First we travel the image creating vertical lines with equal distance from each other.

First our snake travels the image creating vertical lines with equal distance from each other.

Gif showing the snake extending process:

Note: the original "The Scream" picture was not available so I used an other "The Scream" picture with similar resolution.

Note: the original "The Scream" picture was not available so I used an other "The Scream" picture with similar resolution.

Gif showing the snake extending process on the "swirl" image:

The code takes one (or more space separated) filename(s) from stdin and writes the resulting snake images to png files and prints the scores to stdout.

from PIL import Image
import numpy as np
import heapq as hq

def upd_sp(p,st):
    vs,c=0,0
    mv,mp=-1,0
    for i in range(st,gap):
        if p[1]+i<h:
            vs+=v[p[0],p[1]+i]+v[p[0]+1,p[1]+i]
            c+=2
            if vs/c>mv:
                mv=vs/c
                mp=i
    return (-mv,mp)
    
mrl=[]
bf=input().split()

for bfe in bf:
    mr,mg=0,0    
    for gap in range(40,90,1500):

        im=Image.open(bfe)
        im_d=np.asarray(im).astype(int)

        v=im_d[:,:,0]+im_d[:,:,1]+im_d[:,:,2]

        w,h=v.shape

        fp=[]
        sp=[]
        x,y=0,0
        d=1

        go=True
        while go:
            if 0<=x+2*d<w:
                fp+=[(x,y)]
                fp+=[(x+d,y)]
                sp+=[(x-(d<0),y)]
                x+=2*d
                continue
            if y+gap<h:
                for k in range(gap):
                    fp+=[(x,y+k)]
                y+=gap
                d=-d
                continue
            go=False
            
        sh=[]
        px=im.load()
        
        pl=[]

        for p in fp:
            pl+=[v[p[0],p[1]]]
            px[p[1],p[0]]=(0,127,0)   

        for p in sp:
            mv,mp=upd_sp(p,1)
            if mv<=0:
                hq.heappush(sh,(mv,1,mp+1,p))

        empty=False
        pleft=h*w//3
        pleft-=len(fp)
        while pleft>gap*2 and not empty:
            
            if len(sh)>0:
                es,eb,ee,p=hq.heappop(sh)
            else:
                empty=True
            pleft-=(ee-eb)*2
            
            mv,mp=upd_sp(p,ee)
            if mv<=0:
                hq.heappush(sh,(mv,ee,mp+1,p))    
                
            for o in range(eb,ee):
                pl+=[v[p[0],p[1]+o]]
                pl+=[v[p[0]+1,p[1]+o]]
                px[p[1]+o,p[0]]=(0,127,0)   
                px[p[1]+o,p[0]+1]=(0,127,0)

        pl+=[0]*pleft

        sb=sum(pl)/len(pl)
        ob=np.sum(v)/(h*w)

        im.save(bfe[:-4]+'snaked.png')

        if sb/ob>mr:
            mr=sb/ob
            mg=gap
            
    print(bfe,mr)
    mrl+=[mr]

print(sum(mrl)/len(mrl))