Uttori ImagePNG

A PNG Decoder and meta data reading utility.

Install

1npm install --save @uttori/image-png

Config

1{
2}

---

Example

1const image_data = await FileUtility.readFile('./test/assets/PngSuite', 'oi1n0g16', 'png', null);
2const image = ImagePNG.fromFile(image_data);
3image.decodePixels();
4const length = image.pixels.length;
5➜ 6144
6const pixel = image.getPixel(0, 0);
7➜ [255, 255, 255, 255]

API Reference

Classes

ImagePNG ⇐ DataBuffer

PNG Decoder

Functions

debug() : function

ImagePNG ⇐ DataBuffer

PNG Decoder

Kind: global class
Extends: DataBuffer
See

• Chunk Specifications
• The Art of PNG Glitch
• PngSuite, test-suite for PNG
• Chunk Specifications (LibPNG)
• Chunk Specifications (W3C)
• PNGs containing a chunk with length 0xffffffff
• PNG files can be animated via network latency
• TweakPNG

Properties

Name	Type	Description
width	number	Pixel Width
height	number	Pixel Height
bitDepth	number	Image Bit Depth, one of: 1, 2, 4, 8, 16
colorType	number	= Defines pixel structure, one of: 0, 2, 3, 4, 6
compressionMethod	number	Type of compression, always 0
filterMethod	number	Type of filtering, always 0
interlaceMethod	number	Type of interlacing, one of: 0, 1
colors	number	Number of bytes for each pixel
alpha	boolean	True when the image has an alpha transparency layer
palette	Array.<number> | Uint8Array	Raw Color data
pixels	Uint8Array	Raw Image Pixel data
transparency	Uint8Array	Raw Transparency data
physical	object	Object containing physical dimension information
physical.width	number	Physical Dimension Width
physical.height	number	Physical Dimension Height
physical.unit	number	Physical Dimension Units, with 0 being unknown and 1 being Meters
dataChunks	Array.<Uint8Array>	Image Data pieces
header	Uint8Array	PNG Signature from the data

• ImagePNG ⇐ DataBuffer
  • new ImagePNG(input)
  • instance
    • .width : number
    • .height : number
    • .bitDepth : number
    • .colorType : number
    • .compressionMethod : number
    • .filterMethod : number
    • .interlaceMethod : number
    • .colors : number
    • .alpha : boolean
    • .palette : Array.<number> | Uint8Array
    • .pixels : Uint8Array
    • .transparency : Uint8Array
    • .physical : object
      • .width : number
      • .height : number
      • .unit : number
    • .dataChunks : Array.<Uint8Array>
    • .header : Array | Uint8Array
    • .setBitDepth(bitDepth)
    • .setColorType(colorType)
    • .setCompressionMethod(compressionMethod)
    • .setFilterMethod(filterMethod)
    • .setInterlaceMethod(interlaceMethod)
    • .setPalette(palette)
    • .getPixel(x, y) ⇒ Array
    • .parse()
    • .decodeHeader()
    • .decodeChunk() ⇒ string
    • .decodeIHDR(chunk)
    • .decodePLTE(chunk)
    • .decodeIDAT(chunk)
    • .decodeTRNS(chunk)
    • .decodePHYS(chunk)
    • .decodeIEND(_chunk)
    • .decodePixels()
    • .interlaceNone(data)
    • .unFilterNone(scanline, bpp, offset, length)
    • .unFilterSub(scanline, bpp, offset, length)
  • static
    • .fromFile(data) ⇒ ImagePNG
    • .fromBuffer(buffer) ⇒ ImagePNG

new ImagePNG(input)

Creates a new ImagePNG.

Param	Type	Description
input	Array | ArrayBuffer | Buffer | DataBuffer | Int8Array | Int16Array | Int32Array | number | string | Uint8Array | Uint16Array | Uint32Array	The data to process.

Example (new ImagePNG(list, options))

1const image_data = await FileUtility.readFile('./test/assets/PngSuite', 'oi1n0g16', 'png', null);
2const image = ImagePNG.fromFile(image_data);
3image.decodePixels();
4const length = image.pixels.length;
5 ➜ 6144
6const pixel = image.getPixel(0, 0);
7 ➜ [255, 255, 255, 255]

