- indexes colours. - makes histogram of colours in image, selects 256 most common colours, discards the rest. - pixels with other colours are converted to closest remaining colour. - Most of our maps have only a few colours. the JPG process: - software breaks image into small squares. - each square is analyzed to find pattern of colour variation. - mathematical model is found which resembles that pattern. - smaller squares or closer match gives good image but not much compression. - larger squares or weaker match gives poor image but great compression. - very poor results around sharp edges. - very good results with gradients. - good for photos, bad for most drawings. - convert vector to raster. - place drawing on an imaginary grid. - each grid cell becomes one pixel in raster image. - each grid cell crossed by a line is given the line colour. - this includes all lettering. - only effective if the grid cells are small enough. - small grid cells capture fine detail. - but many cells make large image. - trade-off between detail and file size. - converting other drawings may cause problems: - low resolution, text or fine lines hard to read. - high resolution, legible but file too big. pointers for web drawings: - use larger fonts, so still clear after conversion. - use thicker lines (not hairline). - or omit line (use transparent line around coloured shape) - avoid gradient shading. - export as GIF and JPG, see which works best. - use maximum quality settings on JPG for best results. - avoid gradients if using GIF. options: - change size. - change brightness, colours etc. - add photos or other details. - you may prefer to add photos to drawing at this stage. limitations: - many effects can't be used with indexed images. - other effects can be used but don't work as well. - change indexed colour to RGB first, in Photoshop. Source. Looking for vector maps of Germany (Deutschland Vektorkarten) for Adobe Illustrator?."

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Last Modified: April 24, 2016 @ 12:39 am