Prof. Dr. W.-P. Buchwald Fachhochschule Braunschweig/Wolfenbüttel University of Applied Sciences Images Original Quantized 2-dimensional sampled Sampled and quantized

Prof. Dr. W.-P. Buchwald Fachhochschule Braunschweig/Wolfenbüttel University of Applied Sciences RED GREEN BLUE Colour Original Colour Separation Eye Computer 2-dimensional sampling Quantising (A/D-Converter) Storage in RAM or HD Output (Graphic adapter and monitor, printer)

Prof. Dr. W.-P. Buchwald Fachhochschule Braunschweig/Wolfenbüttel University of Applied Sciences Size of Images Files Definition:Each sample in images is called Pixel (from picture element) N x M N=300 pixel M=200 pixel here: 300x200 = 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. Buchwald Fachhochschule Braunschweig/Wolfenbüttel University of Applied Sciences Sampling of Images Zoneplate testpattern

Prof. Dr. W.-P. Buchwald Fachhochschule Braunschweig/Wolfenbüttel University of Applied Sciences Subsampling of Images Throw away every 2nd pixel  Alias 

Prof. Dr. W.-P. Buchwald Fachhochschule 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 filtersubsampling Reduction of alias!

Prof. Dr. W.-P. Buchwald Fachhochschule Braunschweig/Wolfenbüttel University of Applied Sciences Scan 100dpi Original 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. Buchwald Fachhochschule Braunschweig/Wolfenbüttel University of Applied Sciences A closer look... Original

Prof. Dr. W.-P. Buchwald Fachhochschule Braunschweig/Wolfenbüttel University of Applied Sciences The wrong way... OriginalScan 100dpi

Prof. Dr. W.-P. Buchwald Fachhochschule Braunschweig/Wolfenbüttel University of Applied Sciences Scan 400dpiLowpass filtered The right way... OriginalDirect scan 100dpiSubsampled to 100dpi