Image File formats

Download some sample images:

Python Imaging Library (PIL)

Important raster file formats:

bmp
- Stores the color value of each bit separately
- Excellent (lossless) image quality
- Large file sizes
jpg
- Good controls for trading off image quality versus size - degree of compression can be adjusted
- 'Lossy' compression means that the original image cannot be fully recovered - information is lost
- Most commonly used for cameras and transmitted web images
- Compression works by removing changes in color that the eye is likely to ignore
- Best on images of realistic scenes with smooth color transitions
- Compressed images are smallest when color does not change perceptibly, e.g. a blue sky in the background
- Poor quality on thin lines and icons
png
- 'Lossless' data compression == small size, excellent quality
- Most popular lossless compression format on the www
- Palette-based, grayscale, full-color non-palette-based
- 1-64 bit color
- Compression is similiar to ZIP files
The above formats have the following in common:
- Specified resolution, height, and width
- Multiple color depth levels
- BMP and PNG support RGBA (RGB plus Alpha channel), JPG does not

Here is the image above at different JPG 'Quality' levels. Low Quality== more compression.