imagePNG.width : number

Pixel Width

Kind: instance property of ImagePNG

imagePNG.height : number

Pixel Height

Kind: instance property of ImagePNG

imagePNG.bitDepth : number

Image Bit Depth, one of: 1, 2, 4, 8, 16

Kind: instance property of ImagePNG

imagePNG.colorType : number

Defines pixel structure, one of: 0, 2, 3, 4, 6

Kind: instance property of ImagePNG

imagePNG.compressionMethod : number

Type of compression, always 0

Kind: instance property of ImagePNG

imagePNG.filterMethod : number

Type of filtering, always 0

Kind: instance property of ImagePNG

imagePNG.interlaceMethod : number

Type of interlacing, one of: 0, 1

Kind: instance property of ImagePNG

imagePNG.colors : number

Number of bytes for each pixel

Kind: instance property of ImagePNG

imagePNG.alpha : boolean

True when the image has an alpha transparency layer

Kind: instance property of ImagePNG

imagePNG.palette : Array.<number> | Uint8Array

Raw Color data

Kind: instance property of ImagePNG

imagePNG.pixels : Uint8Array

Raw Image Pixel data

Kind: instance property of ImagePNG

imagePNG.transparency : Uint8Array

Raw Transparency data

Kind: instance property of ImagePNG

imagePNG.physical : object

physical - Object containing physical dimension information

Kind: instance property of ImagePNG

• .physical : object
  • .width : number
  • .height : number
  • .unit : number

physical.width : number

Physical Dimension Width

Kind: static property of physical

physical.height : number

Physical Dimension Height

Kind: static property of physical

physical.unit : number

Physical Dimension Units, with 0 being unknown and 1 being Meters

Kind: static property of physical

imagePNG.dataChunks : Array.<Uint8Array>

Image Data pieces

Kind: instance property of ImagePNG

imagePNG.header : Array | Uint8Array

PNG Signature from the data

Kind: instance property of ImagePNG

imagePNG.setBitDepth(bitDepth)

Sets the bitDepth on the ImagePNG instance.

Kind: instance method of ImagePNG

Param	Type	Description
bitDepth	number	The bitDepth to set, one of: 1, 2, 4, 8, 16

imagePNG.setColorType(colorType)

Sets the colorType on the ImagePNG instance. Both color and alpha properties are inferred from the colorType.

Color Type	Allowed Bit Depths	Interpretation
0	1, 2, 4, 8, 16	Each pixel is a grayscale sample.
2	8, 16	Each pixel is an R, G, B triple.
3	1, 2, 4, 8	Each pixel is a palette index; a PLTE chunk must appear.
4	8, 16	Each pixel is a grayscale sample, followed by an alpha sample.
6	8, 16	Each pixel is an R, G, B triple, followed by an alpha sample.

Kind: instance method of ImagePNG
Throws:

• Error Invalid Color Type, anything other than 0, 2, 3, 4, 6

Param	Type	Description
colorType	number	The colorType to set, one of: 0, 2, 3, 4, 6

imagePNG.setCompressionMethod(compressionMethod)

Sets the compressionMethod on the ImagePNG instance. The compressionMethod should always be 0.

Kind: instance method of ImagePNG
Throws:

• Error Unsupported Compression Method, anything other than 0

Param	Type	Description
compressionMethod	number	The compressionMethod to set, always 0

imagePNG.setFilterMethod(filterMethod)

Sets the filterMethod on the ImagePNG instance. The filterMethod should always be 0.

Kind: instance method of ImagePNG
Throws:

• Error Unsupported Filter Method, anything other than 0

Param	Type	Description
filterMethod	number	The filterMethod to set, always 0

imagePNG.setInterlaceMethod(interlaceMethod)

Sets the interlaceMethod on the ImagePNG instance. The interlaceMethod should always be 0 or 1.

Kind: instance method of ImagePNG
Throws:

• Error Unsupported Interlace Method, anything other than 0 or 1

Param	Type	Description
interlaceMethod	number	The filterMethod to set, always 0 or 1

imagePNG.setPalette(palette)

Sets the palette on the ImagePNG instance.

Kind: instance method of ImagePNG
Throws:

• Error No colors in the palette
• Error Too many colors for the current bit depth

Param	Type	Description
palette	Array.<number> | Uint8Array	The palette to set

imagePNG.getPixel(x, y) ⇒ Array

Get the pixel color at a specified x, y location.

Kind: instance method of ImagePNG
Returns: Array - the color as [red, green, blue, alpha]
Throws:

• Error x is out of bound for the image
• Error y is out of bound for the image
• Error Unknown color types

Param	Type	Description
x	number	The hoizontal offset to read.
y	number	The vertical offset to read.

imagePNG.parse()

Parse the PNG file, decoding the supported chunks.

Kind: instance method of ImagePNG

imagePNG.decodeHeader()

Decodes and validates PNG Header. Signature (Decimal): [137, 80, 78, 71, 13, 10, 26, 10] Signature (Hexadecimal): [89, 50, 4E, 47, 0D, 0A, 1A, 0A] Signature (ASCII): [\211, P, N, G, \r, \n, \032, \n]

Kind: instance method of ImagePNG
Throws:

• Error Missing or invalid PNG header

See: PNG Signature

imagePNG.decodeChunk() ⇒ string

Decodes the chunk type, and attempts to parse that chunk if supported. Supported Chunk Types: IHDR, PLTE, IDAT, IEND, tRNS, pHYs

Chunk Structure: Length: 4 bytes Type: 4 bytes (IHDR, PLTE, IDAT, IEND, etc.) Chunk: {length} bytes CRC: 4 bytes

Kind: instance method of ImagePNG
Returns: string - Chunk Type
Throws:

• Error Invalid Chunk Length when less than 0

See: Chunk Layout

imagePNG.decodeIHDR(chunk)

Decode the IHDR (Image header) chunk. Should be the first chunk in the data stream.

