When mosaicking raster datasets, often there are overlapping areas between adjacent raster datasets. To determine the output pixel value, there are several methods that you can choose from: First, Last, Blend, Mean, Minimum, and Maximum.
First
The First method determines the pixel value from the first raster dataset in the mosaic list. The existing raster dataset is considered first.
The illustration below shows the result when there are four overlapping pixels and the First option is selected. 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.
Last
The Last method determines the pixel value from the last raster dataset that is overlapping. This is the fastest method available and also the default.
The illustration below shows the result of a mosaic where the Last option is selected. When the two rasters are being mosaicked, the overlapping values from the second raster dataset are used in the output mosaic.
Blend
The Blend method uses a distance-weighted algorithm to determine the value of overlapping pixels. 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. This method is the most computationally intensive option for mosaicking.
In the illustration below, the diagram shows two overlapping raster datasets. 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). Since the x is closer to dataset R2, the value of the R2 pixel is more heavily weighted in the output.
Mean
The Mean method determines the average pixel value from the two raster datasets that are overlapping.
The illustration below shows the result of a mosaic where the Mean option is selected and the output pixel type is Float. When the two rasters are being mosaicked, the average of the two overlapping values derives the output pixel value. If many raster datasets are overlapping, only two raster datasets are processed at one time.
If the output pixel type is Integer, then the values are rounded.
Minimum
The Minimum method determines the lower pixel value from the two raster datasets that are overlapping.
The illustration below shows the result of a mosaic where the Minimum option is selected. When the two rasters are being mosaicked, the minimum value from the two raster datasets is used in the output mosaic.
Maximum
The Maximum method determines the higher pixel value from the two raster datasets that are overlapping.
The illustration below shows the result of a mosaic where the Maximum option is selected. When the two rasters are being mosaicked, the maximum value from the two raster datasets is used in the output mosaic.
Sum
The Sum method determines the total value of all the pixels added together from the overlapping raster datasets.
The illustration below shows the result of a mosaic where the Sum option is selected. When the two rasters are being mosaicked, the sum of the pixel values from the two raster datasets is used in the output mosaic.
