All critical chunks are implemented. Most ancillary chunks are. It should be able to read back any file produced by ZPNG. Interlaced files can be read, but without progressive loading.
read-png-file (file) and read-png-datastream (stream), both return a png-state object and a
boolean to indicate if CRC was successful, which most interesting property is image-data, a two
(grayscale) or three dimensional array containing image data. Other properties are width,
height, bit-depth and colour-type. If file was loaded by read-png-file slot png-file
contains pathname used.
Dynamic variable *crc-fail-behaviour* can be set to one of :error, :warn or :no-action
(default is :error), and controls what happens on checksum failure. Error signalled is of type
png-read:crc-failure, and restart png-read:ignore-crc-failure is established.
For indexed images slot index-data contains an array with indices in pallete (stored in pallete
slot), and image-data contains decoded colors.
The library loads all files from PNG Suite , but I did not check whether it does so correctly.
Note that ancillary chunks are mostly untested. They never modify primary image data array directly,
but provide additional information in slots of png-state object. Of the ancillary chunks specified
in specification missing are: cHRM, iCCP and
sPLT. gAMA is present, but using it is responsibility of library user.
Dynamic variable *warn-missing-ancillaries* controls whether library warns on encountering unknown
ancillary chunk.
tRNS- if present, additional alpha map is stored in slottransparencygAMA- if present, image gamma is stored in slotgammasBIT- if present, the original number of significant bits is stored in slotsignificant-bitsas a property listsRGB- if present, rendering intent is stored in slotrendering-intentas a keyword symboltEXt- if present, text strings are collected in slottextual-dataas an association list of keyword and stringzTXt- if present, text strings are collected in slottextual-dataas an association list of keyword and stringiTXt- if present, text strings are collected in slottextual-dataas an association list of keyword and a list of language tag, translated keyword and translated textbKGD- if present, preferred background is stored in slotpreferred-backgroundas an array of color components (RGB), greyscale datum or palette indexhIST- if present, image histogram is stored in slotimage-histogramas an arraypHYS- if present, intended pixel size is stored in slotphysical-dimensionsas a property listtIME- if present, last modification time is stored in slotlast-modificationas an universal time