Understanding Colour and Resolution in Digital Imaging

1. Colour and Resolution

2. Which is the Pink Pen?

3. Here is the Pink Pen • (Example taken from http://www.colourblindawareness.org)

4. Light and Colour

5. The Solar Cell • Converts light into electricity • The stronger the light the more electricity

6. Light Voltage Measure the Current to Measure the Light Levels

7. Light 0 3 Analogue to Digital Conversion • To store three volts we need 2 bits • 00 = 0 • 01 = 1 • 10 = 2 • 11 = 3

8. Analogue v Digital Data • How to represent 10 hours and 15.34567890 minutes?

9. Quantisation Error Our analogue source gives us The digital representation becomes

10. When Applied to an Image

11. Create an Array of Digital Detectors

12. Project the Image onto the Array

13. Using 1 bit per Pixel

14. Increase the Image Resolution

15. Increase the Colour Resolution

16. Colour Resolution and Image Resolution • Colour Resolution relates to the depth of colour the image reproduces. The more bits we use to represent a single pixel the greater the number of colours may be stored in that pixel • Colour resolution is not related to the size of the image • We could have a 1 x 1 pixel image and still have a colour resolution of 16 million colours – 24 bit colour! (Not that there would be a lot of point.) • Image resolution relates to how many pixels make up the height and width of the image per inch – dots per inch. • Image resolution is an issue when it comes to the size of the image in dpi

17. Low Image Resolution Images Don’t Re-Size Well • Both images have high colour resolution

18. Colour Representation - RGB • Combine Red Green and Blue • Also referred to as 24 bit colour • Very common in computing

19. CMYK (Cyan, Magenta, Yellow & Black) • Subtract RGB by mixing Cyan Magenta Yellow and Black • Common in printing industry and computer printers

20. The Scanner

21. Interpolation • How can a 600dpi scanner scan at 1200 dpi? Without Interpolation With Interpolation

22. Digital to Analogue Conversion • The Display Adapter / Monitor – Device Resolution • In the case of a monitor, the quality of the equipment is called the dot pitch. • The dot pitch is the distance in millimetres of dots of the same colour. • In the case of a typical monitor the dot pitch is .28, meaning there is .28 mm between the red dots (green dots or blue dots).  • The smaller the dot pitch, the higher the quality of the equipment.

23. The Output from the Graphics Card • Imagine we scanned in an A4 document at a resolution of 600 dpi. • Displayed on a monitor with a 72dpi graphics adaptor

24. Very Common in Student Work • More important when we design for mobile devices • Design for liquid layout

25. Displays with Lower Colour Resolution • Q. “How do I view a 16 million colour image 256 colour display?” • A. Dithering • A is the original unchanged image • B is 1 bit monochrome with dithering • C is 1 bit monochrome without dithering – note the loss of detail • D is 8 bit colour with dithering – note the speckled effect which is common to this process

26. Gamma Correction • Images do not display the same across different hardware platforms Becomes