pypng - Python Sprite Strip Image Generator

import png # pip install pypng
from math import sqrt, ceil

# Background color of the outputted strip image (RGBA bytes)
TRANSPARENT_BG = b"\x00\x00\x00\x00"

# Take the given fixed-sized PNG files, and compile
# them into a sigle rectangular image from left-to-right, top-to-bottom.
def png_images_to_strip(input_file_list, output_name=None):
    sprites_per_row = ceil(sqrt(len(input_file_list)))

    # Use the first image as the standard size and metadata to go by.
    with open(input_file_list[0], "rb") as f:
        sprite_w, sprite_h, rows, init_details = png.Reader(file=f).read()
        bytes_per_pixel = 4 if init_details["alpha"] else 3

    if init_details["greyscale"] or init_details["bitdepth"] != 8:
        raise Exception("PNG images must be 32 BPP RGBA or 24 BPP RGB")

    combined_w = sprite_w * sprites_per_row
    combined_h = sprite_h * sprites_per_row
    print("Geneating %dx%d image for %dx%d sprites..." % (combined_w, combined_h, sprite_w, sprite_h))

    # Generate entire bitmap in memory, write to it later
    combined_row = [list(TRANSPARENT_BG * combined_w) for i in range(combined_h)]

    for sprite_index, file_name in enumerate(input_file_list):
        sprite_y = sprite_index // sprites_per_row
        sprite_x = sprite_index % sprites_per_row

        with open(file_name, "rb") as f:
            r = png.Reader(file=f)
            w, h, rows, details = r.read()

            if w != sprite_w or h != sprite_h:
                raise Exception("%r does not match dimensions %dx%d." % (file_name, sprite_w, sprite_h))

            if details["alpha"] != init_details["alpha"]:
                raise Exception("Sequential PNG alpha channel does not match.")

            if details["greyscale"] != init_details["greyscale"]:
                raise Exception("Sequential PNG greyscale setting does not match.")

            if details["bitdepth"] != init_details["bitdepth"]:
                raise Exception("Sequential PNG bit depth does not match.")

            for sprite_row_index, sprite_row in enumerate(rows):
                draw_at_row = (sprite_w * sprite_y) + sprite_row_index

                start = sprite_x * sprite_w
                end = (sprite_x + 1) * sprite_w

                combined_row[draw_at_row][start * bytes_per_pixel:end * bytes_per_pixel] = sprite_row

    w = png.Writer(
        combined_w,
        combined_h,
        greyscale=init_details["greyscale"],
        alpha=init_details["alpha"],
        planes=init_details["planes"],
        bitdepth=init_details["bitdepth"]
    )

    file_name = output_name if output_name else "PNG COMBINED %dx%d.png" % (combined_w, combined_h)

    with open(file_name, "wb") as f:
        w.write(f, combined_row)

    print("Saved as %r." % file_name)

if __name__ == "__main__":
    # To use, simply pass a list of file paths into "png_images_to_strip()".
    # Optionally set the output parameter.
    # Note that all PNG 'sprites' must be the same dimensions.

    # In this use case sample, the files are individual fixed size animation frame outputs of a blender render
    # rendered to files 0001.png to 0032.png.
    png_images_to_strip(["%.4d.png" % i for i in range(1, 33)])