class

CrImage::PNG::Reader

Inherits IO / Reference / Object

PNG image format decoder

Implements PNG (Portable Network Graphics) decoding according to the PNG specification. Supports all color types, bit depths, interlacing, and transparency modes.

Class methods

read(path : String) : CrImage::Image

read and decode the entire image

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read(io : IO) : CrImage::Image
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read_config(path : String) : CrImage::Config

read and decode the configurations like color model, dimensions and does not decode entire image. This returns CrImage::Config instead.

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read_config(io : IO) : CrImage::Config
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Instance methods

depth
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height
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image
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read(slice : Bytes)

Reads at most slice.size bytes from this IO into slice. Returns the number of bytes read, which is 0 if and only if there is no more data to read (so checking for 0 is the way to detect end of file).

io = IO::Memory.new "hello"
slice = Bytes.new(4)
io.read(slice) # => 4
slice          # => Bytes[104, 101, 108, 108]
io.read(slice) # => 1
slice          # => Bytes[111, 101, 108, 108]
io.read(slice) # => 0
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read_bytes(n)

Reads an instance of the given type from this IO using the specified format.

This ends up invoking type.from_io(self, format), so any type defining a from_io(io : IO, format : IO::ByteFormat = IO::ByteFormat::SystemEndian) method can be read in this way.

See Int.from_io and Float.from_io.

io = IO::Memory.new
io.puts "\u{4}\u{3}\u{2}\u{1}"
io.rewind
io.read_bytes(Int32, IO::ByteFormat::LittleEndian) # => 0x01020304
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width
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write(slice : Bytes) : Nil

Writes the contents of slice into this IO.

io = IO::Memory.new
slice = Bytes.new(4) { |i| ('a'.ord + i).to_u8 }
io.write(slice)
io.to_s # => "abcd"
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