Illustration of the BioPNG algorithm. BioPNG specifies encoding methods for many types of numerical formats common to Affymetrix microarray experiments into a PNG file. Note that while Intensity and Standard Deviation data have the same storage requirements, different color channels were assigned to each part so that the files are immediately recognizable when viewed and one data file will not be mistaken for the other. Affymetrix CEL intensity data only contains one digit of precision in the decimal. In the case of normalized values, some precision may be lost in the conversion, but it is guaranteed to be less than 10-4. The purpose of the custom line is to show that the BioPNG API supports arbitrary definitions of color encoding, so that many more data types may be defined and be distinguishable from each other when viewing the images. The Gel Plot is just one example of a complex encoding scheme.