prof. dr. w.-p. buchwald fachhochschule braunschweig/wolfenbüttel university of applied sciences...
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Prof. Dr. W.-P. BuchwaldFachhochschule Braunschweig/Wolfenbüttel University of Applied Sciences
ImagesOriginal
Quantized
2-dimensional sampled
Sampled and quantized
Prof. Dr. W.-P. BuchwaldFachhochschule Braunschweig/Wolfenbüttel University of Applied Sciences
RED
GREEN
BLUE
Colour
Original
Colour Separation
Eye
Computer
2-dimensional sampling
Quantising(A/D-Converter)
Storage inRAM or HD
Output(Graphic adapter
and monitor, printer)
Prof. Dr. W.-P. BuchwaldFachhochschule Braunschweig/Wolfenbüttel University of Applied Sciences
Size of Images FilesDefinition: Each sample in images is called Pixel (from picture element)
N x M N=300 pixel
M=200 pixel
here: 300x200 = 600 000 pixel
Quantisation: 8bit (256 grey levels)
File size: (N x M x 8) bit = (N x M) Byte = 600kB per colour 1.8 MByte totally
No of pixels:(per colour R,G and B)
Prof. Dr. W.-P. BuchwaldFachhochschule Braunschweig/Wolfenbüttel University of Applied Sciences
Sampling of Images
Zoneplate testpattern
Prof. Dr. W.-P. BuchwaldFachhochschule Braunschweig/Wolfenbüttel University of Applied Sciences
Subsampling of Images
Throw away every 2nd pixel
Alias
Prof. Dr. W.-P. BuchwaldFachhochschule Braunschweig/Wolfenbüttel University of Applied Sciences
Solution of the Subsampling Problem
Before subsampling: lowpass filter puts away high frequencies
(corresponds to fine structures in images)
lowpass filter subsampling
Reduction of alias!
Prof. Dr. W.-P. BuchwaldFachhochschule Braunschweig/Wolfenbüttel University of Applied Sciences
Scan 100dpiOriginal
as less pixel (resolution) as possible, because of small image size (fast download for all interested people)
Our choise: adjustment of the scanner to 100 dpi
Scan 100dpi
Example
condition:
first result:
Original
We want to put a nice scan from a map of your home country to your homepage. Title: „Hello World, here I live!“
Alias
Prof. Dr. W.-P. BuchwaldFachhochschule Braunschweig/Wolfenbüttel University of Applied Sciences
A closer look...
Original
Prof. Dr. W.-P. BuchwaldFachhochschule Braunschweig/Wolfenbüttel University of Applied Sciences
The wrong way...
Original Scan 100dpi
Prof. Dr. W.-P. BuchwaldFachhochschule Braunschweig/Wolfenbüttel University of Applied Sciences
Scan 400dpiLowpass filtered
The right way...
OriginalDirect scan 100dpi Subsampled to 100dpi
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