Global

Members

(constant) ChunkType :ChunkType

An enum for standard PNG chunk type codes (4-byte Uint32 decimal), including critical and ancillary chunks.
Type:
Properties:
Name Type Description
IHDR number
PLTE number
IDAT number
IEND number
(...) number see source for full list
Source:

(constant) ColorType :ColorType

An enum for standard PNG color types, such as RGB or RGBA.
Type:
Properties:
Name Type Description
GRAYSCALE number (1)
RGB number (2)
INDEXED number (3)
GRAYSCALE_ALPHA number (4)
RGBA number (6)
Source:

(constant) FilterMethod :FilterMethod

An enum for standard PNG scanline filter methods.
Type:
Properties:
Name Type Description
None number No filter (0x00)
Sub number Compute from left (0x01)
Up number Compute from above scanline (0x02)
Average number Compute from average of up and left (0x03)
Paeth number Compute the PNG 'paeth' predictor from up & left (0x04)
Source:

(constant) Intent :Intent

An enum for Intent when specifying sRGB chunk.
Type:
Properties:
Name Type Description
Perceptual number (0x00)
Relative number relative colorimetric (0x01)
Saturation number (0x02)
Absolute number absolute colorimetric (0x03)
Source:

Methods

chunkNameToType(name) → {number}

Converts a 4-character ASCII string into a 4-byte (32-bit) integer representing a chunk type.
Parameters:
Name Type Description
name string the name of the chunk
Source:
Returns:
a 32-bit integer representing this chunk type
Type
number

chunkTypeToName(type) → {string}

Converts an arbitrary 4-byte chunk type into a readable ASCII string.
Parameters:
Name Type Description
type number the chunk type
Source:
Returns:
a name representing this type
Type
string

colorTypeToString(colorType) → {string}

Converts a ColorType enum to a human readable string, for example ColorType.RGBA (= 6) becomes "RGBA". Although these numerical constants are defined in the PNG spec, the exact string for each is not.
Parameters:
Name Type Description
colorType ColorType the type to convert
Source:
Returns:
a readable string
Type
string

crc32(buf, copt) → {number}

Calculate the CRC32 checksum of an array-like buffer.
Parameters:
Name Type Attributes Default Description
buf ArrayLike the array-like buffer to calculate the CRC32 of
c number <optional>
 -1 the initial CRC32 value
Source:
Returns:
the CRC32 checksum
Type
number

decode_IHDR(data) → {IHDRData}

Decodes the IHDR chunk data, which gives information about the PNG image. The chunk data does not include the length or chunk type fields, nor the CRC32 checksum.
Parameters:
Name Type Description
data ArrayBufferView a typed array input, typically Uint8Array
Source:
Returns:
the decoded IHDR data as a plain JS object
Type
IHDRData

decode_iCCP(data) → {iCCPData}

Decodes iCCP (color profile) chunk data and returns an object.
Parameters:
Name Type Description
data ArrayBufferView the chunk data, typically Uint8Array
Source:
Returns:
the iCCP chunk metadata
Type
iCCPData

decode_iTXt(data) → {iTXtData}

Decodes iTXt (international text) chunk data and returns an object.
Parameters:
Name Type Description
data ArrayBufferView the chunk data, typically Uint8Array
Source:
Returns:
the iTXt chunk metadata
Type
iTXtData

decode_pHYs(data) → {pHYsData}

Decodes pHYs (physical pixel dimensions) chunk data and returns an object.
Parameters:
Name Type Description
data ArrayBufferView the chunk data, typically Uint8Array
Source:
Returns:
the pHYs chunk metadata
Type
pHYsData

decode_pHYs_PPI(data) → {number}

Decodes the pHYs chunk data and returns the pixels per inch value. This expects the data's x and y to be equal and the unit to be meters. Note that since the value is rounded during encoding, the resulting PPI might not be exactly the same as the original.
Parameters:
Name Type Description
data ArrayBufferView the chunk data, typically Uint8Array
Source:
Returns:
the pixels per inch value, or null if the data is invalid
Type
number

encode(options, deflate, deflateOptionsopt)

