pilutil.py

"""
A collection of image utilities using the Python Imaging Library (PIL).

Note that PIL is not a dependency of SciPy and this module is not
available on systems that don't have PIL installed.

"""
from __future__ import division, print_function, absolute_import

# Functions which need the PIL

import numpy
import tempfile

from numpy import (amin, amax, ravel, asarray, cast, arange, ones, newaxis,
                   transpose, iscomplexobj, uint8, issubdtype, array)

try:
    from PIL import Image, ImageFilter
except ImportError:
    import Image
    import ImageFilter


if not hasattr(Image, 'frombytes'):
    Image.frombytes = Image.fromstring

__all__ = ['fromimage', 'toimage', 'imsave', 'imread', 'bytescale',
           'imrotate', 'imresize', 'imshow', 'imfilter']


# Returns a byte-scaled image
def bytescale(data, cmin=None, cmax=None, high=255, low=0):
    """
    Byte scales an array (image).

    Byte scaling means converting the input image to uint8 dtype and scaling
    the range to ``(low, high)`` (default 0-255).
    If the input image already has dtype uint8, no scaling is done.

    Parameters
    ----------
    data : ndarray
        PIL image data array.
    cmin : scalar, optional
        Bias scaling of small values. Default is ``data.min()``.
    cmax : scalar, optional
        Bias scaling of large values. Default is ``data.max()``.
    high : scalar, optional
        Scale max value to `high`.  Default is 255.
    low : scalar, optional
        Scale min value to `low`.  Default is 0.

    Returns
    -------
    img_array : uint8 ndarray
        The byte-scaled array.

    Examples
    --------
    >>> img = array([[ 91.06794177,   3.39058326,  84.4221549 ],
                     [ 73.88003259,  80.91433048,   4.88878881],
                     [ 51.53875334,  34.45808177,  27.5873488 ]])
    >>> bytescale(img)
    array([[255,   0, 236],
           [205, 225,   4],
           [140,  90,  70]], dtype=uint8)
    >>> bytescale(img, high=200, low=100)
    array([[200, 100, 192],
           [180, 188, 102],
           [155, 135, 128]], dtype=uint8)
    >>> bytescale(img, cmin=0, cmax=255)
    array([[91,  3, 84],
           [74, 81,  5],
           [52, 34, 28]], dtype=uint8)

    """
    if data.dtype == uint8:
        return data

    if high < low:
        raise ValueError("`high` should be larger than `low`.")

    if cmin is None:
        cmin = data.min()
    if cmax is None:
        cmax = data.max()

    cscale = cmax - cmin
    if cscale < 0:
        raise ValueError("`cmax` should be larger than `cmin`.")
    elif cscale == 0:
        cscale = 1

    scale = float(high - low) / cscale
    bytedata = (data * 1.0 - cmin) * scale + 0.4999
    bytedata[bytedata > high] = high
    bytedata[bytedata < 0] = 0
    return cast[uint8](bytedata) + cast[uint8](low)


def imread(name, flatten=0):
    """
    Read an image from a file as an array.

    Parameters
    ----------
    name : str or file object
        The file name or file object to be read.
    flatten : bool, optional
        If True, flattens the color layers into a single gray-scale layer.

    Returns
    -------
    imread : ndarray
        The array obtained by reading image from file `imfile`.

    Notes
    -----
    The image is flattened by calling convert('F') on
    the resulting image object.

    """

    im = Image.open(name)
    return fromimage(im, flatten=flatten)


def imsave(name, arr, format=None):
    """
    Save an array as an image.

    Parameters
    ----------
    name : str or file object
        Output file name or file object.
    arr : ndarray, MxN or MxNx3 or MxNx4
        Array containing image values.  If the shape is ``MxN``, the array
        represents a grey-level image.  Shape ``MxNx3`` stores the red, green
        and blue bands along the last dimension.  An alpha layer may be
        included, specified as the last colour band of an ``MxNx4`` array.
    format : str
        Image format. If omitted, the format to use is determined from the
        file name extension. If a file object was used instead of a file name,
        this parameter should always be used.

    Examples
    --------
    Construct an array of gradient intensity values and save to file:

    >>> x = np.zeros((255, 255))
    >>> x = np.zeros((255, 255), dtype=np.uint8)
    >>> x[:] = np.arange(255)
    >>> imsave('/tmp/gradient.png', x)

    Construct an array with three colour bands (R, G, B) and store to file:

    >>> rgb = np.zeros((255, 255, 3), dtype=np.uint8)
    >>> rgb[..., 0] = np.arange(255)
    >>> rgb[..., 1] = 55
    >>> rgb[..., 2] = 1 - np.arange(255)
    >>> imsave('/tmp/rgb_gradient.png', rgb)

    """
    im = toimage(arr)
    if format is None:
        im.save(name)
    else:
        im.save(name, format)
    return


def fromimage(im, flatten=0):
    """
    Return a copy of a PIL image as a numpy array.

