Image Representation

Image Representation

1. Stored as a series of pixels

2. Most are bitmap images (e.g. photos) which are made up of lots of tiny dots called pixels

3. The colour if each pixel is represented by a binary code. The number of colours available in an image is related to the number of bits the code has.

4. Black and white images only use two colours so then need one bit for each pixel - 0 for white, 1 for black

5. Two bit images can be made up of four colours - 00, 01, 10, 11

6. Increasing colour depth and resolution increases the file size

7. The colour depth is the number of bits used for each pixel

8. Given the colour depth you can work out how many colours can be made

   • Total number of colours = 2^n (n=number of bits per pixel, or bpp)
     • 1 bit image: 2^1 = 2 colours
     • 24 bit image = 2^24 = 16777216 colours

9. Most devices use a 24 bit colour depth, with eight bits for the levels of red, green, and blue in each pixel. This colour depth can produce more colours than the human eye can see.

10. Image resolution is the number of pixels in the image. It is sometimes given as width x height. The higher the resolution, the more pixels the image is made of, so the better the quality of the image.

11. File size (in bits) = image resolution x colour depth = width x height x colour depth

12. Greater image resolution or colour depth means that there are more bits in the image. This can give a higher quality image, but a higher file size.

13. Metadata is the information stored in an image file which helps the computer recreate the image on screen from the binary data in each pixel. It usually includes the image's file format, height, width, colour depth, when it was created, who created it, file size, and resolution. Without metadata, devices would not be able to display the image on screen as intended.

14. If there is a black and white image which has 16 pixels then the full image would have a size of 16 bits or 2 bytes