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# The memory of graphics

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Detailing the various calculations that are used to estimate storage requirements of various multimedia types

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### The memory of graphics

1. 1. The Memory of GraphicsThe Memory of Graphics (Calculations involved in(Calculations involved in displaying multimedia)displaying multimedia)
2. 2. • Images place extra demands upon multimedia systems. • The current image being displayed is stored in a section of memory called the frame buffer. • Large, high resolution images may affect the performance of a multimedia presentation. • The relationship between the image on the screen and the bits in memory is called bit mapping or memory mapping.
3. 3. • The storage requirements of an image are dependent upon: • the number of pixels • the number of colours / tones • Bit depth is the number of bits required per pixel. • Each extra bit per pixel doubles the number of possible tones or colours. • [COPY Table 7.1, p.223]
4. 4. • To calculate the size of an image we must multiply the number of pixels by the bit depth. • E.g. What is the size in kilobytes of a 256 colour image displayed on a screen with a resolution of 1024 x 768 pixels. • File size = dimensions x bit depth = 1024 x 768 x 8 / 8 x 1024 = 768 Kb.
5. 5. • Video of any kind is just a series of still images that are played one after the other. • This means that to calculate the memory requirements of any video/animation we expand upon the formula we already have. • We use the file size for one image multiplied by the number of frames per second (frame rate) multiplied by how many seconds of video there is.
6. 6. • E.g. What is the file size, in gigabytes, for a 90 minute video in 32 bit colour with a resolution of 2048 x 872 being broadcast at 24 fps? • Number of frames = frame rate x seconds = 24 x 90 x 60 = 129 600 frames • Frame file size = resolution x bit depth = 2048 x 872 x 32 • Total size = 24 x 90 x 60 x 2048 x 872 x 32 / 8 x 1024 x 1024 x 1024
7. 7. • Audio files are different because of how they are displayed. • All sound must be converted from an analog to digital form. • This digitisation of sound is called sampling. • The quality of the sound is determined by its sampling rate and sample size, as well as whether the sound is mono or stereo. • The sampling rate is the number of times a slice (sample) is taken of a sound wave per second.
8. 8. • Two common sampling rates are 44.1 kHz (44100 samples per second) and 22.05 kHz (22050 samples per second). • The more samples, the better the sound. • The sample size is the number of bits per sample. • The more bits per sample, the higher the quality. • Two common bit-rates are 8 bit and 16 bit sound.
9. 9. • Stereo requires two audio streams while mono only needs one. • E.g. Calculate the file size (in Mb) of a three minute stereo audio track that has been recorded using 16 bit sound and a sampling rate of 44.1kHz. • = sample rate x sample size x time x 2 • = 44100 x 16 x 3 x 60 x 2 / 8 x 1024 x 1024
10. 10. • Stereo requires two audio streams while mono only needs one. • E.g. Calculate the file size (in Mb) of a three minute stereo audio track that has been recorded using 16 bit sound and a sampling rate of 44.1kHz. • = sample rate x sample size x time x 2 • = 44100 x 16 x 3 x 60 x 2 / 8 x 1024 x 1024