Since the invention of color printing, the goal of color printers is to produce printouts as good as traditional color photos, which have approximately 600 pixels per inch and 256 halftone levels. In this thesis, the implementation and characterization of a digital photo printer are presented. This printer uses a microdisplay designed in the Hong Kong University of Science and Technology as the image source, and prints image of resolution 1024 by 768 spatial resolution and 24-bit color per pixel on Polaroid 500 instant film. The printout achieves a resolution of more than 300 pixels per inch and 64 halftone levels....[ Read more ]

Since the invention of color printing, the goal of color printers is to produce printouts as good as traditional color photos, which have approximately 600 pixels per inch and 256 halftone levels. In this thesis, the implementation and characterization of a digital photo printer are presented. This printer uses a microdisplay designed in the Hong Kong University of Science and Technology as the image source, and prints image of resolution 1024 by 768 spatial resolution and 24-bit color per pixel on Polaroid 500 instant film. The printout achieves a resolution of more than 300 pixels per inch and 64 halftone levels.

The printer consists of software and hardware. The software loads and decodes BMP or JPG file, and transmits image data to the photo printer hardware through the Universal Serial Bus (USB). The Field Programmable Gate Array (FPGA) on the driver board acts as the core control unit to read/write memory and outputs control signals to light source and microdisplay. Finally, the instant film is exposed with the correct image pattern loaded to the microdisplay.

A procedure for simple characterization of the photo printer is designed, and the output qualities are measured for different illumination time values. The red, green and blue illumination time values are optimized based on seven objectives, namely, uniform lightness, maximum lightness output range, uniform chroma, maximum chroma output range, uniform color, maximum color output range, and least color difference compared to CRT. Using the optimum illumination time values, the color gamut in CIE chromaticity x, y values of (0.60, 0.33) for red, (0.35, 0.49) for green and (0.20, 0.11) for blue is obtained.