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The Image module

exception Out_of_image

exception for illegal point access

exception Wrong_image_type

exception for illegal internal image type

exception Wrong_file_type

exception for unsupported image FILE format

Generic image

type t =
   | Index8 of Index8.t
   | Rgb24 of Rgb24.t
   | Index16 of Index16.t
   | Rgba32 of Rgba32.t
   | Cmyk32 of Cmyk32.t

Generic image type


Colors: the copies of color.mli

type rgb = Color.rgb = { mutable r: int; mutable g: int; mutable b: int }
type rgba = Color.rgba = { color: rgb; mutable alpha: int }
type cmyk = Color.cmyk = 
    { mutable c : int; mutable m : int; mutable y : int; mutable k : int }
type map = Color.map = {
    mutable max: int;

maximum number allowed in the color map (-1 = unlimited)

: rgb array

Image file format

Image formats

type format = 
   | Gif
   | Bmp
   | Jpeg
   | Tiff  
   | Png
   | Xpm
   | Ppm
   | Ps

Image file name extensions

functions for filename extensions

val extension : format -> string

returns the corresponding extension "gif", "bmp" etc. for given format

val guess_format : string -> format

returns the image format guessed from the file extension of a given file name

lower interface

val get_extension : string -> string * string

val guess_extension : string -> format

Image file header informations

type colormodel = Info.colormodel =
   | Gray | RGB | Index | GrayA | RGBA

Infos attached to bitmaps

type info = Info.info =
   | Info_DPI of float (* dot per inch *)
   | Info_BigEndian | Info_LittleEndian (* endianness of image file *)
   | Info_ColorModel of colormodel (* color model of image file *)
   | Info_Depth of int (* Image bit depth *)
   | Info_Corrupted (* For corrupted PNG files *)

info query

val dpi : info list -> float option 

Image file header

type header = {
     header_width : int;
     header_height : int;
     header_infos : info list

val file_format : string -> format * header

file_format filename reads the header of image file filename and returns its format and some useful information found in the header (ex. width, height). file_format does not read image contents, but just quickly returns file header information.

file_format does not depend on any external libraries

Image file I/O options

Load options

type load_option =
   | Load_Progress of (float -> unit) (* For progress meters *)
   | Load_Resolution of float * float (* Pixel/Inch for rasterization of PS *)

Save options

type save_option =
   | Save_Quality of int (* Save quality for Jpeg compression *)
   | Save_Progress of (float -> unit) (* For progress meters *)
   | Save_Interlace (* Interlaced Gif *)

Option queries

val load_progress : load_option list -> (float -> unit) option

val load_resolution : load_option list -> (float * float) option

val save_progress : save_option list -> (float -> unit) option

val save_interlace : save_option list -> bool

val save_quality : save_option list -> int option

The type for methods of image file formats

type format_methods = {
    check_header: (string -> header);
    load: (string -> load_option list -> t) option;
    save: (string -> save_option list -> t -> unit) option;

Generic image manupilation

val add_methods : format -> format_methods -> unit

If you write new drivers for some image format, use this function to register their loading/saving functions into the libaray

val load : string -> load_option list -> t

load filename options read the header of an image file filename, loads the image by calling corresponding loading method, and returns it. If the file format is not supported by the library, a Wrong_file_type exception will be raised. You can specify loading options in options such as progressive meter function.

val save : string -> format -> save_option list -> t -> unit

save filename format options image saves image into a file filename in the format format. You can specify some saving parameters options. Some options are specific to some image formats and do not work with the others.

val size : t -> int * int

Returns size (width and height) of image

val destroy : t -> unit

Free the image. If you turn on image swapping (see bitmap.mli), you need to call this function explicitly to tell the library that this image is no longer used.

val blit : t -> int -> int -> t -> int -> int -> int -> int -> unit

blit src sx sy dst dx dy width height copies the rectangle region of src at (sx,sy)-(sx+width-1,sy+height-1) to dst, at (dx,dy)-(dx+width-1,dy+height-1)

Image representation module

Each image representation module must contain these types and functions, at least

 type T = sig
  type t
  type elt

  val create : int -> int -> t

create width height creates an image of the size (width x height)

  val destroy : t -> unit

destroy image frees the memory and swap files of image You have to call this function explicitly if you turn on image swapping (See bitmap.mli).

  val get : t -> int -> int -> elt
  val set : t -> int -> int -> elt -> unit

get image x y and set image x y v reads/writes the pixel information at (x,y) of image. If (x,y) is out of the image, they raise Out_of_image exception.

  val unsafe_get : t -> int -> int -> elt
  val unsafe_set : t -> int -> int -> elt -> unit

unsafe_get and unsafe_set are the same functions as get and set, but they lack the image region checks. So it is fast. But you have to use them with being sure that the specified point is in the image. Otherwise the result is unknown, and sometimes a runtime error occurs.

  val sub : t -> int -> int -> int -> int -> t

sub dst x y width height returns sub-bitmap of dst, at (x,y)-(x+width-1,y+height-1).

  val blit : t -> int -> int -> t -> int -> int -> int -> int -> unit

blit src sx sy dst dx dy width height copies the rectangle region of src at (sx,sy)-(sx+width-1,sy+height-1) to dst, at (dx,dy)-(dx+width-1,dy+height-1)


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