Image Processing

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Image Processing

Post  admin on Tue 20 Jul 2010, 8:18 am

Image processing involves reducing image sizes to save storage space and save time loading. Image sizes can be reduced using the following methods:
- Dithering
- Compression

Dithering is the process of reducing the bit depth in an image. The bit depth controls the number of possible colours for each pixel. The number of colours able to be displayed can be calculated using the formula:

2n where n is the bit depth.

So an image with a bit depth of 16 would have 216 colours, or 65,536 colours.
Dithering is usually used when colour images are printed using non-colour printers. Three examples of methods of dithering are:

- Threshold dither: converts every pixel into black or white, depending on which the pixel’s greyscale value is closest to.
- Bayer dither: uses fixed patterns of black and white pixels replacing small groups of pixels. A fast method but often produces poor results.
- Stucki dither: the most complex and slowest method which produces the best results.

Images can be compressed by removing unnecessary data from the image. There are two methods of compressing images.

- Lossless: compression that does not reduce the quality of the image. Lossless compression works by temporarily removing or replacing data in an image for storage, and then restoring this data when the image is decompressed. This avoids loss of image quality, but the file will be larger.
- Lossy: compression that reduces the quality of an image. Lossy compression works by permanently removing or replacing data in an image for storage, restoring the compressed
version when displayed. This results in the loss of image quality, but also results in a smaller file size. An example of lossy data compression is the JPEG file format.

Gradually increasing the amount of lossy compression applied to an image.

Morphing is an animation technique where the pixels of an image are changed, one by one, into a different image. For a morph to occur, starting and finishing images are required, and for a smoother morph, many frames in between. Often computers can automatically do this, increasing processing load however animators previously drew each frame of the morph.

Distorting is an animation technique where an image is gradually distorted by changing the colour or intensity of each pixel.
Video data and frame rates

Video data requires the most storage and processing capability out of all the file formats. A video is basically a series of many images each slightly different to the previous one running at a large number of frames per second. This is called the frame rate.
Frame Rate

The frame rate specifies the number of images that are shown every second. A common frame rate is 24 fps (frames per second), meaning that 24 images are shown every second. The rate needs to be fast to give the illusion of movement, where there are only actually still images. The higher the frame rate, the smoother the video will be. Since each frame is an image, most commonly of JPEG file format, a video will be considerably large


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