Fluke 225C Programming Reference Manual page 56

IDHR: Header chunk describing the image characteristics.
PLTE: Palette chunk. The first 96 entries form the color palette
table, the next 96 entries form the grey-scale palette table
for conversion to Black & White.
Notice that the index numbers in the IDAT chunk only refer
to the first 96 palette entries. To retrieve the grey-scale
values, add 96 to the index numbers.
tEXt: Text chunk specifying the acquisition date and time of the
screen. The Keyword is "Creation Time", the Text field
format is "dd-mm-yyyy,hh:mm:ss".
IDAT: The image data chunk.
IEND: The image end chunk.