PNGReader

Classes

• PNGReader

Functions

• inflate(encoded_chunk) ⇒ ArrayBuffer

• readUInt32(buffer, offset) ⇒ number

• readUInt8(buffer, offset) ⇒ number

PNGReader

Kind: global class

• PNGReader
  • new exports.PNGReader(bytes)
  • .i : number
  • .bytes : Uint8Array
  • .png : PNG
  • .dataChunks : Array.<Uint8Array>
  • .buffer : BinaryBuffer
  • .crc_enabled : boolean
  • .header : Uint8Array
  • .readBytes(length) ⇒ Uint8Array
  • .decodeHeader()
  • .decodeChunk() ⇒ string
    • ~chunk : Uint8Array
  • .decodesRGB(chunk)
  • .decodetIME(chunk)
  • .decodeiTXt(chunk)
  • .decodezTXt(chunk)
  • .decodetEXt(chunk)
  • .decodeiEXt(chunk)
  • .decodeIHDR()
  • .decodePLTE(chunk)
  • .decodeIDAT()
  • .decodeTRNS(chunk)
  • .decodeIEND()
  • .decodePixels()
  • .interlaceNone(data)
  • .interlaceAdam7(data)
  • .unFilter(filter_type, data, scanline_address, output, bytes_per_pixel, output_offset, output_offset_previous, length)
  • .unFilterNone(data, scanline_address, output, bytes_per_pixel, output_offset, output_offset_previous, length)
  • .unFilterSub(scanline, scanline_offset, pixels, bpp, offset, output_offset_previous, length)
  • .unFilterUp(scanline, scanline_offset, pixels, bpp, offset, output_offset_previous, length)
  • .unFilterAverage(scanline, scanline_offset, pixels, bpp, offset, output_offset_previous, length)
  • .unFilterPaeth(scanline, scanline_offset, pixels, bpp, offset, output_offset_previous, length)
  • .parse() ⇒ PNG

new exports.PNGReader(bytes)

Param	Type
bytes	ArrayBuffer

pngReader.i : number

current pointer

Kind: instance property of PNGReader

pngReader.bytes : Uint8Array

bytes buffer

Kind: instance property of PNGReader

pngReader.png : PNG

Output object

Kind: instance property of PNGReader

pngReader.dataChunks : Array.<Uint8Array>

Kind: instance property of PNGReader

pngReader.buffer : BinaryBuffer

Kind: instance property of PNGReader

pngReader.crc_enabled : boolean

Whether CRC should be performed or not

Kind: instance property of PNGReader

pngReader.header : Uint8Array

Kind: instance property of PNGReader

pngReader.readBytes(length) ⇒ Uint8Array

Kind: instance method of PNGReader

Param	Type
length	number

pngReader.decodeHeader()

http://www.w3.org/TR/2003/REC-PNG-20031110/#5PNG-file-signature

Kind: instance method of PNGReader

pngReader.decodeChunk() ⇒ string

http://www.w3.org/TR/2003/REC-PNG-20031110/#5Chunk-layout

length = 4 bytes type = 4 bytes (IHDR, PLTE, IDAT, IEND or others) chunk = length bytes crc = 4 bytes

Kind: instance method of PNGReader
Returns: string - chunk type

decodeChunk~chunk : Uint8Array

Kind: inner constant of decodeChunk

pngReader.decodesRGB(chunk)

https://www.w3.org/TR/2003/REC-PNG-20031110/#11sRGB

Kind: instance method of PNGReader

Param	Type
chunk	Uint8Array

pngReader.decodetIME(chunk)

https://www.w3.org/TR/2003/REC-PNG-20031110/#11tIME

Kind: instance method of PNGReader

Param	Type
chunk	Uint8Array

pngReader.decodeiTXt(chunk)

International textual data

Kind: instance method of PNGReader
See: https://www.w3.org/TR/2003/REC-PNG-20031110/

Param	Type
chunk	Uint8Array

pngReader.decodezTXt(chunk)

Compressed textual data

Kind: instance method of PNGReader
See: https://www.w3.org/TR/2003/REC-PNG-20031110/#11zTXt

Param	Type
chunk	Uint8Array

pngReader.decodetEXt(chunk)

https://www.w3.org/TR/PNG/#11tEXt

Kind: instance method of PNGReader

Param	Type
chunk	Uint8Array

pngReader.decodeiEXt(chunk)

NOTE: untested https://www.w3.org/TR/PNG/#11iEXt

Kind: instance method of PNGReader

Param	Type
chunk	Uint8Array

pngReader.decodeIHDR()

http://www.w3.org/TR/2003/REC-PNG-20031110/#11IHDR http://www.libpng.org/pub/png/spec/1.2/png-1.2-pdg.html#C.IHDR

