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i wrote a code for image dithering in python , it is working well for some images but for some it is generating unnecessary colors in the white regions . 

#IMAGE DITHERING BASED ON Floyd-Steinberg METHOD
#author : bharath kotari
#date :18-1-2018


import cv2
import numpy as np

def set_pixel(im,x,y,new):
    im[x,y]=new

def quantize(im):
    for y in range(0,height-1):
        for x in range(1,width-1):
            old_pixel=im[x,y]
            if old_pixel<127:
                new_pixel=0
            else:
                new_pixel=255
            set_pixel(im,x,y,new_pixel)
            quant_err=old_pixel-new_pixel
            set_pixel(im,x+1,y,im[x+1,y]+quant_err*w1)
            set_pixel(im,x-1,y+1, im[x-1,y+1] +  quant_err*w2 )
            set_pixel(im,x,y+1, im[x,y+1] +  quant_err * w3 )
            set_pixel(im,x+1,y+1, im[x+1,y+1] +  quant_err * w4 )


    return im

img=cv2.imread("/home/user/Downloads/blender_images/truck.jpg")
gray=cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
img2=img.copy()
width,height,z=img.shape
w1=7/16.0
#print w1
w2=3/16.0
w3=5/16.0
w4=1/16.0
blue=img[:,:,0]
blue=quantize(blue)
green=img[:,:,1]
green=quantize(green)
red=img[:,:,2]
red=quantize(red)
gray1= quantize(gray)   

image = cv2.merge((blue, green, red))
cv2.imshow('original',img2)
cv2.imshow('merged',image)
cv2.imshow('gray',gray1)
cv2.waitKey(0)

attaching image for reference ..enter image description here how to eliminate those big dots in the top right region ..

thankYou.

Bharath Kotari
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1 Answers1

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The spots happen because of integer overflow. cv2.imread() represents image using unsigned 8 bit integer (see numpy.uint8), which have a max value of 255 and start over from zero if that value is passed. For example: 255 + 50 = 49. This happen in your code when adding in the errors.

There are several methods to avoid this. The simplest would be to make sure your values don't go over 255.

Roman Smirnov
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