Codec.Picture

Main module exporting import/export functions into various image formats.

To use the library without thinking about it, look after decodeImage and readImage.

Generally, the read* functions read the images from a file and try to decode it, and the decode* functions try to decode a bytestring.

For an easy image writing use the write* functions and writeDynamic* functions.

Generic functions

readImage :: FilePath -> IO (Either String DynamicImage)

Load an image file without even thinking about it, it does everything as decodeImage

decodeImage :: ByteString -> Either String DynamicImage

If you want to decode an image in a bytestring without even thinking in term of format or whatever, this is the function to use. It will try to decode in each known format and if one decoding succeed will return the decoded image in it's own colorspace

Specific image format functions

Bitmap handling

class BmpEncodable pixel

All the instance of this class can be written as a bitmap file using this library.

Instances

BmpEncodable PixelRGBA8

BmpEncodable PixelRGB8

BmpEncodable Pixel8

writeBitmap :: BmpEncodable pixel => FilePath -> Image pixel -> IO ()

Write an image in a file use the bitmap format.

encodeBitmap :: forall pixel. BmpEncodable pixel => Image pixel -> ByteString

Encode an image into a bytestring in .bmp format ready to be written on disk.

decodeBitmap :: ByteString -> Either String DynamicImage

Try to decode a bitmap image. Right now this function can output the following pixel types :

• PixelRGB8

encodeDynamicBitmap :: DynamicImage -> Either String ByteString

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

• RGB8
• RGBA8
• Y8

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

Write a dynamic image in a .bmp image file if possible. The same restriction as encodeDynamicBitmap apply.

Jpeg handling

readJpeg :: FilePath -> IO (Either String DynamicImage)

Try to load a jpeg file and decompress. The colorspace is still YCbCr if you want to perform computation on the luma part. You can convert it to RGB using colorSpaceConversion

decodeJpeg :: ByteString -> Either String DynamicImage

Try to decompress a jpeg file and decompress. The colorspace is still YCbCr if you want to perform computation on the luma part. You can convert it to RGB using colorSpaceConversion

This function can output the following pixel types :

• PixelY8
• PixelYCbCr8

Png handling

class PngSavable a where

Encode an image into a png if possible.

Methods

encodePng :: Image a -> ByteString

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

Instances

PngSavable PixelRGBA8

PngSavable PixelRGB8

PngSavable Pixel8

readPng :: FilePath -> IO (Either String DynamicImage)

Helper function trying to load a png file from a file on disk.

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
• PixelYA8
• PixelRGB8
• PixelRGBA8

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 :

• RGB8
• RGBA8
• Y8

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

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

Image types and pixel types

Image

data Image a

Image or pixel buffer, the coordinates are assumed to start from the upper-left corner of the image, with the horizontal position first, then the vertical one.

data DynamicImage

Type allowing the loading of an image with different pixel structures

Constructors

ImageY8 (Image Pixel8)

A greyscale image.

ImageYA8 (Image PixelYA8)

An image in greyscale with an alpha channel.

ImageRGB8 (Image PixelRGB8)

An image in true color.

ImageRGBA8 (Image PixelRGBA8)

An image in true color and an alpha channel.

ImageYCbCr8 (Image PixelYCbCr8)

An image in the colorspace used by Jpeg images.

Pixels

class Serialize a => Pixel a where

Typeclass used to query a type about it's properties regarding casting to other pixel types

Methods

canPromoteTo :: a -> PixelType -> Bool

Tell if a pixel can be converted to another pixel, the first value should not be used, and undefined can be used as a valid value.

componentCount :: a -> Int

Return the number of component of the pixel

pixelBaseIndex :: Image a -> Int -> Int -> Int

Calculate the index for the begining of the pixel

mutablePixelBaseIndex :: MutableImage s a -> Int -> Int -> Int

Calculate theindex for the begining of the pixel at position x y

promotionType :: a -> PixelType

Return the constructor associated to the type, again the value in the first parameter is not used, so you can use undefined

pixelAt :: Image a -> Int -> Int -> a

Extract a pixel at a given position, (x, y), the origin is assumed to be at the corner top left, positive y to the bottom of the image

readPixel :: MutableImage s a -> Int -> Int -> ST s a

Same as pixelAt but for mutable images.

writePixel :: MutableImage s a -> Int -> Int -> a -> ST s ()

Write a pixel in a mutable image at position x y

Instances

Pixel PixelRGBA8

Pixel PixelYCbCr8

Pixel PixelRGB8

Pixel PixelYA8

Pixel Pixel8

type Pixel8 = Word8

Simple alias for greyscale value in 8 bits.

data PixelYA8

Pixel type storing Luminance (Y) and alpha information on 8 bits. Value are stored in the following order :

• Luminance
• Alpha

Constructors

PixelYA8 !Word8 !Word8

Instances

Serialize PixelYA8

Pixel PixelYA8

ColorConvertible PixelYA8 PixelRGBA8

ColorConvertible PixelYA8 PixelRGB8

ColorConvertible Pixel8 PixelYA8

data PixelRGB8

Pixel type storing classic pixel on 8 bits Value are stored in the following order :

• Red
• Green
• Blue

Constructors

PixelRGB8 !Word8 !Word8 !Word8

Instances

Serialize PixelRGB8

Pixel PixelRGB8

PngSavable PixelRGB8

BmpEncodable PixelRGB8

ColorSpaceConvertible PixelYCbCr8 PixelRGB8

ColorConvertible PixelRGB8 PixelRGBA8

ColorConvertible PixelYA8 PixelRGB8

ColorConvertible Pixel8 PixelRGB8

data PixelRGBA8

Pixel type storing a classic pixel, with an alpha component. Values are stored in the following order

• Red
• Green
• Blue
• Alpha

Constructors

PixelRGBA8 !Word8 !Word8 !Word8 !Word8

Instances

Serialize PixelRGBA8

Pixel PixelRGBA8

PngSavable PixelRGBA8

BmpEncodable PixelRGBA8

ColorConvertible PixelRGB8 PixelRGBA8

ColorConvertible PixelYA8 PixelRGBA8

ColorConvertible Pixel8 PixelRGBA8

data PixelYCbCr8

Pixel storing data in the YCbCr colorspace, value are stored in teh following order :

• Y (luminance)
• Cr
• Cb

Constructors

PixelYCbCr8 !Word8 !Word8 !Word8

Instances

Serialize PixelYCbCr8

Pixel PixelYCbCr8

ColorSpaceConvertible PixelYCbCr8 PixelRGB8