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 PNGReader

pngReader.decodePLTE(chunk)

http://www.w3.org/TR/PNG/#11PLTE

Kind: instance method of PNGReader

Param	Type
chunk	Uint8Array

pngReader.decodeIDAT()

http://www.w3.org/TR/2003/REC-PNG-20031110/#11IDAT

Kind: instance method of PNGReader

pngReader.decodeTRNS(chunk)

https://www.w3.org/TR/PNG/#11tRNS

Kind: instance method of PNGReader

Param	Type
chunk	Uint8Array

pngReader.decodeIEND()

http://www.w3.org/TR/2003/REC-PNG-20031110/#11IEND

Kind: instance method of PNGReader

pngReader.decodePixels()

Uncompress IDAT chunks

Kind: instance method of PNGReader

pngReader.interlaceNone(data)

Kind: instance method of PNGReader

Param	Type
data	Uint8Array

pngReader.interlaceAdam7(data)

De-interlace image according to Adam 7 scheme

Kind: instance method of PNGReader

Param	Type
data	Uint8Array

pngReader.unFilter(filter_type, data, scanline_address, output, bytes_per_pixel, output_offset, output_offset_previous, length)

Kind: instance method of PNGReader
See: https://www.w3.org/TR/PNG-Filters.html

Param	Type	Description
filter_type	number
data	Uint8Array
scanline_address	number
output	Uint8Array
bytes_per_pixel	number
output_offset	number
output_offset_previous	number	where does result of previous scanline begin in the output? Needed for various filters such as Up
length	number

pngReader.unFilterNone(data, scanline_address, output, bytes_per_pixel, output_offset, output_offset_previous, length)

With the None filter, the scanline is transmitted unmodified; it is only necessary to insert a filter type byte before the data.

Kind: instance method of PNGReader
See: https://www.w3.org/TR/PNG-Filters.html

Param	Type
data	Uint8Array
scanline_address	number
output	Uint8Array
bytes_per_pixel	number
output_offset	number
output_offset_previous	number
length	number

pngReader.unFilterSub(scanline, scanline_offset, pixels, bpp, offset, output_offset_previous, 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 PNGReader
See: https://www.w3.org/TR/PNG-Filters.html

Param	Type	Description
scanline	Uint8Array	raw data
scanline_offset	number
pixels	Uint8Array	processed output
bpp	number	bytes-per-pixel
offset	number
output_offset_previous	number
length	number

pngReader.unFilterUp(scanline, scanline_offset, pixels, bpp, offset, output_offset_previous, length)

The Up filter is just like the Sub() filter except that the pixel immediately above the current pixel, rather than just to its left, is used as the predictor. Up(x) = Raw(x) + Prior(x)

Kind: instance method of PNGReader
See: https://www.w3.org/TR/PNG-Filters.html

Param	Type	Description
scanline	Uint8Array	raw data
scanline_offset	number
pixels	Uint8Array	processed output
bpp	number	bytes-per-pixel
offset	number
output_offset_previous	number
length	number

pngReader.unFilterAverage(scanline, scanline_offset, pixels, bpp, offset, output_offset_previous, length)

The Average filter uses the average of the two neighboring pixels (left and above) to predict the value of a pixel.

Average(x) = Raw(x) + floor((Raw(x-bpp)+Prior(x))/2)

Kind: instance method of PNGReader
See: https://www.w3.org/TR/PNG-Filters.html

Param	Type	Description
scanline	Uint8Array	raw data
scanline_offset	number
pixels	Uint8Array	processed output
bpp	number	bytes-per-pixel
offset	number
output_offset_previous	number
length	number

pngReader.unFilterPaeth(scanline, scanline_offset, pixels, bpp, offset, output_offset_previous, length)

The Paeth filter computes a simple linear function of the three neighboring pixels (left, above, upper left), then chooses as predictor the neighboring pixel closest to the computed value.

This technique is due to Alan W. Paeth.

Kind: instance method of PNGReader
See: https://www.w3.org/TR/PNG-Filters.html

Param	Type	Description
scanline	Uint8Array	raw data
scanline_offset	number
pixels	Uint8Array	processed output
bpp	number	bytes-per-pixel
offset	number
output_offset_previous	number
length	number

pngReader.parse() ⇒ PNG

Parse the PNG file

Kind: instance method of PNGReader

inflate(encoded_chunk) ⇒ ArrayBuffer

Kind: global function

Param	Type
encoded_chunk	Uint8Array

readUInt32(buffer, offset) ⇒ number

Kind: global function

Param	Type
buffer	Uint8Array
offset	number

readUInt8(buffer, offset) ⇒ number

Kind: global function

Param	Type
buffer	Uint8Array
offset	number