Tag Archives: bitmap

1. Computer Systems, 3. Multimedia, Homework

Graphic file sizes calculations

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We covered this in class last week. Forrester have a good concise article on this subject

Please answer these questions

1. 600 x 300 pixels, 24 bit colour depth

2. 600 x 400, 16 bit colour depth

3. 600 x 600, 24 bit colour depth

4. An image is 6 inches by 8 inches, and has a resolution of 1200 dpi. It has a bit depth of 20.
(a) How many colours can the image store?
(b) What will be the file size of the image?

5. A photograph measures 10 inches by 7 inches, and has a resolution of 400 dpi. The number of colours each pixel can store is 65536.
(a) What is the bit depth of the image?
(b) What will be the file size of the image?

1. Computer Systems, Revision

Calculations in computer systems

I was sure I had this here already but I can’t find it.

Here are the main formula we used in the computer systems unit

  • Largest number with n bits = 2n-1
  • No of memory locations/different colours = 2n
  • Coloumn heading in a binary number at n bit =2n-1
  • Size of bitmap = no. of Horizontal pixels X no. of Vertical pixels X Colour Depth
  • No. of pixels = DPI X size in inches
  • Total storage capacity = no. of memory locations X location size.

You should also be able to convert from bits, Bytes, Kilobytes, Megabytes, Gigabytes & Terabytes.

  • Bit= 1/0 (Binary digIT)
  • 1 Byte = 8 Bits
  • 1 Kilobytes= 1024 Bytes  (210)
  • 1 Megabytes= 1024 KB  (220)
  • 1 Gigabytes = 1024 MB  (230)
  • 1 Terabytes = 1024 GB  (240)

For colour depth

  • 8 bits = 256 colours (28)
  • 16 bits = High Colour 65,536 colours (216)
  • 24 bits = True Colour 16,777,216 colours (224)
1. Computer Systems

Homework for Thursday 1st Dec

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Answer the following questions.

Convert the following to decimal

  1. 11111100 (2’s comp)
  2. 00110110
  3. 11111111 (2’s comp)

How many pixels in the following files

  1. 320×240 @ 8 bits/pixel
  2. 1024×768 @ 16 bit colour depth
  3. 1280×1024 @ 24bpp

What are the sizes of the following files in bytes

  1. 320×240 @ 8 bits/pixel
  2. 1024×768 @ 16 bit colour depth
  3. 1280×1024 @ 24bpp

Calculate the storage requirements for the following images in Megabytes (to 2 decimal places)

  1. 1440×1080 @ 24 bpp
  2. 1920×1080 @ 24 bpp
  3. 7689×4320 @ 24 bpp