Codec.Picture.Png

Module used for loading & writing 'Portable Network Graphics' (PNG) files.

A high level API is provided. It loads and saves images for you while hiding all the details about PNG chunks.

Basic functions for PNG handling are decodePng, encodePng and encodePalettedPng. Convenience functions are provided for direct file handling and using DynamicImages.

The loader has been validated against the pngsuite (http:/www.libpng.orgpubpngpngsuite.html)

High level functions

class PngSavable a where

Encode an image into a png if possible.

Minimal complete definition

encodePngWithMetadata

Methods

encodePng :: Image a -> ByteString

Transform an image into a png encoded bytestring, ready to be written as a file.

encodePngWithMetadata :: Metadatas -> Image a -> ByteString

Encode a png using some metadatas. The following metadata keys will be stored in a tEXt field :

• Title
• Description
• Author
• Copyright
• Software
• Comment
• Disclaimer
• Source
• Warning
• Unknown using the key present in the constructor.

the followings metadata will bes tored in the gAMA chunk.

• Gamma

The followings metadata will be stored in a pHYs chunk

• DpiX
• DpiY

Instances

PngSavable PixelRGBA16

PngSavable PixelRGBA8

PngSavable PixelRGB16

PngSavable PixelRGB8

PngSavable PixelYA16

PngSavable PixelYA8

PngSavable Pixel16

PngSavable Pixel8

decodePng :: ByteString -> Either String DynamicImage

Transform a raw png image to an image, without modifying the underlying pixel type. If the image is greyscale and < 8 bits, a transformation to RGBA8 is performed. This should change in the future. The resulting image let you manage the pixel types.

This function can output the following pixel types:

• PixelY8

  • PixelY16
  • PixelYA8
  • PixelYA16
  • PixelRGB8
  • PixelRGB16
  • PixelRGBA8
  • PixelRGBA16

decodePngWithMetadata :: ByteString -> Either String (DynamicImage, Metadatas)

Same as decodePng but also extract meta datas present in the files.

writePng :: PngSavable pixel => FilePath -> Image pixel -> IO ()

Helper function to directly write an image as a png on disk.

encodeDynamicPng :: DynamicImage -> Either String ByteString

Encode a dynamic image in bmp if possible, supported pixel type are :

• Y8
• Y16
• YA8
• YA16
• RGB8
• RGB16
• RGBA8
• RGBA16

encodePalettedPng :: Palette -> Image Pixel8 -> Either String ByteString

Encode a paletted image as a color indexed 8-bit PNG. the palette must have between 1 and 256 values in it.

encodePalettedPngWithMetadata :: Metadatas -> Palette -> Image Pixel8 -> Either String ByteString

Equivalent to encodePalettedPng but allow writing of metadatas.

writeDynamicPng :: FilePath -> DynamicImage -> IO (Either String Bool)

Write a dynamic image in a .png image file if possible. The same restriction as encodeDynamicPng apply.