The illustration below shows the result of a mosaic where the Mean option is selected and the output pixel type is Float. The Mean method determines the average pixel value from the two raster datasets that are overlapping. Since the x is closer to dataset R2, the value of the R2 pixel is more heavily weighted in the output. The spot where the x is located has two values: the value of the pixel in dataset R1 (outlined in red) and the value of the pixel in dataset R2 (outlined in blue). In the illustration below, the diagram shows two overlapping raster datasets. This method is the most computationally intensive option for mosaicking. The output cell value of the overlapping areas is a blend of values that overlap this blend value is determined from an algorithm that is weight based and dependent on the distance from the pixel to the edge within the overlapping area. The Blend method uses a distance-weighted algorithm to determine the value of overlapping pixels. When the two rasters are being mosaicked, the overlapping values from the second raster dataset are used in the output mosaic. The illustration below shows the result of a mosaic where the Last option is selected. This is the fastest method available and also the default. The Last method determines the pixel value from the last raster dataset that is overlapping. The values of the first raster dataset (on the left) take precedence over the next raster dataset that is mosaicked therefore, the result is the same as the first set of overlapping pixels. The illustration below shows the result when there are four overlapping pixels and the First option is selected. The existing raster dataset is considered first.
![mosaic mean mosaic mean](https://www.ancient-origins.net/sites/default/files/field/image/Ancient-Roman-Mosaics.jpg)
![mosaic mean mosaic mean](http://weknowyourdreams.com/images/mosaic/mosaic-10.jpg)
The First method determines the pixel value from the first raster dataset in the mosaic list. To determine the output pixel value, there are several methods that you can choose from: First, Last, Blend, Mean, Minimum, and Maximum. When mosaicking raster datasets, often there are overlapping areas between adjacent raster datasets.