    Parameters
    ----------
    im : PIL image
        Input image.
    flatten : bool
        If true, convert the output to grey-scale.

    Returns
    -------
    fromimage : ndarray
        The different colour bands/channels are stored in the
        third dimension, such that a grey-image is MxN, an
        RGB-image MxNx3 and an RGBA-image MxNx4.

    """
    if not Image.isImageType(im):
        raise TypeError("Input is not a PIL image.")
    if flatten:
        im = im.convert('F')
    elif im.mode == '1':
        # workaround for crash in PIL, see #1613.
        im.convert('L')

    return array(im)

_errstr = "Mode is unknown or incompatible with input array shape."


def toimage(arr, high=255, low=0, cmin=None, cmax=None, pal=None,
            mode=None, channel_axis=None):
    """Takes a numpy array and returns a PIL image.

    The mode of the PIL image depends on the array shape and the `pal` and
    `mode` keywords.

    For 2-D arrays, if `pal` is a valid (N,3) byte-array giving the RGB values
    (from 0 to 255) then ``mode='P'``, otherwise ``mode='L'``, unless mode
    is given as 'F' or 'I' in which case a float and/or integer array is made.

    Notes
    -----
    For 3-D arrays, the `channel_axis` argument tells which dimension of the
    array holds the channel data.

    For 3-D arrays if one of the dimensions is 3, the mode is 'RGB'
    by default or 'YCbCr' if selected.

    The numpy array must be either 2 dimensional or 3 dimensional.

    """
    data = asarray(arr)
    if iscomplexobj(data):
        raise ValueError("Cannot convert a complex-valued array.")
    shape = list(data.shape)
    valid = len(shape) == 2 or ((len(shape) == 3) and
                                ((3 in shape) or (4 in shape)))
    if not valid:
        raise ValueError("'arr' does not have a suitable array shape for "
                         "any mode.")
    if len(shape) == 2:
        shape = (shape[1], shape[0])  # columns show up first
        if mode == 'F':
            data32 = data.astype(numpy.float32)
            image = Image.frombytes(mode, shape, data32.tostring())
            return image
        if mode in [None, 'L', 'P']:
            bytedata = bytescale(data, high=high, low=low,
                                 cmin=cmin, cmax=cmax)
            image = Image.frombytes('L', shape, bytedata.tostring())
            if pal is not None:
                image.putpalette(asarray(pal, dtype=uint8).tostring())
                # Becomes a mode='P' automagically.
            elif mode == 'P':  # default gray-scale
                pal = (arange(0, 256, 1, dtype=uint8)[:, newaxis] *
                       ones((3,), dtype=uint8)[newaxis, :])
                image.putpalette(asarray(pal, dtype=uint8).tostring())
            return image
        if mode == '1':  # high input gives threshold for 1
            bytedata = (data > high)
            image = Image.frombytes('1', shape, bytedata.tostring())
            return image
        if cmin is None:
            cmin = amin(ravel(data))
        if cmax is None:
            cmax = amax(ravel(data))
        data = (data*1.0 - cmin)*(high - low)/(cmax - cmin) + low
        if mode == 'I':
            data32 = data.astype(numpy.uint32)
            image = Image.frombytes(mode, shape, data32.tostring())
        else:
            raise ValueError(_errstr)
        return image

    # if here then 3-d array with a 3 or a 4 in the shape length.
    # Check for 3 in datacube shape --- 'RGB' or 'YCbCr'
    if channel_axis is None:
        if (3 in shape):
            ca = numpy.flatnonzero(asarray(shape) == 3)[0]
        else:
            ca = numpy.flatnonzero(asarray(shape) == 4)
            if len(ca):
                ca = ca[0]
            else:
                raise ValueError("Could not find channel dimension.")
    else:
        ca = channel_axis

    numch = shape[ca]
    if numch not in [3, 4]:
        raise ValueError("Channel axis dimension is not valid.")

    bytedata = bytescale(data, high=high, low=low, cmin=cmin, cmax=cmax)
    if ca == 2:
        strdata = bytedata.tostring()
        shape = (shape[1], shape[0])
    elif ca == 1:
        strdata = transpose(bytedata, (0, 2, 1)).tostring()
        shape = (shape[2], shape[0])
    elif ca == 0:
        strdata = transpose(bytedata, (1, 2, 0)).tostring()
        shape = (shape[2], shape[1])
    if mode is None:
        if numch == 3:
            mode = 'RGB'
        else:
            mode = 'RGBA'

    if mode not in ['RGB', 'RGBA', 'YCbCr', 'CMYK']:
        raise ValueError(_errstr)

    if mode in ['RGB', 'YCbCr']:
        if numch != 3:
            raise ValueError("Invalid array shape for mode.")
    if mode in ['RGBA', 'CMYK']:
        if numch != 4:
            raise ValueError("Invalid array shape for mode.")

