Remove BMP background and convert to trasparent PNG with Delphi - delphi

Question

I have a TBitmap, inside the TBitmap there is load a "map image" (image of a map). This map image have a white background and a lot of black line (no antialising only 2 colors white background and black line).
Now I must do this:
Remove the white background from TBitmap (transparent background and black line);
If possible and only if possible replace black line color with another color;
Save the result as trasparent PNG image;
I don't have idea if these are possible.
Suggestions?
NOTE I want avoid to use 3th part of class or VCL if possible. I can use FreeImage library if need because I just use it on my project. I use Delphi XE3.

Answer 1

Change pixelformat to pf1Bit. Create a palette with 2 entries, change the values of the TPaletteEntry to the desired color value (in the shown exaple to red). Create a TPNGImage, assign the bitmap and set the transparency for the PNG.
implementation
uses pngimage;
{$R *.dfm}
Type
TMyPalette = Packed Record
palVersion : Word;
palNumEntries : Word;
palPalEntry : Array [0..1] of TPaletteEntry;
End;
Procedure ChangeBlackColor(bmp:TBitMap);
var
pal:TMyPalette;
begin
bmp.PixelFormat := pf1Bit;
bmp.HandleType := bmDIB;
With pal Do
Begin
palVersion:=$0300;
palNumEntries:=2;
palPalEntry[0].peRed:= $FF;
palPalEntry[0].peGreen:=$00;
palPalEntry[0].peBlue:= $00;
palPalEntry[0].peFlags:=PC_RESERVED;
palPalEntry[1].peRed:= $FF;
palPalEntry[1].peGreen:=$FF;
palPalEntry[1].peBlue:= $FF;
palPalEntry[1].peFlags:=PC_RESERVED;
End;
bmp.Palette := CreatePalette(pLogPalette(#pal)^)
end;
procedure TForm3.Button1Click(Sender: TObject);
var
png:TPngimage;
bmp:TBitmap;
begin
// sample image
Image1.Canvas.Rectangle(0,0,Image1.Width-1,Image1.Height-1);
Image1.Canvas.Ellipse(1,1,Image1.Width,Image1.Height);
bmp := Image1.Picture.Bitmap;
ChangeBlackColor(bmp);
png:=TPngimage.Create;
try
png.Assign(bmp);
png.TransparentColor := clWhite;
png.Transparent := true;
Image2.Picture.Assign(png);
finally
png.Free;
end;
end;