Spatial Integration
Thresholding Assume we want to quantize a gray-level image to a binary colormap. Map the upper half of the gray-level scale to white, and the lower half to black – a simple threshold operation, preformed independently at each pixel.
Thresholding Original image. Simple threshold. n = 0. 5 Errors are low spatial frequencies.
Robert’s Algorithm • First add noise • Then quantize i r+1 1 Quantized to 0 r 0 x Moves errors to higher spatial frequencies. -> eye averages over an area.
Threshold
Threshold + Noise
Robert’s Algorithm Pink Blue
The trouble with noise • Difficult to compute quickly. • Not reproducible. • Pre-compute pseudo-random function and store in table. • Small tiled patterns sufficient
Dithering • It is possible to improve the quality of a quantized image by distributing the quantized error. • Let’s have a closer look.
Dithering Thresholding Dithering
Dithering Each pixel produces a quatization error The quality of the result may be improved by adjusting the threshold locally, so that adjacent pixels in small areas are quantized with different thresholds. This reduces the average local quantization error. Matrices of these threshold are called dither matrices.
Threshold + Noise
Dithering
Ordered Dithering • Trade off spatial resolution for intensity resolution. • Use dither patterns. • Can be represented as a matrix.
Other possibilities
The dithering matrix (3 x 3) 3 7 5 6 1 2 9 4 8 For all Xpixels For all Ypixels v = approximate(x, y) i = x mod 3 j = y mod 3 if v >= M[i, j] then Set_Pixel(x, y, BLACK) else Set_Pixel(x, y, WHITE)
Dithering 3 7 5 6 1 2 9 4 8 83 7 5 1 6 2 4 6 81 3 2 7 2 2 5 4 9 7 4 5 2 3 87 95 7 7 2 6 91 2 9 7 9 8 8 8 4 4 8 3 5 3 3 7 5 6 1 2 9 4 8 2 2 1 3 3 2 2 6 4 4 8 4 2 1 3 2 4 3 2 2 4 0 0 0 4 4 8 4 4 0 1 1 0 Dithering mask Image Binary image
Original
Dithering
Dithering
Error Diffusion
Floyd-Steinberg Error Diffusion With this method, the average quatization error is reduced by propagating the error from each pixel to some of its neighbors in the scan order.
1 D Error Diffusion 1 0 1
1 D Error Diffusion 1 0
1 D Error Diffusion 1 0
1 D Error Diffusion 1 0
1 D Error Diffusion 1 0 10
1 D Error Diffusion 1 0 101
1 D Error Diffusion 1 0
1 D Error Diffusion 1 0
1 D Error Diffusion 1 0
Floyd-Steinberg Error Diffusion With this method, the average quatization error is reduced by propagating the error from each pixel to some of its neighbors in the scan order. e -3 e/8 -e/4 -3 e/8 Note that the error propagation weights must sum to one
Dither vs. Floyd-Steinberg
Original Picture
Error diffusion result Dithering result
Examples – Continue
Dithering: Note that each square ring is of different brightness
Error Diffusion: Note that the error is distributed across the layers
Examples – Continue Original:
Dithering
Error Diffusion
Error Diffusion Set Acc. Err[] to zero; For each pixel in the image scanning from left to right: value= Pixel_value(x, y) + Acc. Err[x, y]; if (value > WHITE/2) { Set_pixel(x, y, WHITE); Error = value - WHITE; } else { Set_pixel(x, y, BLACK); Error = value - BLACK; } if scanning from left to right { Acc. Err[x+1, y] += 3/8 * Error; Acc. Err[x, y+1] += 3/8 * Error; Acc. Err[x+1, y+1] += 2/8 * Error; }
Space Filling Curves • order of scan
Space Filling Curves Hilbert curve (1 -4)
Space Filling Curves Hilbert curve (1 -4)
Space Filling Curves Hilbert curve (1 -4)
Space Filling Curves Hilbert curve (1 -4)
Space Filling Curves Peano curve
Context Based SFC
Original Image
Threshholding
Bayer’s Ordered Dithering
Error Diffusion
Median Cut (4 levels)
Median Cut (8 levels)
- Mary kay toning lotion before and after
- Future continuous meaning
- Without information
- The joy luck club scar
- Intracoronal direct retainers
- Mythological creature half man half horse
- What is a half horse half man called
- Half woman half snake greek mythology
- Norse mythology centaur
- Mulciber roman god
- De van clasp
- Bottom halves
- Narnia half mens half geit
- Half empty or half full
- Half playful half serious
- Continuous past tense
- Continuous past tense
- Simple past vs past perfect
- Future continuous razlaga
- Come past simple
- Future continuous future perfect exercises
- Continuous monitoring vs continuous auditing
- Continuous auditing continuous monitoring
- Past simple past continuous, past perfect examples
- Future perfect simple and future continuous exercises
- Present perfect continuous auxiliary verb
- Present past future simple present continuous exercises
- Past perfect continuous and past continuous
- Color spectrum bent into a circle
- Color groupings that provide distinct color harmonies
- Forward chaining
- Half six time
- Half lambert shading
- Half duplex vs full duplex
- Past tense ofsit
- Formula for the volume of a hemisphere
- Validità di costrutto
- Half life and doubling time
- Propofol infusion sundrome
- Strong acid-strong base titration indicator
- Heparin half life
- Heparin half life
- William howard russell charge of the light brigade
- Practice telling time by completing these sentences
- Clock showing quarter past
- Doubel angle formulas
- Half equation worksheet with answers
- Raglan's hero pattern
- Transformer utilization factor
- How to make half strength darrows
- She dwelt among the untrodden ways structure
- Revolved view
- Half section view vs full section view
- What happens when you break a magnet in half
- What is the answer?
- Difference between full wave and half wave rectifier
- Half value layer formula
- Split half method of reliability
- Split half method of reliability
- Half reaction method
- Half ionic equation
- Na to na+ half equation
- Peak voltage formula
- 175 =
- Simbol half adder
- Half life equation
- A hockey puck sliding on smooth ice at 4 m/s
- Pedigree chart and punnett square
- Half swallow boom
- Partial veneer crowns
- Aluminum foil is cut in half physical or chemical change
- Half life fluoxetine
- Redox reaction example
- Oxidized meaning
- Oxidation half reaction