ST_Histogram
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## Name

ST_Histogram — Returns a set of record summarizing a raster or raster coverage data distribution separate bin ranges. Number of bins are autocomputed if not specified.

## Synopsis

`setof record ST_Histogram(`raster rast, integer nband=1, boolean exclude_nodata_value=true, integer bins=autocomputed, double precision[] width=NULL, boolean right=false`)`;

`setof record ST_Histogram(`raster rast, integer nband, integer bins, double precision[] width=NULL, boolean right=false`)`;

`setof record ST_Histogram(`raster rast, integer nband, boolean exclude_nodata_value, integer bins, boolean right`)`;

`setof record ST_Histogram(`raster rast, integer nband, integer bins, boolean right`)`;

## Description

Returns set of records consisting of min, max, count, percent for a given raster band for each bin. If no band is specified `nband` defaults to 1.

By default only considers pixel values not equal to the `nodata` value . Set `exclude_nodata_value` to false to get count all pixels.

`width` double precision[]

  width: an array indicating the width of each category/bin. If the number of bins is greater than the number of widths, the widths are repeated.

  Example: 9 bins, widths are [a, b, c] will have the output be [a, b, c, a, b, c, a, b, c]

`bins` integer

  Number of breakouts -- this is the number of records you'll get back from the function if specified. If not specified then the number of breakouts is autocomputed.

`right` boolean

  compute the histogram from the right rather than from the left (default). This changes the criteria for evaluating a value x from [a, b) to (a, b]

Changed: 3.1.0 Removed ST_Histogram(table_name, column_name) variant.

Availability: 2.0.0

## Example: Single raster tile - compute histograms for bands 1, 2, 3 and autocompute bins

    SELECT band, (stats).*
    FROM (SELECT rid, band, ST_Histogram(rast, band) As stats
        FROM dummy_rast CROSS JOIN generate_series(1,3) As band
         WHERE rid=2) As foo;

     band |  min  |  max  | count | percent
    ------+-------+-------+-------+---------
        1 |   249 |   250 |     2 |    0.08
        1 |   250 |   251 |     2 |    0.08
        1 |   251 |   252 |     1 |    0.04
        1 |   252 |   253 |     2 |    0.08
        1 |   253 |   254 |    18 |    0.72
        2 |    78 | 113.2 |    11 |    0.44
        2 | 113.2 | 148.4 |     4 |    0.16
        2 | 148.4 | 183.6 |     4 |    0.16
        2 | 183.6 | 218.8 |     1 |    0.04
        2 | 218.8 |   254 |     5 |     0.2
        3 |    62 | 100.4 |    11 |    0.44
        3 | 100.4 | 138.8 |     5 |     0.2
        3 | 138.8 | 177.2 |     4 |    0.16
        3 | 177.2 | 215.6 |     1 |    0.04
        3 | 215.6 |   254 |     4 |    0.16

## Example: Just band 2 but for 6 bins

    SELECT (stats).*
    FROM (SELECT rid, ST_Histogram(rast, 2,6) As stats
        FROM dummy_rast
         WHERE rid=2) As foo;

        min     |    max     | count | percent
    ------------+------------+-------+---------
             78 | 107.333333 |     9 |    0.36
     107.333333 | 136.666667 |     6 |    0.24
     136.666667 |        166 |     0 |       0
            166 | 195.333333 |     4 |    0.16
     195.333333 | 224.666667 |     1 |    0.04
     224.666667 |        254 |     5 |     0.2
    (6 rows)

    -- Same as previous but we explicitly control the pixel value range of each bin.
    SELECT (stats).*
    FROM (SELECT rid, ST_Histogram(rast, 2,6,ARRAY[0.5,1,4,100,5]) As stats
        FROM dummy_rast
         WHERE rid=2) As foo;

      min  |  max  | count | percent
    -------+-------+-------+----------
        78 |  78.5 |     1 |     0.08
      78.5 |  79.5 |     1 |     0.04
      79.5 |  83.5 |     0 |        0
      83.5 | 183.5 |    17 |   0.0068
     183.5 | 188.5 |     0 |        0
     188.5 |   254 |     6 | 0.003664
    (6 rows)

## See Also

ST_Count, ST_SummaryStats, ST_SummaryStatsAgg

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