PNG Image
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PNG
- Format Type : Image
- Endian Order : Big Endian
Format Specifications
// PNG Image file format
// big endian
// header
8 bytes - signature // "89 50 4E 47 0D 0A 1A 0A" (PNG)
// chunks
num_of_chunks *
{
4 bytes (uint32) - chunk data size
4 bytes (char) - chunk type // e.g. "IHDR"
x bytes - chunk data
4 bytes - CRC
}
Critical chunks
IHDR chunk data
This chunk have to occur as the first one in the PNG file, right after header.
4 bytes (uint32) - image width
4 bytes (uint32) - image height
1 byte (uint8) - image depth // valid values are 1, 2, 4, 8, or 16
// e.g. 8bpp
1 byte (uint8) - color type // It is sum of the following values:
// 1 (palette used)
// 2 (color used)
// 4 (alpha channel used)
// Valid values are 0, 2, 3, 4, and 6.
1 byte (uint8) - compression method // "0" - deflate
// Note: deflate is mandatory for all standard PNG files
1 byte (uint8) - filther method // "0" - adaptive filtering with five basic filter types
1 byte (uint8) - interlace method // "0" - no interlace
// "1" - Adam7 interlace
PLTE chunk data
num_of_palette_entries *
{
1 byte - red color // 0-255
1 byte - green color // 0-255
1 byte - blue color // 0-255
}
This chunk is semi-optional.
Table below shows if chunk should appear for specified color type:
| Color Type | Appearence |
|---|---|
| 0 (none) | It must NOT appear |
| 2 (color used) | It can appear |
| 3 (color used and palette used) | It MUST appear |
| 4 (alpha channel used) | It must NOT appear |
| 6 (color used and alpha channel used) | It can appear |
IDAT chunk data
x bytes - image data // compressed with deflate (zlib)
IEND chunk data
// Note: This chunk is empty. // It is used only to mark the end of PNG datastream.
Ancillary chunks
tEXt chunk data
x bytes - keyword // up to 79 bytes 1 byte - null separator x bytes - text // uses ISO/IEC 8859-1 (Latin-1) character set
zTXt chunk data
x bytes - keyword // up to 79 bytes, e.g. "Raw profile type iptc" 1 byte - null separator 1 byte - compression method // "0" - deflate (zlib) x bytes - compressed text
iTXt chunk data
x bytes - keyword // up to 79 bytes 1 byte - null separator 1 byte - compression method // "0" - deflate (zlib) x bytes - language tag 1 byte - null separator x bytes - translated keyword 1 byte - null separator x bytes - text // uses UTF-8
sPLT chunk data
x bytes - palette name // up to 79 bytes
1 byte - null separator
1 byte (uint8) - sample depth // must be 8 or 16
num_of_palette_entries *
{
1-2 bytes - red color
1-2 bytes - green color
1-2 bytes - blue color
1-2 bytes - alpha
2 bytes (uint16) - frequency
}
// TODO - add more ancillary chunk descriptions
Metadata
PNG supports storing metadata information like Exif, XMP and IPTC.
Metadata can be easily edited with tools like TweakPNG, ExifTool, Exif Pilot, Exiv2 or Metadata++.
Comparsion of all editors can be found here.
Metadata can be stored in text chunks like tEXt, iTXt and zTXt.
For example GIMP saves IPTC metadata inside zTXt chunk.
Below table represents list of known metadata tags inside text chunks:
| Tag ID | Tag Name |
|---|---|
| Artist | Artist |
| Author | Author |
| Comment | Comment |
| Copyright | Copyright |
| CreationTime | CreationTime |
| Description | Description |
| Disclaimer | Disclaimer |
| Document | Document |
| Label | Label |
| Make | Make |
| Model | Model |
| Raw profile type APP1 | APP1_Profile |
| Raw profile type exif | EXIF_Profile |
| Raw profile type icc | ICC_Profile |
| Raw profile type icm | ICC_Profile |
| Raw profile type iptc | IPTC_Profile |
| Raw profile type xmp | XMP_Profile |
| Software | Software |
| Source | Source |
| TimeStamp | TimeStamp |
| Title | Title |
| URL | URL |
| Warning | PNGWarning |
| XML:com.adobe.xmp | XMP |
MultiEx BMS Script
Not written yet.
Notes and Comments
None.
Compatible Programs
- IrfanView
- GIMP
- MS Paint
Games
List of games using this file format:
- Best Friends Forever (*.PNG) (PC)
- Doki Doki Literature Club! (*.PNG) (PC)
- Hamsterball
- James Bond 007: NightFire (*.PNG) (PC)
- LBreakoutHD (*.PNG) (PC)
- LEGO Builder Bots (*.PNG) (PC)
- Lenna's Inception (*.PNG) (PC)
- Monkey Island 2: LeChuck’s Revenge (*.PNG) (PC)
- Our Life: Beginnings & Always (*.PNG) (PC)
- Ragnarok Journey
- Rigs of Rods (*.PNG) (PC)
- Styx: Shards of Darkness
- Super Mario Bros X2 / SMBX2 (*.PNG) (PC)
- SuperTuxKart (*.PNG) (PC)
- The Fall of Lazarus
- The Tribez
- Many more...
See Also
