Tile WMS vs Image WMS

Question

In OpenLayers 3, there is is ol.source.TileWMS and ol.source.ImageWMS. I don't know if this is specific to OpenLayers, but what are the trade-offs between tileWMS and imageWMS? Is there a performance difference? Other trade-offs?

Answer 1

If used with a WMS source, they're the equivalent of OpenLayers 2's singleTile parameter. As @Tim Schaub described in this letter, the TileWMS slices the map, requests a grid of images, then mosaics them together. It gives better performance, then ImageWMS (which gets the viewport in a single image), but can generate duplicates of labels (if there is a label defined in the map server's layer configuration, the server sends the label with every requested image, i.e. for every image in the grid).

TileWMS also can be used with a WMTS source.

Furthermore, TileWMS seems to be a little blurry, maybe a developer knows why.

Map with a TileWMS source:

Same map with an ImageWMS source: