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Dave Jacoby
Dave Jacoby

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Travelling Salesman Portrait - A Variation


This starts when I saw that Randy Olson found an interesting thing and built upon it.

Traveling salesman portrait in Python is where I came in. It runs through a series of steps:

  • Take an image, in this case of Boris Karloff as Frankenstein’s Monster
  • Turn it into grayscale
  • Dither it to get it to more completely black and white
  • Pull a number of randomly-chosen black pixels
  • Run a Traveling Salesman Algorithm on it to connect all the pixels
  • Draw the line and write the image

Problem is, Dave Jacoby and Python is like Charlie Brown and a kite; I can never get it to work and I end up defeated and tied to a tree. In this case, believe it’s because matplotlib doesn’t like how I am handling fonts, which is immaterial because no fonts are involved in this process.

( #VirtualEnv All The Things )

But Randy Olson didn’t dream this up himself, he adapted it from R to Python, using Fronkonstin’s Work as a base. And I have few problems with R. My main issue is that I find it hard to think in terms of R’s data arrays and such. And my ggplot2 knowledge is so cargo-cult. But I can work with the code.

#!/usr/bin/env Rscript

# to be done:
# replace the library() calls with something quieter
# make usage -i file -o file
# remove the urlfile part (?)
# use Cairo so I can batch it

# Quietly load modules
suppressPackageStartupMessages(require("methods", quietly=TRUE))
suppressPackageStartupMessages(require("imager", quietly=TRUE))
suppressPackageStartupMessages(require("dplyr", quietly=TRUE))
suppressPackageStartupMessages(require("ggplot2", quietly=TRUE))
suppressPackageStartupMessages(require("scales", quietly=TRUE))
suppressPackageStartupMessages(require("TSP", quietly=TRUE))

# Handle Command Line Arguments
# cmd -> error ('need arguments')
# cmd file -> error if ! -f file, input = file, output = 'output.jpg'
# cmd file1 file2 -> error if ! -f file1, input = file1, output = file2
args = commandArgs(trailingOnly=TRUE)
if (length(args)==0) {
  stop("At least one argument must be supplied (input file).", call.=FALSE)
} else if (length(args)==1) {
  # default output file
  args[2] = "./output.jpg"

if (!file.exists(file)) { stop ("No valid input file", call.=FALSE) }

# Load, convert to grayscale, filter image (to convert it to bw) and sample
load.image(file) %>% 
  grayscale() %>%
  threshold("45%") %>% 
  as.cimg() %>% %>% 
  sample_n(8000, weight=(1-value)) %>% 
  select(x,y) -> data

# Compute distances and solve TSP (it may take a minute)
as.TSP(dist(data)) %>% 
  solve_TSP(method = "arbitrary_insertion") %>% 
  as.integer() -> solution

# Create a dataframe with the output of TSP
data.frame(id=solution) %>% 
  mutate(order=row_number()) -> order

# Rearrange the original points according the TSP output
data %>% 
  mutate(id=row_number()) %>% 
  inner_join(order, by="id") %>% arrange(order) %>% 
  select(x,y) -> data_to_plot

# A little bit of ggplot to plot results
ggplot(data_to_plot, aes(x,y)) +
    geom_path() +

# Do you like the result? Save it! (Change the filename if you want)
ggsave(output, dpi=600, width = 4, height = 4)
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This allows me to do a thing like:

./tsp.R Frankenstein.jpg TSP-Frankenstein.png

and get this output.

My TSP Frankenstein.

And do the same with

./tsp.R headshot.jpg TSP-headshot.png

and get this

My TSP Headshot.

But I don’t like this, as you can see in the comics. I think this is because “real R users” use it as a data shell and I like to think of things as programs. I come up with similarly-formatted data (like from a database), run it through my R in batch, and come up with the output while I’m doing other things.

As that kind of user, I really want this to be

./tsp.R --input headshot.jpg --output TSP-headshot.png

with optional flags for threshold and line width. I do not know of an R equivalent of Perl’s Getopt::Long. I might have to write one, if only for my own edification.

If you have any questions or comments, I would be glad to hear it. Ask me on Twitter or make an issue on my blog repo.

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