Re: Using PNG_IO to create a file.

["Jeff C," <nolongersafeto@userealemailsniff.com>]

"Ron Baldwin" <re(nospam)baldwin@adelphia.net> wrote in message
news:bV2fb.1204$qj6.1035959@news1.news.adelphia.net...
> I need to read .PNG format graphics images from a file, process the image
as
> a two-dimensional array, then write the processed image out to a  new
file.
>
> I have used the PNG_IO package to read data from files, but I can't figure
> out how to get the data from a two-dimensional array to the
Write_PNG_Type_?
> output procedures.
>
> Does anyone have some examples of such an operation?


There is an example in the png_test.adb file that ships with png_io.


You just need to instantiate one of the Write_PNG_Type_X procedures with the
appropriate
parameters.

Now I suspect you looked at this a little already so I am probably telling
you things you already know.

Lets look at an example. The spec for one of the procedures is

 generic
    type Image_Handle is limited private;
    type Sample       is range <>;
    with function Grey_Sample(I    : Image_Handle;
                              R, C : Coordinate) return Sample;
  procedure Write_PNG_Type_0(Filename  : in String;
                             I         : in Image_Handle;
                             X, Y      : in Dimension;
                             Bit_Depth : in Depth   := Eight;
                             Interlace : in Boolean := False;
                             Ancillary : in Chunk_List := Null_Chunk_List);

This is for a greyscale image which of course is the simplest case...So you
need to write a function that takes in
three parameter types. One should be the type of your 2d array, the other
two are the index values to the array and finally the function should return
the value at the row and column passed to it.

So, for example assume you created a 2-d array like

   type My_Pixel_Type is range 0 .. 100;

   type Cool_Picture_Type is array (Coordinate range 0 .. 9, Coordinate
range 0 .. 19) of My_Pixel_Type;

   and you had a variable
   Picture : Cool_Picture_Type

   that you had read your data into

   you need to write

   function Get_Picture_Pixel(From_Array : in Cool_Picture_Type;
                                            Row, Column : in Coordinate)
return Natural;

   and simply implement it as


   function Get_Picture_Pixel(From_Array : in Cool_Picture_Type;
                                            Row, Column : in Coordinate)
return Natural is

  begin
     return From_Array(Row, Column);
  end Get_Picture_Pixel;



To create a write procedure that uses your function you would do

   procedure Write_Cool_Picture is new Write_PNG_Type_0
      (Image_Handle => Cool_Picture_Type;
        Sample            => My_Pixel_Type,
        Grey_Sample  => Get_Picture_Pixel);



  You could then use the new procedure you created to write a file
containing the data from the Picture by doing

     Write_Cool_Picture(Filename => "adarules.png",
                                     I             => Picture,
                                     X            => Picture'length(2),
                                     Y            => Picture'length(1));


And that's it.


Now obviously the stuff above is not in the order to feed to a compiler.
Quite possibly I goofed on a few
syntax elements and/or swaped rows and columns someplace....

But since this seemed more like a basic programming question that is
somewhat answered by the code I hoped
that presenting it in this format would be more useful than yet another
example like in the test driver.