PixelBlock

Summary

Defines a group or block of pixels to include for raster processing. The PixelBlockCollection object is made up of one or more PixelBlock objects.

Discussion

The PixelBlock object defines a block of pixels within a raster to use for processing. It is used in conjunction with the PixelBlockCollection object to iterate through one or more large rasters for processing.

Syntax

PixelBlock(data, extent)

Name	Explanation	Data type
data	A NumPy array containing the pixel values for the pixel block. If the raster is not multidimensional, the shape of the array should be (rows, columns, bands). If the raster is multidimensional, the shape of the array should be (slices, rows, columns, bands).	NumPyArray
extent	The spatial extent of the pixel block.	Extent

Name

Explanation

Data type

data

A NumPy array containing the pixel values for the pixel block.

If the raster is not multidimensional, the shape of the array should be (rows, columns, bands).

If the raster is multidimensional, the shape of the array should be (slices, rows, columns, bands).

NumPyArray

extent

The spatial extent of the pixel block.

Extent

Properties

Name Explanation Data type

Name	Explanation	Data type
cell_size (Read only)	The cell size of the pixels in the pixel block. This is a tuple containing the cell size in the x-direction and the y-direction (x-size, y-size).	tuple
tlc (Read only)	The coordinates of the pixel block's upper left corner.	Point
spatial_reference (Read only)	The spatial reference of the exported image. Supported options include the following: `None` `SpatialReference` data type `ICS` or `ICS:<object_id>`, where `object_id` selects the specific raster whose image coordinate system should be used. If a value is not specified, the spatial reference of the raster dataset is used.	SpatialReference

cell_size

(Read only)

The cell size of the pixels in the pixel block. This is a tuple containing the cell size in the x-direction and the y-direction (x-size, y-size).

tuple

tlc

(Read only)

The coordinates of the pixel block's upper left corner.

Point

spatial_reference

(Read only)

The spatial reference of the exported image. Supported options include the following:

None
SpatialReference data type
ICS or ICS:<object_id>, where object_id selects the specific raster whose image coordinate system should be used.

If a value is not specified, the spatial reference of the raster dataset is used.

SpatialReference

Methods

`getData()`

Returns the NumPy array within the pixel block.

Return value

Data type	Explanation
NumPyArray	The NumPy array object from the pixel block.

Code sample

PixelBlock example

Iterates through pixel blocks to calculate the total area of forest in a land cover raster.

import arcpy

# Specify the input raster
in_raster = arcpy.Raster("landcover.tif")

# Create a PixelBlockCollection

blockCollection = arcpy.ia.PixelBlockCollection(
    in_raster, pixel_block_size = (512, 512), nodata_to_values = -1)
forest_cell_count = 0

# Iterate through each PixelBlock

try:
    while True:
        pixelblock = next(blockCollection)
        np_array = pixelblock.getData()
        forest_cell_count += np.count_nonzero(np_array == 1) # value = 1 is forest class
except StopIteration:
    pass
print("total forest pixels : " + str(forest_cell_count))