Thumbnailing helpers.

_thumbnail.py

from math import ceil

def resize_dimensions(x, y, max_width=None, max_height=None, min_side=None, max_side=None):
    if not any([max_width, max_height, min_side, max_side]):
        return x, y

    original_x, original_y = x, y

    priority_width = True
    if max_width and x > max_width:
        ratio = max_width / float(x)
        x *= ratio
        y *= ratio

    if max_height and y > max_height:
        priority_width = False
        ratio = max_height / float(y)
        y *= ratio
        x *= ratio

    biggest_side = max(x, y)
    if max_side and biggest_side > max_side:
        priority_width = x == biggest_side
        ratio = float(max_side) / biggest_side
        x *= ratio
        y *= ratio

    smallest_side = min(x, y)
    if min_side and smallest_side > min_side:
        priority_width = x == smallest_side
        ratio = float(min_side) / smallest_side
        x *= ratio
        y *= ratio

    if priority_width:
        x = round(x)
        y = ceil((x / original_x) * original_y)
    else:
        y = round(y)
        x = ceil((y / original_y) * original_x)

    return int(x), int(y)


def crop_center(width, height, target_width, target_height):
    """
    Only crops if the image is bigger than targets.
    """
    left = max(0, int(round((width - target_width) / 2.0)))
    top = max(0, int(round((height - target_height) / 2.0)))
    right = int(round((width + min(width, target_width)) / 2.0))
    bottom = int(round((height + min(height, target_height)) / 2.0))

    return left, top, right, bottom

templatetag.py

def _path_trim(abs_path, rel_path):
    cur_dir = os.path.dirname(rel_path)
    while cur_dir:
        abs_path = os.path.dirname(abs_path)
        cur_dir = os.path.dirname(cur_dir)

    return abs_path


def _get_thumbnail_path(file_name, file_path, file_url, size):
    thumb_dir = os.path.join(_path_trim(file_path, file_name), 'thumbs')
    thumb_url = os.path.join(_path_trim(file_url, file_name), 'thumbs')

    filedir, filename = os.path.split(file_name)
    basename, format = os.path.splitext(filename)
    thumb_filename = basename + '_' + size + format
    path = os.path.join(thumb_dir, filedir, thumb_filename)
    url = os.path.join(thumb_url, filedir, thumb_filename)

    return path, url


def thumbnail(file, ...):
    """
    This function is a disaster due to restrictions in Django templatetags. Removed the disasterous parts. Enter at your own peril.
    """
    time_started = time.time()

    if not os.path.exists(file.path):
        log.error("thumbnail: Original image does not exist: %s" % file.path)
        return "" # TODO: Return a placeholder URL?

    # ...

    target_path, target_url = _get_thumbnail_path(file.name, file.path, file.url, size_name)

    if os.path.exists(target_path):
        # Does the thumb already exist?
        if os.path.getmtime(file.path) <= os.path.getmtime(target_path):
            # Still valid
            return target_url

    elif not os.path.isdir(os.path.dirname(target_path)):
        # Does the directory need to be created?
        os.makedirs(os.path.dirname(target_path))

    # Get original x, y
    try:
        image = Image.open(file.path)
    except IOError, e:
        raise ValueError("Failed to open image path: %s (error: %s)" % (file.path, e))

    if image.mode == 'P':
        # Some people have uploaded jpeg images that are actually PNGs -- deal with this
        image = image.convert('RGB')

    original_x, original_y = image.size
    x, y = resize_dimensions(original_x, original_y, max_width=max_width, max_height=max_height, min_side=min_side, max_side=max_side)
    image.thumbnail([x, y], Image.ANTIALIAS)


    if crop_size:
        box = crop_center(x, y, crop_width, crop_height)
        image = image.crop(box)

    try:
        image.save(target_path, "JPEG", quality=85, optimize=True)
    except IOError:
        image.save(target_path, "JPEG", quality=85)

    time_elapsed = time.time() - time_started
    log.info("Created new thumbnail in %s seconds: %s" % (time_elapsed, target_path))

    return target_url