Transcript PowerPoint
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. • • • • • 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.