Codec.Picture.Gif

Module implementing GIF decoding.

Reading

decodeGif :: ByteString -> Either String DynamicImage

Transform a raw gif image to an image, without modifying the pixels. This function can output the following images:

• ImageRGB8
• ImageRGBA8

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

Transform a raw gif image to an image, without modifying the pixels. This function can output the following images:

• ImageRGB8
• ImageRGBA8

Metadatas include Width & Height information.

decodeGifWithPaletteAndMetadata :: ByteString -> Either String (PalettedImage, Metadatas)

Return the gif image with metadata and palette. The palette is only returned for the first image of an animation and has no transparency.

decodeGifImages :: ByteString -> Either String [DynamicImage]

Transform a raw gif to a list of images, representing all the images of an animation.

getDelaysGifImages :: ByteString -> Either String [GifDelay]

Extract a list of frame delays from a raw gif.

Writing

type GifDelay = Int

Delay to wait before showing the next Gif image. The delay is expressed in 100th of seconds.

data GifDisposalMethod

Constructors

DisposalAny

DisposalDoNot

DisposalRestoreBackground

DisposalRestorePrevious

DisposalUnknown Word8

data GifEncode

GIF image definition for encoding

Constructors

GifEncode

Fields

• geWidth :: Int

  Screen width

• geHeight :: Int

  Screen height

• gePalette :: Maybe Palette

  Global palette, optional

• geBackground :: Maybe Int

  Background color index, optional. If given, a global palette is also required

• geLooping :: GifLooping

  Looping behaviour

• geFrames :: [GifFrame]

  Image frames

data GifFrame

An individual image frame in a GIF image

Constructors

GifFrame

Fields

• gfXOffset :: Int

  Image X offset in GIF canvas

• gfYOffset :: Int

  Image Y offset in GIF canvas

• gfPalette :: Maybe Palette

  Image local palette, optional if a global palette is given

• gfTransparent :: Maybe Int

  Transparent color index, optional

• gfDelay :: GifDelay

  Frame transition delay, in 1/100ths of a second

• gfDisposal :: GifDisposalMethod

  Frame disposal method

• gfPixels :: Image Pixel8

  Image pixels

data GifLooping

Help to control the behaviour of GIF animation looping.

Constructors

LoopingNever

The animation will stop once the end is reached

LoopingForever

The animation will restart once the end is reached

LoopingRepeat Word16

The animation will repeat n times before stoping

encodeGifImage :: Image Pixel8 -> ByteString

Encode a greyscale image to a bytestring.

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

Encode an image with a given palette. Can return errors if the palette is ill-formed.

• A palette must have between 1 and 256 colors

encodeGifImages :: GifLooping -> [(Palette, GifDelay, Image Pixel8)] -> Either String ByteString

Encode a gif animation to a bytestring.

• Every image must have the same size
• Every palette must have between one and 256 colors.

encodeComplexGifImage :: GifEncode -> Either String ByteString

Encode a complex gif to a bytestring.

• There must be at least one image.
• The screen and every frame dimensions must be between 1 and 65535.
• Every frame image must fit within the screen bounds.
• Every palette must have between one and 256 colors.
• There must be a global palette or every image must have a local palette.
• The background color index must be present in the global palette.
• Every frame's transparent color index, if set, must be present in the palette used by that frame.
• Every color index used in an image must be present in the palette used by that frame.

writeGifImage :: FilePath -> Image Pixel8 -> IO ()

Write a greyscale in a gif file on the disk.

writeGifImageWithPalette :: FilePath -> Image Pixel8 -> Palette -> Either String (IO ())

Write a gif image with a palette to a file.

• A palette must have between 1 and 256 colors

writeGifImages :: FilePath -> GifLooping -> [(Palette, GifDelay, Image Pixel8)] -> Either String (IO ())

Write a list of images as a gif animation in a file.

• Every image must have the same size
• Every palette must have between one and 256 colors.

writeComplexGifImage :: FilePath -> GifEncode -> Either String (IO ())

greyPalette :: Palette

Default palette to produce greyscale images.