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Concept
Jaggies
Résumé
"Jaggies" is the informal name for artifacts in s, most frequently from aliasing, which in turn is often caused by non-linear mixing effects producing high-frequency components, or missing or poor anti-aliasing filtering prior to sampling.
Jaggies are stair-like lines that appear where there should be "smooth" straight lines or curves. For example, when a nominally straight, un-aliased line steps across one pixel either horizontally or vertically, a "dogleg" occurs halfway through the line, where it crosses the threshold from one pixel to the other.
Jaggies should not be confused with most compression artifacts, which are a different phenomenon.
Jaggies occur due to the "staircase effect". This is because a line represented in raster mode is approximated by a sequence of pixels. Jaggies can occur for a variety of reasons, the most common being that the output device (display monitor or printer) does not have enough resolution to portray a smooth line. In addition, jaggies often occur when a bit-mapped image is converted to a different resolution. This is one of the advantages that vector graphics have over bitmapped graphics – the output looks the same regardless of the resolution of the output device.
The effect of jaggies can be reduced somewhat by a graphics technique known as spatial anti-aliasing. Anti-aliasing smooths out jagged lines by surrounding the jaggies with transparent pixels to simulate the appearance of fractionally-filled pixels. The downside of anti-aliasing is that it reduces contrast – rather than sharp black/white transitions, there are shades of gray – and the resulting image is fuzzy. This is an inescapable trade-off: if the resolution is insufficient to display the desired detail, the output will either be jagged or fuzzy, or some combination thereof.
In addition, jaggies often occur when a bit mapped image is converted to a different resolution. They can occur for variety of reasons, the most common being that the output device (display monitor or printer) does not have enough resolution to portray a smooth line.
Source officielle
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