CompuPhase build up much experience in the field of computer graphics, both 2-dimensional and 3-dimensional. A few of the papers that we wrote were published as magazine articles, others are available on this site.
- Colour metric
An introduction to colour models and specifying the distance (or closeness) of colours. Measuring the difference between colours is essential for a variety of tasks: from palette mapping to lossy image compression (and broadcast television). The document describes different approaches to the problem (CIE LUV, YIQ and YUV) and proposes a new formula for colour distances (both simpler and more accurate).
The paper also briefly covers gamma correction and its implications for transferring pictures from the Apple Macintosh to the IBM PC.
Most recent update: extra references of proposed modification to the CIE L*u*v* colour space.
- Display Typography
This article focuses on the design of "screen" fonts; fonts that are designed to be optimally legible on computer displays.
- Feathering a mask for anti-aliased sprites
Two algorithms, one conventional and one novel, to "blur" a mask on the inside. This allows a sprite engine to use the same "alpha blending" techniques for animated objects as advanced paint programs.
Most recent update: a clarification of the requirements for the convolution filters.
- Drawing the Hilbert curve
The Hilbert curve is a space filling curve that visits every point in a square grid. It has advantages in those image processing (and rendering) operations where the coherence between neighbouring pixels is important. The Hilbert curve has been applied successfully in image compression and dithering algorithms.
- Riemersma dither
Dithering along a Hilbert curve with restricted error proliferation. This paper proposes a new dither algorithm that combines the advantages of ordered dither and error diffusion dither.
- Axonometric projections
Isometric projections are used in a few popular computer games. This paper starts with an overview and a historic perspective, then focuses on six alternative isometric and dimetric projections. Although intended as an overview, the paper presents several formulae and details that are probably published here for the first time.
Most recent update: A link to the CARTESIO program was corrected (again).
- Panoramic image projection
Panoramic images are best known from QuickTime VR (QTVR). This paper gives an overview of panoramic imaging and derives the basic formulae for the projection.
This paper is in Adobe Acrobat (PDF) format, as HTML is inadequate for displaying equations. If you have trouble viewing it, please contact us.
- Quick image scaling by 2
Down-scaling by two is a simple matter of applying a "box-filter". For the purpose of up-scaling by a factor of 2, the article proposes a novel directionally-interpolating algorithm. The algorithm is quick (single pass), keeps smooth areas smooth and edges sharp.
- Quick colour averaging
Computing the middle colour between two colours is not difficult. Doing it fast requires a few tricks. Calculating the average colour is a requirement of some of the scaling and image re-sampling techniques that will be published in the near future (both on this site and in magazine articles).