How to dither an image

How to dither an image

         For editing an image with Dithering method you can specify `ThresholdDithering` or `FloydSteinbergDithering` options. The `ThresholdDitherig` is a more simple and fast dithering method, but the `FloydSteinbergDithering` is a more complex method that calculates nearest neighbors' pixels' intensity values for more smooth results. You can additionally indicate the color palette in bits for use for dithering. More bits mean a higher quality of the resulting image, but at the same time a larger image size:

from aspose.imaging import Image, RasterImage, DitheringMethod, IMultipageImage
from aspose.imaging.imageoptions import PngOptions
from aspose.pycore import as_of, is_assignable
import os


if 'TEMPLATE_DIR' in os.environ:
	templates_folder = os.environ['TEMPLATE_DIR']
else:
	templates_folder = r"C:\Users\USER\Downloads\templates"

delete_output = 'SAVE_OUTPUT' not in os.environ


def delete_file(file):
	if delete_output:
		os.remove(file)


def floyd_steinberg_dithering():
	filter_images(lambda image: image.dither(DitheringMethod.FLOYD_STEINBERG_DITHERING, 4), "floydsteinbergdithering")


def threshold_dithering():
	filter_images(lambda image: image.dither(DitheringMethod.THRESHOLD_DITHERING, 4), "thresholddithering")


def filter_images(do_filter, filter_name):
	obj_init = []
	obj_init.append("jpg")
	obj_init.append("png")
	obj_init.append("bmp")
	obj_init.append("apng")
	obj_init.append("dicom")
	obj_init.append("jp2")
	obj_init.append("j2k")
	obj_init.append("tga")
	obj_init.append("webp")
	obj_init.append("tiff")
	obj_init.append("gif")
	obj_init.append("ico")
	raster_formats = obj_init
	obj_init2 = []
	obj_init2.append("svg")
	obj_init2.append("otg")
	obj_init2.append("odg")
	obj_init2.append("eps")
	obj_init2.append("wmf")
	obj_init2.append("emf")
	obj_init2.append("wmz")
	obj_init2.append("emz")
	obj_init2.append("cmx")
	obj_init2.append("cdr")
	vector_formats = obj_init2
	all_formats = raster_formats
	all_formats.extend(vector_formats)
	
	for format_ext in all_formats:
		input_file = os.path.join(templates_folder, f"template.{format_ext}")
		is_vector_format = format_ext in vector_formats
		if is_vector_format:
			input_file = rasterize_vector_image(format_ext, input_file)

		output_file = os.path.join(templates_folder, f"{filter_name}_{format_ext}.png")
		print(format_ext)
		# explicit type casting from Image to RasterImage
		with as_of(Image.load(input_file), RasterImage) as image:
			do_filter(image)
			
			multi_page = None
			
			# if image implements an IMultipageImage interface
			if is_assignable(image, IMultipageImage):
				multi_page = as_of(image, IMultipageImage)
			
			if multi_page is not None and multi_page.page_count > 1:
				# for loop
				for_first_step = True
				page_index = 0
				for page in multi_page.pages:
					file_name = os.path.join(
						templates_folder, 
						f"{filter_name}_page{page_index}_{format_ext}.png")
					page.save(file_name, PngOptions())
					delete_file(file_name)
					page_index += 1
			else:
				image.save(output_file, PngOptions())
				delete_file(output_file)

		if is_vector_format:
			delete_file(input_file)


def rasterize_vector_image(format_ext, input_file):
	output_file = os.path.join(templates_folder, f"rasterized.{format_ext}.png")
	with Image.load(input_file) as image:
		image.save(output_file, PngOptions())

	return output_file


# run
floyd_steinberg_dithering()
threshold_dithering()