# `gdal raster sieve`

Added in version 3.11.

Remove small raster polygons

## Synopsis

    Usage: gdal raster sieve [OPTIONS] <INPUT> <OUTPUT>

    Remove small polygons from a raster dataset.

    Positional arguments:
      -i, --input <INPUT>                                  Input raster dataset [required]
      -o, --output <OUTPUT>                                Output raster dataset (created by algorithm) [required]

    Common Options:
      -h, --help                                           Display help message and exit
      --json-usage                                         Display usage as JSON document and exit
      --config <KEY>=<VALUE>                               Configuration option [may be repeated]
      --progress                                           Display progress bar

    Options:
      -f, --of, --format, --output-format <OUTPUT-FORMAT>  Output format
      --co, --creation-option <KEY>=<VALUE>                Creation option [may be repeated]
      --overwrite                                          Whether overwriting existing output is allowed
      --mask <MASK>                                        Use the first band of the specified file as a validity mask (all pixels with a value other than zero will be considered suitable for inclusion in polygons)
      -b, --band <BAND>                                    Input band (1-based index)
      -s, --size-threshold <SIZE-THRESHOLD>                Minimum size of polygons to keep (default: 2)
      -c, --connect-diagonal-pixels                        Consider diagonal pixels as connected

    Advanced Options:
      --oo, --open-option <KEY>=<VALUE>                    Open options [may be repeated]
      --if, --input-format <INPUT-FORMAT>                  Input formats [may be repeated]

## Description

gdal raster sieve removes raster polygons smaller than a provided threshold size (in pixels) and replaces them with the pixel value of the largest neighbour polygon.

The input dataset is read as integer data which means that floating point values are rounded to integers. Re-scaling source data may be necessary in some cases (e.g. 32-bit floating point data with min=0 and max=1).

### Standard options

-f, --of, --format, --output-format <OUTPUT-FORMAT>

  Which output raster format to use. Allowed values may be given by `gdal --formats | grep raster | grep rw | sort`

--co <NAME>=<VALUE>

  Many formats have one or more optional creation options that can be used to control particulars about the file created. For instance, the GeoTIFF driver supports creation options to control compression, and whether the file should be tiled.

  May be repeated.

  The creation options available vary by format driver, and some simple formats have no creation options at all. A list of options supported for a format can be listed with the --formats command line option but the documentation for the format is the definitive source of information on driver creation options. See Raster drivers format specific documentation for legal creation options for each format.

--overwrite

  Allow program to overwrite existing target file or dataset. Otherwise, by default, gdal errors out if the target file or dataset already exists.

-b, --band <BAND>

  Input band (1-based index)

-s, --size-threshold <SIZE-THRESHOLD>

  Minimum size of polygons to keep (default: 2)

-c, --connect-diagonal-pixels

  Consider diagonal pixels (pixels at the corners) as connected. The default behavior is to only consider pixels that are touching the edges as connected, which is the same as 4-connectivity. When this option is selected, the algorithm will also consider pixels at the corners as connected, which is the same as 8-connectivity.

--mask <MASK>

  Use the first band of the specified file as a validity mask: all pixels in the mask band with a value other than zero will be considered suitable for inclusion in polygons.

## Examples

### Example 1: Remove polygons smaller than 10 pixels from the band 2 of a raster.

    $ gdal raster sieve -b 2 -s 10 input.tif output.tif