Width: 4 bytes Height: 4 bytes Bit Depth: 1 byte Colour Type: 1 byte Compression Method: 1 byte Filter Method: 1 byte Interlace Method: 1 byte

Kind: instance method of ImagePNG
See

• Image Header
• Image Header

Param	Type	Description
chunk	Uint8Array	Data Blob

imagePNG.decodePLTE(chunk)

Decode the PLTE (Palette) chunk. The PLTE chunk contains from 1 to 256 palette entries, each a three-byte series of the form. The number of entries is determined from the chunk length. A chunk length not divisible by 3 is an error.

Kind: instance method of ImagePNG
See: Palette

Param	Type	Description
chunk	Uint8Array	Data Blob

imagePNG.decodeIDAT(chunk)

Decode the IDAT (Image Data) chunk. The IDAT chunk contains the actual image data which is the output stream of the compression algorithm.

Kind: instance method of ImagePNG
See: Image Data

Param	Type	Description
chunk	Uint8Array	Data Blob

imagePNG.decodeTRNS(chunk)

Decode the tRNS (Transparency) chunk. The tRNS chunk specifies that the image uses simple transparency: either alpha values associated with palette entries (for indexed-color images) or a single transparent color (for grayscale and truecolor images). Although simple transparency is not as elegant as the full alpha channel, it requires less storage space and is sufficient for many common cases.

Kind: instance method of ImagePNG
See: Transparency

Param	Type	Description
chunk	Uint8Array	Data Blob

imagePNG.decodePHYS(chunk)

Decode the pHYs (Pixel Dimensions) chunk. The pHYs chunk specifies the intended pixel size or aspect ratio for display of the image. When the unit specifier is 0, the pHYs chunk defines pixel aspect ratio only; the actual size of the pixels remains unspecified. If the pHYs chunk is not present, pixels are assumed to be square, and the physical size of each pixel is unspecified.

Structure: Pixels per unit, X axis: 4 bytes (unsigned integer) Pixels per unit, Y axis: 4 bytes (unsigned integer) Unit specifier: 1 byte 0: unit is unknown 1: unit is the meter

Kind: instance method of ImagePNG
See: Pixel Dimensions

Param	Type	Description
chunk	Uint8Array	Data Blob

imagePNG.decodeIEND(_chunk)

Decode the IEND (Image trailer) chunk. The IEND chunk marks the end of the PNG DataBuffer. The chunk's data field is empty.

Kind: instance method of ImagePNG
See: Image Trailer

Param	Type	Description
_chunk	Uint8Array	Unused.

imagePNG.decodePixels()

Uncompress IDAT chunks.

Kind: instance method of ImagePNG
Throws:

• Error No IDAT chunks to decode
• Error Deinterlacing Error
• Error Inflating Error
• Error Adam7 interlaced format is unsupported

imagePNG.interlaceNone(data)

Deinterlace with no interlacing.

Kind: instance method of ImagePNG
See: PNG Filters

Param	Type	Description
data	Buffer	Data to deinterlace.

imagePNG.unFilterNone(scanline, bpp, offset, length)

No filtering, direct copy.

Kind: instance method of ImagePNG

Param	Type	Description
scanline	Array | Uint8Array	Scanline to search for pixels in.
bpp	number	Bytes Per Pixel
offset	number	Offset
length	number	Length

imagePNG.unFilterSub(scanline, bpp, offset, length)

The Sub() filter transmits the difference between each byte and the value of the corresponding byte of the prior pixel. Sub(x) = Raw(x) + Raw(x - bpp)

Kind: instance method of ImagePNG

Param	Type	Description
scanline	Array | Uint8Array	Scanline to search for pixels in.
bpp	number	Bytes Per Pixel
offset	number	Offset
length	number	Length

ImagePNG.fromFile(data) ⇒ ImagePNG

Creates a new ImagePNG from file data.

Kind: static method of ImagePNG
Returns: ImagePNG - the new ImagePNG instance for the provided file data

Param	Type	Description
data	Array | ArrayBuffer | Buffer | DataBuffer | Int8Array | Int16Array | Int32Array | number | string | Uint8Array | Uint16Array | Uint32Array	The data of the image to process.

ImagePNG.fromBuffer(buffer) ⇒ ImagePNG

Creates a new ImagePNG from a DataBuffer.

Kind: static method of ImagePNG
Returns: ImagePNG - the new ImagePNG instance for the provided DataBuffer

Param	Type	Description
buffer	DataBuffer	The DataBuffer of the image to process.

debug() : function

Kind: global function

---

Tests

To run the test suite, first install the dependencies, then run npm test:

1npm install
2npm test
3DEBUG=Uttori* npm test

Contributors

• Matthew Callis

License

• MIT