Suppose one has a fairly long segment of nucleotide letters ATGC. A way to form an image, based on the Chaos Game Representation of Jeffrey, is as below. I use a pixellation level of 256x256 (2^8 x 2^8).

chars = {"A", "T", "G", "C"};
dim = 8;

makePositionsC = Compile[{{shifts, _Integer, 2}, {k, _Integer}},
   Module[{posns},
    posns = FoldList[Mod[2*#1 + #2, 2^k] &, Reverse@shifts];
    Most[Reverse[Map[{2^k, 1} + {-1, 1}*Reverse[#] &, posns]]]
    ], RuntimeOptions -> "Speed", CompilationTarget -> "C"];

replace = 
  Dispatch[Thread[chars -> {{0, 0}, {0, 1}, {1, 1}, {1, 0}}]];

FCGR[chars_, alphabet_List, k_] := Module[
  {shifts, posns, newposns},
  shifts = chars /. replace;
  newposns = Round[makePositionsC[shifts, k]];
  Normal[SparseArray[Apply[Rule, Tally[newposns], {1}], {2^k, 2^k}]]
  ]

To give some idea of what gets produced, here are pictures from the six genomes discussed in one of the articles I referenced in my earlier reply. If the images are in an array images then further processing was done to get a reasonable gray scale:

scaledimages=Map[(#/N[Max[#]])^(1/6) &, images];

References

• Jeffrey, H.: Chaos Game Representation of gene structure. Nucleic Acids Research 18(8), 2163–2170 (1990)

• Lila Kari, Kathleen A. Hill, Abu S. Sayem, Rallis Karamichalis, Nathaniel Bryans, Katelyn Davis, Nikesh S. Dattani. Mapping the Space of Genomic Signatures. http://arxiv.org/abs/1406.4105

• Rallis Karamichalis , Lila Kari , Stavros Konstantinidis and Steffen Kopecki, An investigation into inter- and intragenomic variations of graphic genomic signatures https://wolfr.am/fycQFg15

Wolfram Language code by the first listed coauthor can be found at the link below.

• Karamichalis R. Source code for computing FCGR matrices, distance matrices, MultiDimensional Scaling and separation planes. https://github.com/rallis/GenomicSignatures. Accessed 27 Jul 2016.

I use this in work that will be shown at SYNASC 2016 (Numerical Computing session 1). http://synasc.ro/2016/list-of-papers

Full details for obtaining the genome nucleotide sequences are in the code appendix (not sure when this will appear though), or see Rallis Karamichalis' web page.