Concepts

The Python Imaging Library handles raster images, that is, rectangles of pixel data.

Bands

An image can consist of one or more bands of data. The Python Imaging Library allows you to store several bands in a single image, provided they all have the same dimensions and depth.

To get the number and names of bands in an image, use the getbands method.

Mode

The mode of an image defines the type and depth of a pixel in the image. The current release supports the following standard modes:

1 (1-bit pixels, black and white, stored as 8-bit pixels)
L (8-bit pixels, black and white)
P (8-bit pixels, mapped to any other mode using a colour palette)
RGB (3x8-bit pixels, true colour)
RGBA (4x8-bit pixels, true colour with transparency mask)
CMYK (4x8-bit pixels, colour separation)
YCbCr (3x8-bit pixels, colour video format)
I (32-bit integer pixels)
F (32-bit floating point pixels)

PIL also supports a few special modes, including RGBX (true colour with padding) and RGBa (true colour with premultiplied alpha).

You can read the mode of an image through the mode attribute. This is a string containing one of the above values.

Size

You can read the image size through the size attribute. This is a 2-tuple, containing the horizontal and vertical size in pixels.

Coordinate System

The Python Imaging Library uses a Cartesian pixel coordinate system, with (0,0) in the upper left corner. Note that the coordinates refer to the implied pixel corners; the centre of a pixel addressed as (0, 0) actually lies at (0.5, 0.5):

Coordinates are usually passed to the library as 2-tuples (x, y). Rectangles are represented as 4-tuples, with the upper left corner given first. For example, a rectangle covering all of an 800x600 pixel image is written as (0, 0, 800, 600).

Palette

The palette mode ("P") uses a colour palette to define the actual colour for each pixel.

Info

You can attach auxiliary information to an image using the info attribute. This is a dictionary object.

How such information is handled when loading and saving image files is up to the file format handler (see the chapter on Image File Formats).