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 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…

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.

• 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.