# `ImageStat` Module

The `ImageStat` module calculates global statistics for an image, or for a region of an image.

class PIL.ImageStat.Stat(image_or_list, mask=None)

  Calculate statistics for the given image. If a mask is included, only the regions covered by that mask are included in the statistics. You can also pass in a previously calculated histogram.

  Parameters:

    - image –

      A PIL image, or a precalculated histogram.

      Note

      For a PIL image, calculations rely on the `histogram()` method. The pixel counts are grouped into 256 bins, even if the image has more than 8 bits per channel. So `I` and `F` mode images have a maximum `mean`, `median` and `rms` of 255, and cannot have an `extrema` maximum of more than 255.

    - mask – An optional mask.

  extrema

    Min/max values for each band in the image.

    Note

    This relies on the `histogram()` method, and simply returns the low and high bins used. This is correct for images with 8 bits per channel, but fails for other modes such as `I` or `F`. Instead, use `getextrema()` to return per-band extrema for the image. This is more correct and efficient because, for non-8-bit modes, the histogram method uses `getextrema()` to determine the bins used.

  count

    Total number of pixels for each band in the image.

  sum

    Sum of all pixels for each band in the image.

  sum2

    Squared sum of all pixels for each band in the image.

  mean

    Average (arithmetic mean) pixel level for each band in the image.

  median

    Median pixel level for each band in the image.

  rms

    RMS (root-mean-square) for each band in the image.

  var

    Variance for each band in the image.

  stddev

    Standard deviation for each band in the image.