    # Here we know data and mode is correct
    image = Image.frombytes(mode, shape, strdata)
    return image


def imrotate(arr, angle, interp='bilinear'):
    """
    Rotate an image counter-clockwise by angle degrees.

    Parameters
    ----------
    arr : ndarray
        Input array of image to be rotated.
    angle : float
        The angle of rotation.
    interp : str, optional
        Interpolation

        - 'nearest' :  for nearest neighbor
        - 'bilinear' : for bilinear
        - 'cubic' : cubic
        - 'bicubic' : for bicubic

    Returns
    -------
    imrotate : ndarray
        The rotated array of image.

    """
    arr = asarray(arr)
    func = {'nearest': 0, 'bilinear': 2, 'bicubic': 3, 'cubic': 3}
    im = toimage(arr)
    im = im.rotate(angle, resample=func[interp])
    return fromimage(im)


def imshow(arr):
    """
    Simple showing of an image through an external viewer.

    Uses the image viewer specified by the environment variable
    SCIPY_PIL_IMAGE_VIEWER, or if that is not defined then `see`,
    to view a temporary file generated from array data.

    Parameters
    ----------
    arr : ndarray
        Array of image data to show.

    Returns
    -------
    None

    Examples
    --------
    >>> a = np.tile(np.arange(255), (255,1))
    >>> from scipy import misc
    >>> misc.pilutil.imshow(a)

    """
    im = toimage(arr)
    fnum, fname = tempfile.mkstemp('.png')
    try:
        im.save(fname)
    except:
        raise RuntimeError("Error saving temporary image data.")

    import os
    os.close(fnum)

    cmd = os.environ.get('SCIPY_PIL_IMAGE_VIEWER', 'see')
    status = os.system("%s %s" % (cmd, fname))

    os.unlink(fname)
    if status != 0:
        raise RuntimeError('Could not execute image viewer.')


def imresize(arr, size, interp='bilinear', mode=None):
    """
    Resize an image.

    Parameters
    ----------
    arr : ndarray
        The array of image to be resized.

    size : int, float or tuple
        * int   - Percentage of current size.
        * float - Fraction of current size.
        * tuple - Size of the output image.

    interp : str, optional
        Interpolation to use for re-sizing ('nearest', 'bilinear', 'bicubic'
        or 'cubic').

    mode : str, optional
        The PIL image mode ('P', 'L', etc.) to convert `arr` before resizing.

    Returns
    -------
    imresize : ndarray
        The resized array of image.
    
    See Also
    --------
    toimage : Implicitly used to convert `arr` according to `mode`.
    scipy.ndimage.zoom : More generic implementation that does not use PIL.

    """
    im = toimage(arr, mode=mode)
    ts = type(size)
    if issubdtype(ts, int):
        percent = size / 100.0
        size = tuple((array(im.size)*percent).astype(int))
    elif issubdtype(type(size), float):
        size = tuple((array(im.size)*size).astype(int))
    else:
        size = (size[1], size[0])
    func = {'nearest': 0, 'bilinear': 2, 'bicubic': 3, 'cubic': 3}
    imnew = im.resize(size, resample=func[interp])
    return fromimage(imnew)


def imfilter(arr, ftype):
    """
    Simple filtering of an image.

    Parameters
    ----------
    arr : ndarray
        The array of Image in which the filter is to be applied.
    ftype : str
        The filter that has to be applied. Legal values are:
        'blur', 'contour', 'detail', 'edge_enhance', 'edge_enhance_more',
        'emboss', 'find_edges', 'smooth', 'smooth_more', 'sharpen'.

    Returns
    -------
    imfilter : ndarray
        The array with filter applied.

    Raises
    ------
    ValueError
        *Unknown filter type.*  If the filter you are trying
        to apply is unsupported.

    """
    _tdict = {'blur': ImageFilter.BLUR,
              'contour': ImageFilter.CONTOUR,
              'detail': ImageFilter.DETAIL,
              'edge_enhance': ImageFilter.EDGE_ENHANCE,
              'edge_enhance_more': ImageFilter.EDGE_ENHANCE_MORE,
              'emboss': ImageFilter.EMBOSS,
              'find_edges': ImageFilter.FIND_EDGES,
              'smooth': ImageFilter.SMOOTH,
              'smooth_more': ImageFilter.SMOOTH_MORE,
              'sharpen': ImageFilter.SHARPEN
              }

    im = toimage(arr)
    if ftype not in _tdict:
        raise ValueError("Unknown filter type.")
    return fromimage(im.filter(_tdict[ftype]))