Encodes a PNG buffer from the given image and options, using the specified `deflate` algorithm and optional compression options. The deflate function should have the signature `(buf, [deflateOptions]) => Uint8Array`.
Parameters:
Name Type Attributes Description
options EncodeOptions the encoding options
deflate function the sync deflate function to use
deflateOptions Object <optional>
 optional deflate options passed to the deflate() function
Source:

encodeChunk(chunk) → {Uint8Array}

Encodes a single PNG chunk into a Uint8Array buffer, by writing the chunk length, type, data, and CRC value.
Parameters:
Name Type Description
chunk Chunk the chunk to encode
Source:
Returns:
the encoded chunk buffer
Type
Uint8Array

encodeHeader() → {Uint8Array}

Encodes just the raw PNG header into a Uint8Array buffer.
Source:
Returns:
the PNG header
Type
Uint8Array

encode_IDAT_raw(data, opts) → {Uint8Array}

Encodes an image scanline (or sequence of scanlines) in the form of IDAT chunk data (a Uint8Array). This will use the specified `filter` parameter, or default to Paeth, which is a good general-purpose filter. You can set the filter to `FilterMethod.None`, which will be much more efficient but may compress poorly. Note that if you are using many chunks of IDAT data, such as for parallel encoding, you'll want to set the `firstFilter` to either `FilterMethod.None` or `FilterMethod.Sub` (the others require the previous scanline to be available).
Parameters:
Name Type Description
data ArrayBufferView the raw image pixel data
opts IDATParameters the IDAT parameters
Source:
Returns:
the encoded IDAT data
Type
Uint8Array

encode_IHDR(data) → {Uint8Array}

Encodes the IHDR metadata as a Uint8Array buffer. Depth defaults to 8, colorType defaults to ColorType.RGBA, and interlace defaults to 0.
Parameters:
Name Type Description
data IHDRData the IHDR metadata
Source:
Returns:
the encoded IHDR data
Type
Uint8Array

encode_iCCP(opts) → {Uint8Array}

Encodes iCCP (color profile) metadata as a Uint8Array buffer. The data is expected to already be compressed by DEFLATE, and the `compression` flag is ignored and set to 0 as it is the only valid value defined by the PNG spec.
Parameters:
Name Type Description
opts iCCPData the iCCP metadata
Source:
Returns:
the encoded iCCP data
Type
Uint8Array

encode_iTXt(opts) → {Uint8Array}

Encodes iTXt (international text) metadata as a Uint8Array buffer.
Parameters:
Name Type Description
opts iTXtData the iTXt metadata
Source:
Returns:
the encoded iTXt data
Type
Uint8Array

encode_pHYs(opts) → {Uint8Array}

Encodes pHYs (physical pixel dimensions) metadata as a Uint8Array buffer.
Parameters:
Name Type Description
opts pHYsData the pHYs metadata
Source:
Returns:
the encoded pHYs data
Type
Uint8Array

encode_pHYs_PPI(pixelsPerInch) → {Uint8Array}

Encodes a pHYs chunk with a pixels per inch value, this is mostly a convenience function.
Parameters:
Name Type Description
pixelsPerInch number the number of pixels per inch, such as 72 (web) or 300 (print) DPI
Source:
Returns:
the encoded pHYs data
Type
Uint8Array

encode_sRGB(intent) → {Uint8Array}

Encodes an sRGB chunk with an intent value.
Parameters:
Name Type Description
intent Intent the rendering intent
Source:
Returns:
the encoded sRGB data
Type
Uint8Array

encode_standardChromatics() → {Uint8Array}

Encodes a standard chromatics chunk, useful as a default.
Source:
Returns:
the encoded chromatics data
Type
Uint8Array

encode_standardGamma() → {Uint8Array}

Encodes a standard sRGB gamma chunk, useful as a default.
Source:
Returns:
the encoded sRGB gamma data
Type
Uint8Array

flattenBuffers(chunks)

