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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.
The Solar Cell
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
00
01
10
11
Decimal
0
1
2
3
• What do we do with a reading of 0.5?
Quantisation Error
white
Grey 1
Grey 2
0
0.3
0.4
White
White
White
0
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…
But blow it up…
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
Which means…
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.
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•
•
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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.