Image File Formats Flashcards
What might we want to store in an image file?
- Pixels
- Colour palette
- Different size versions (icons)
- Transparency information
- Camera data (model,focal length etc)
- Location
How many pixels are stored in a single byte using a portable bit map (.pmb) ?
There are 8 pixels in one byte,
This is used for thresholded images, where values are either 0 or 1, hence we can use a single bit to store a pixel.
How can we vary the exposure in a camera?
Changing the aperture to let more or less light in
Changing the camera shutter, the more time the shutter is open the more light will come in
What is a side effect of changing the shutter speed?
It can cause motion blur
What effect does changing the aperture on a camera have?
A small aperture can keep the whole scene in focus
A large aperture can reduce the depth of field
What is High Dynamic Range (HDR)?
This is about being able to show a larger range of brightness in an image.
How does HDR represent a wider range of intensity levels?
It uses 12 bits per colour channel.
How many bits does a GIF use to store a single pixel?
8 bits per pixel
How is a GIF image stored?
A colour palette is stored along with the pixels in the image.
When interpreting the colour of each pixel, we look in the colour palette table to see what colour it is
How is Run Length Encoding (RLE) used in a JPEG?
It is used on the 8x8 block after the discrete cosine transform has been applied, and it has been normalised using the Quantisation table.
We use RLE in a zig-zag pattern.
How do we compress an image using JPEG?
- Split image into 8x8 blocks
- Apply the Discrete Cosine Transform
- Normalise using Quantisation Table
- Apply Run Length Encoding
