function BitmapTo65536(Bitmap: TBitmap): string; //из обычного битмапа в этот формат
var
  i, j, c, p: integer;
  w: word;
begin
  SetLength(Result, Bitmap.Width * Bitmap.Height * 2);
  p := 1;
  for i := 0 to Bitmap.Height - 1 do
  begin
    for j := 0 to Bitmap.Width - 1 do
    begin
      c := Bitmap.Canvas.Pixels[j, i];
      w := ((c shl 8) and $F800) + ((c shr 5) and $07E0) + ((c shr 19) and $1F);
      Result[p] := Chr(w and $FF);
      Result[p + 1] := Chr(w shr 8);
      p := p + 2;
    end;
  end;
end;

procedure TForm1.ConvertANItoBMP(FileName:string; Bitmap:TBitmap;Frame:Integer); //а это чтение
var
tmpbuf:array[0..325000] of word;
x,y,i:integer;
w:word;
begin
AssignFile(Fw,FileName);
Reset(Fw);
//lengthfile:=filesize(Fw);
BlockRead(Fw,tmpbuf,$4b+1);
Bitmap.Width:=tmpbuf[$2] div 256;
Bitmap.Height:=tmpbuf[$3] div 256;
for i:=0 to Frame do BlockRead(Fw,tmpbuf,(Bitmap.Width*Bitmap.Height)*2);
for y:=0 to Bitmap.Height-1 do
  for x:=0 to Bitmap.Width-1 do
    begin
    w:=tmpbuf[y*Bitmap.Width+x];
    Bitmap.Canvas.Pixels[x,y]:=((w and $F800) shr 8)+((w and $07E0) shl 5)+((w and $1F) shl 19);
    end;
CloseFile(Fw);
end;