Concatenates a given array of array-like data (array buffers, typed arrays) into a single Uint8Array.
Parameters:
Name Type Description
chunks Array.<ArrayLike>
Source:
Returns:
Uint8Array concatenated data

readChunks(buf, optsopt) → {Array.<Chunk>}

Parses a PNG buffer and returns an array of chunks, each containing a type code and its data. The individual chunks are not decoded, but left as raw Uint8Array data. If `copy` option is `false`, the chunk data is a view into the original ArrayBufferView (no copy involved), which is more memory efficient for large files.
Parameters:
Name Type Attributes Default Description
buf ArrayBufferView
opts PNGReaderOptions <optional>
 {} optional parameters for reading PNG chunks
Source:
Returns:
an array of chunks
Type
Array.<Chunk>

readIHDR(buf, optsopt) → {IHDRData}

Reads a PNG buffer up to the end of the IHDR chunk and returns this metadata, giving its width, height, bit depth, and color type.
Parameters:
Name Type Attributes Default Description
buf ArrayBufferView the PNG buffer to read
opts PNGReaderOptions <optional>
 {} optional parameters for reading
Source:
Returns:
Type
IHDRData

reader(buf, optsopt) → {Array.<Chunk>}

A low-level interface for stream reading a PNG file. With the speicifed buffer, this function reads each chunk and calls the `read(type, data)` function, which is expected to do something with the chunk data. If the `read()` function returns `false`, the stream will stop reading the rest of the PNG file and safely end early, otherwise it will expect to end on an IEND type chunk to form a valid PNG file.
Parameters:
Name Type Attributes Default Description
buf ArrayBufferView
opts PNGReaderOptions <optional>
 {} optional parameters for reading PNG chunks
Source:
Returns:
an array of chunks
Type
Array.<Chunk>

writeChunks(chunks) → {Uint8Array}

Writes and formats an array of PNG chunks into a complete PNG buffer, including the PNG header.
Parameters:
Name Type Description
chunks Array.<Chunk> the array of chunks to encode
Source:
Returns:
the encoded PNG buffer
Type
Uint8Array

Type Definitions

Chunk

Properties:
Name Type Description
type number the chunk type code as a 4-byte Uint32 value (ASCII string)
data Uint8Array the chunk data (not including chunk length, type, or CRC checksum)
Source:

EncodeOptions

Type:
  • Object
Properties:
Name Type Attributes Default Description
data Uint8Array the raw pixel data to encode
width number the width of the image
height number the height of the image
colorType ColorType <optional>
 ColorType.RGBA the color type of the pixel data
depth number <optional>
 8 the bit depth of the image
filterMethod number <optional>
 FilterMethod.Paeth the filter method to use
firstFilter number <optional>
 filter the first scanline filter method to use
ancillary Array.<Chunk> <optional>
 [] additional chunks to include in the PNG
Source:

IDATParameters

Properties:
Name Type Attributes Default Description
width number the width of the image in pixels
height number the height of the image in pixels
depth number <optional>
 8 the bit depth of the image (default 8)
colorType ColorType <optional>
 ColorType.RGBA the color type of the image (default RGBA)
filter FilterMethod <optional>
 FilterMethod.Paeth the filter method to use (default Paeth)
firstFilter FilterMethod <optional>
 filter the filter method to use for the *first* scanline (defaults to provided `filter`)
Source:

IHDRData

Type:
  • Object
Properties:
Name Type Description
width number the width of the image in pixels
height number the height of the image in pixels
depth number the bit depth of the image
colorType ColorType the color type of the image
compression number the compression method of the image (always 0 in well-formed PNGs)
filter number the filter specification (always 0 in well-formed PNGs, note this is not the same as FilterMethod)
interlace number the interlace method of the image (0 for no interlace, 1 for Adam7 interlace)
Source:

PNGReaderOptions

Type:
  • Object
Properties:
Name Type Attributes Default Description
checkCRC boolean <optional>
 false whether to check and verify CRC values of each chunk (slower but can detect errors and corruption earlier during parsing)
copy boolean <optional>
 true whether to return a sliced copy of each chunk data instead of a shallow subarray view into the input buffer
Source:

iCCPData

Type:
  • Object
Properties:
Name Type Description
name string the name of the color profile
compression number the compression method used (always 0 for well-formed PNG, implying DEFLATE)
data Uint8Array the compressed color profile data
Source:

iTXtData

Type:
  • Object
Properties:
Name Type Description
keyword string the keyword for this text chunk
compressionFlag number the compression flag (0 for no compression, 1 for compression)
compressionMethod number the compression method (0 for zlib)
languageTag string the language tag
translatedKeyword string the translated keyword
text string the text data
Source:

pHYsData

Type:
  • Object
Properties:
Name Type Description
x number the number of pixels per unit in the x direction
y number the number of pixels per unit in the y direction
unit number the unit specifier (0 for unknown, 1 for meter)
Source: