From Image Capture to Digital Output
In looking at this we shall consider the following…
• Quantisation.
• Quantisation Error.
• Interpolation.
• Viewing images on lower dpi equipment.
• Interpolation.
Convert light levels to voltage…
Quantisation
• Back to those zeros and ones…• If we store a single reading using 2 bits we can record
the following light levels…
Binary Decimal00 001 110 211 3
• What do we do with a reading of 0.5?
Quantisation Error
white Grey 1 Grey 20 0.3 0.4
White White White0 0 0
Quantisation Errors on the Right.
Effects of poor image resolution
Source image 1Bit Monochrome (Poor image resolution)
Increase the image resolution…
Source image 1 Bit Monochrome Image “better” resolution.
Effects of poor resolution…
A low resolution image may look ok as a postage stamp…
How to enlarge a picture and keep the quality (Interpolation)…
Stretch it out and you get …
Interpolation…
• Spreads out the pixels and then fills in the gaps – the pixels don’t get bigger…
Interpolated Enlargement…
Considering Monitor Resolution
Let’s assume we scanned the above image at 600dpi.
• Print on paper A4 (600 dpi)– Image size is…– 29 x 21 cm
• Display on a monitor (72dpi)– Image size is…– 2.45 x 1.73 m
Q. What happens if you give a student a monitor which will run at
1280 X 960?
Viewed at 800 x 600
Some tips for presenting graphics on the Web.
• Use Web friendly formats (gif, jpeg, png) not Web hostile ones (tiff, bmp)
• Make use of compression if it doesn’t effect quality.
• Watch height width and colour settings.• If you must use high quality pictures
create thumbnails.• Indicate the size of the file on any related
links.