Hi,

 

The pdf from this article explains most of the FME terms use with rasters, the _x_spacing and _y_spacing correspond to pixel size.

 

Hope this helps 

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Directly from the FME Advanced Course:

 

 

Raster Origins and Extents For an entire raster dataset, the origin point is the upper left corner (A). The extents of a raster are the lower left X and Y of the lower left cell, to the upper right X and Y of the upper right cell (B) . For individual cells, 0.0, 0.0 is the lower left corner of the cell, and 1.0, 1.0 is the upper right corner. The origin point is usually the cell centre; 0.5, 0.5 (C). This is the cell origin that FME uses.

 

 

There's a pretty picture accompanying the description too but I hope this by itself helps.

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Thanks Itay and Kathy for your answer

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