PURPOSE: To execute a pixel compression instruction in a data processing system.

CONSTITUTION: An instruction sequencer 22 transfers a graphics instruction to a graphics executing unit 29. The executing unit 29 transfers data operands in a selected number from a communication bus 36 in response to the reception of a pixel compression instruction. One of the data operands in the selected number is constituted of plural bits expressing more than one fixed decimal point values, and each fixed decimal point value expresses the intensity of one color channel in a pixel. The executing unit 29 cuts off each fixed decimal point value until the prescribed bit number, generates a corresponding cut-off bit field, and compresses the cut-off bit field at the prescribed position in a second data operand. The second data operand integrates a cut-off color channel value in a pixel format, applies an intermediate value, rotates the value, and applies the result data operand.