Tiles@home/ColorPallete
Currently using 24bit
At the moment, the tiles rendered by the t@h clients create 24bit color PNGs. This can result in quite large tiles of up to about 100kb per 256x256 pixel tile. In comparison Mapnik tiles, that use 8 bit colour pallet can be up to 3 - 4 times smaller (of cause this is not the only difference that effects size).
Proposal to move over to 8 bit palleted tiles
My moving over to 8 bit palleted pngs, hopefully the tiles we get on average will be about half the size of the current tiles. This should help save Disk storage on the server, bandwidth used by the server as well as the time it takes for clients to download the tiles which should give a better browsing experience.
Example tiles converted to 8bit
| Original 24 bit from the server | 256 colors with pngnq -s1 | 64 colors with pngnq -s1 -n64 | 256 colors with convert -depth 8 -colors 256 -quality 100 |
|---|---|---|---|
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| 92751 bytes | 46684 bytes 79%correct 0.68meanerr | 35883 bytes 80%correct 1.49meanerr | 43218 bytes 1.09meanerr |
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| 100806 bytes (z12/2143/1406) | 46543 bytes 79%correct 0.71meanerr | 34686 bytes 77%correct 1.35meanerr | 46893 bytes 1.21meanerr |
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| 43342 bytes (z16/34298/22503) | 19778 bytes 92%correct 0.3meanerr | 14897 bytes 86%correct 0.7meanerr | 23976 bytes 1.09meanerr |
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| 8844 bytes (z17/68608/45029) | 5134 bytes 99.7%correct 0.004meanerr | 3539 bytes 99.5%correct 0.027meanerr | 10992 bytes 0.15meanerr |
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| 22905 bytes (z17/68865/44464) | 11031 bytes 95.6%correct 0.3meanerr | 8305 bytes 87.4%correct 0.89meanerr | 11469 bytes 0.39meanerr |
Issues
People have raised the concern that using palleted data can lead to inconsistent color perception across tile boundaries, as different tiles use different pallets. If you could come up with examples showing this problem, please post these here, so that one can judge if they are significant enough to use up twice as much bandwidth and disk space, compared to the 8 bit pallet
Colors used in osm-map-features
A small perl script in the client's tools directory tries to find all colors in the osmarender rules osm-map-features-z12 to osm-map-features-z17 as well as captionless-z12 and all symbols.
tools/colormap/colormap.pl -w tile captionless
That gives the following number of occurences for the color codes (as of 2008-10-04):
| # | Color | Code | Usage |
|---|---|---|---|
| 1 | #000000 | #000000 (black) | 124 |
| 2 | #101010 | #101010 | 19 |
| 3 | #202020 | #202020 | 59 |
| 4 | #303030 | #303030 | 4 |
| 5 | #404040 | #404040 | 8 |
| 6 | #505050 | #505050 | 19 |
| 7 | #606060 | #606060 | 82 |
| 8 | #707070 | #707070 | 104 |
| 9 | #777777 | #777777 | 4 |
| 10 | #808080 | #808080 (grey) | 50 |
| 11 | #b0b0b0 | #b0b0b0 | 74 |
| 12 | #c0c0c0 | #c0c0c0 (silver) | 5 |
| 13 | #d0d0d0 | #d0d0d0 | 34 |
| 14 | #d3d3d3 | #d3d3d3 (lightgrey) | 2 |
| 15 | #e0e0e0 | #e0e0e0 | 21 |
| 16 | #f0f0f0 | #f0f0f0 | 109 |
| 17 | #f8f8f8 | #f8f8f8 | 14 |
| 18 | #ffffff | #ffffff (white) | 249 |
| 19 | #000080 | #000080 (navy) | 1 |
| 20 | #0000ff | #0000ff (blue) | 14 |
| 21 | #007fff | #007fff | 8 |
| 22 | #008000 | #008000 (green) | 5 |
| 23 | #008080 | #008080 (teal) | 1 |
| 24 | #00bcdf | #00bcdf | 4 |
| 25 | #00ff00 | #00ff00 (lime) | 1 |
| 26 | #00ffff | #00ffff (cyan) | 1 |
| 27 | #2b743f | #2b743f | 32 |
| 28 | #32cd32 | #32cd32 (limegreen) | 2 |
| 29 | #4040ff | #4040ff | 21 |
| 30 | #40ff40 | #40ff40 | 8 |
| 31 | #4d5d73 | #4d5d73 | 7 |
| 32 | #556b2f | #556b2f (darkolivegreen) | 45 |
| 33 | #6060ff | #6060ff | 10 |
| 34 | #6a5a8e | #6a5a8e | 7 |
| 35 | #6fc13d | #6fc13d | 7 |
| 36 | #6fc18e | #6fc18e | 72 |
| 37 | #7fc97f | #7fc97f | 25 |
| 38 | #800000 | #800000 (maroon) | 8 |
| 39 | #800080 | #800080 (purple) | 1 |
| 40 | #808000 | #808000 (olive) | 7 |
| 41 | #8080ff | #8080ff | 35 |
| 42 | #809bc0 | #809bc0 | 26 |
| 43 | #a0f0ff | #a0f0ff | 4 |
| 44 | #a47c41 | #a47c41 | 3 |
| 45 | #a52a2a | #a52a2a (brown) | 3 |
| 46 | #b36c4c | #b36c4c | 5 |
| 47 | #b5d6f1 | #b5d6f1 | 68 |
| 48 | #bde3cb | #bde3cb | 51 |
| 49 | #bf5bc3 | #bf5bc3 | 7 |
| 50 | #c00000 | #c00000 | 5 |
| 51 | #c7f1a3 | #c7f1a3 | 13 |
| 52 | #c95e2a | #c95e2a | 7 |
| 53 | #cdabde | #cdabde | 11 |
| 54 | #d18a6a | #d18a6a | 5 |
| 55 | #d1ead1 | #d1ead1 | 18 |
| 56 | #d4dcbd | #d4dcbd | 28 |
| 57 | #d79331 | #d79331 | 7 |
| 58 | #e3e9f1 | #e3e9f1 | 13 |
| 59 | #e46d71 | #e46d71 | 25 |
| 60 | #e5e0c2 | #e5e0c2 | 21 |
| 61 | #e9dd72 | #e9dd72 | 17 |
| 62 | #ec2d2d | #ec2d2d | 21 |
| 63 | #ecd8ff | #ecd8ff | 7 |
| 64 | #eecc55 | #eecc55 | 4 |
| 65 | #efadaa | #efadaa | 20 |
| 66 | #f2caea | #f2caea | 7 |
| 67 | #f3d6b6 | #f3d6b6 | 7 |
| 68 | #f6800a | #f6800a | 5 |
| 69 | #f6dd0a | #f6dd0a | 5 |
| 70 | #f9574b | #f9574b | 19 |
| 71 | #fcffef | #fcffef | 7 |
| 72 | #fdbf6f | #fdbf6f | 13 |
| 73 | #ff0000 | #ff0000 (red) | 26 |
| 74 | #ff00ff | #ff00ff (magenta) | 15 |
| 75 | #ff4040 | #ff4040 | 11 |
| 76 | #ffebeb | #ffebeb | 20 |
| 77 | #ffff00 | #ffff00 (yellow) | 16 |
| 78 | #ffff90 | #ffff90 | 19 |
| 79 | #ffffc0 | #ffffc0 | 20 |