JPEG Emulator

jpegemu.py

# JPEG Emulator
# licensed under GPLv2 license
#
# What this thing does?
# It emulates jpeg DCT algorithm
#
# Python 3 is required to run this code
#
# HOW TO USE:
# 1. install numpy, scipy, and Pillow package
# 2. then execute:
#    python jpegemu.py <input image> <output image> <coef size> <clip>
#
# COMMAND LINE INTERFACE:
# python jpegemu.py <input image> <output image> <coef size> <clip>
# <input image>: image to be processed
# <output image>: output to the resulting image
# <coef mul>: The quantization coefficient multiplication factor, higher means more compression
# <clip>: 'clip' or 'noclip',
#         this will limit the color value in range of [-128, 127) ('clip' option),
#         otherwise the color will not be clipped/limited ('unclip' option)

import sys
import numpy as np
import math
from PIL import Image, ImageFilter
from scipy.fftpack import dctn, idctn

qcoef = [[16,  11,  10,  16,  24, 40,  51,  61],
		 [12,  12,  14,  19,  26, 58,  60,  55],
		 [14,  13,  16,  24,  40, 57,  69,  56],
		 [14,  17,  22,  29,  51, 87,  80,  62],
		 [18,  22,  37,  56,  68, 109, 103, 77],
		 [24,  35,  55,  64,  81, 104, 113, 92],
		 [49,  64,  78,  87,  103, 121, 120, 101],
		 [72,  92,  95,  98,  112, 100, 103, 99]]

def main():
	inputfile = sys.argv[1]
	outputfile = sys.argv[2]
	coefmul = int(sys.argv[3])
	clip = sys.argv[4]

	if sys.argv[4] == 'clip':
		clip = True
	else:
		clip = False

	try:
		im = Image.open(inputfile)
		im2 = Image.new("RGB",im.size,(0,0,0))
		
	except IOError:
		print("Cannot open file ", inputfile);

	w, h = im.size
	total = w/8 * h/8
	progress = 0
	coef = np.array(qcoef) * coefmul

	for y in range(int(math.ceil(h/8))):
		for x in range(int(math.ceil(w/8))):
			idX = x*8
			idY = y*8
			parts = im.crop(box=(idX,idY,idX+8,idY+8))
			splitRGB = parts.split()
			r = np.array(list(splitRGB[0].getdata())).reshape(8,8) - 128
			g = np.array(list(splitRGB[1].getdata())).reshape(8,8) - 128 
			b = np.array(list(splitRGB[2].getdata())).reshape(8,8) - 128
			rdct = np.round(dctn(r,norm="ortho") / coef) * coef
			gdct = np.round(dctn(g,norm="ortho") / coef) * coef
			bdct = np.round(dctn(b,norm="ortho") / coef) * coef
			if clip:
				rdct = np.clip(idctn(rdct,norm="ortho"),-128,127)
				gdct = np.clip(idctn(gdct,norm="ortho"),-128,127)
				bdct = np.clip(idctn(bdct,norm="ortho"),-128,127)
			else:
				rdct = idctn(rdct,norm="ortho")
				gdct = idctn(gdct,norm="ortho")
				bdct = idctn(bdct,norm="ortho")
			r = Image.fromarray(np.round(rdct + 128).astype(np.uint8), mode="L")
			g = Image.fromarray(np.round(gdct + 128).astype(np.uint8), mode="L")
			b = Image.fromarray(np.round(bdct + 128).astype(np.uint8), mode="L")
			im2.paste(Image.merge(mode="RGB", bands=(r,g,b)), box=(idX,idY))
			progress += 1
			sys.stdout.write("\rProgress " + str(round(100 * (progress / total))) + "%")
			sys.stdout.flush()

	im2.save(outputfile)
	im.close()

if __name__ == "__main__":
	main()