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update webp defaults

Dane Springmeyer 2013-10-04 12:58:35 -07:00
parent e32b0c44d7
commit dfa435a1e5
1 changed files with 4 additions and 2 deletions
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6
Image-IO.md

@ -41,7 +41,7 @@ In Mapnik >= 2.3.x by default:
- PNG output is paletted png with no greater than 256 colors (aka. `png8`)
- JPEG output uses a `quality` of 85.
- TIFF output uses `PHOTOMETRIC_RGB` and `COMPRESSION_DEFLATE`
- WEBP output uses `WEBP_HINT_GRAPH` as an `image_hint` to indicate to the encoder that the image is likely a discrete tone image (this may change in the future) and otherwise uses WEBP encoder defaults.
- WEBP output uses all WEBP encoder defaults meaning lossy compression (`lossless=0`) and a default quality of `75` (`quality=75`).
See the C++ [image_util.cpp](https://github.com/mapnik/mapnik/blob/master/src/image_util.cpp) file for definitive defaults that are set for various encoders (as this wiki page may become out of date).
@ -87,11 +87,13 @@ We support one custom option called `alpha`. If you pass `webp:alpha=false` then
We support every option in the [Advanced Encoding API](https://developers.google.com/speed/webp/docs/api#advanced_encoding_api) except `show_compressed`.
We default to all webp defaults. This means that the default encoding is `quality=75` and `lossless=0`.
The `image_hint` details (from the webp sources) are:
| value | meaning |
| ----- | ------- |
| 0 | default / `WEBP_HINT_DEFAUL` |
| 0 | default / `WEBP_HINT_DEFAULT` |
| 1 | picture / `WEBP_HINT_PICTURE` (digital picture, like portrait, inner shot) |
| 2 | photo / `WEBP_HINT_PHOTO` (outdoor photograph, with natural lighting) |
| 3 | graph / `WEBP_HINT_GRAPH` (Discrete tone image (graph, map-tile etc).) |