Get the image size of a JPG, GIF and PNG image f… in delphi

// Get the image size of a JPG, GIF and PNG image file

unit ImgSize;

interface

uses Classes;

procedure GetJPGSize(const sFile: string; var wWidth, wHeight: Word);
procedure GetPNGSize(const sFile: string; var wWidth, wHeight: Word);
procedure GetGIFSize(const sGIFFile: string; var wWidth, wHeight: Word);

implementation

uses SysUtils;

function ReadMWord(f: TFileStream): Word;
type
TMotorolaWord = record
case Byte of
0: (Value: Word);
1: (Byte1, Byte2: Byte);
end;
var
MW: TMotorolaWord;
begin
{ It would probably be better to just read these two bytes in normally }
{ and then do a small ASM routine to swap them. But we aren’t talking }
{ about reading entire files, so I doubt the performance gain would be }
{ worth the trouble. }
f.read(MW.Byte2, SizeOf(Byte));
f.read(MW.Byte1, SizeOf(Byte));
Result := MW.Value;
end;

procedure GetJPGSize(const sFile: string; var wWidth, wHeight: Word);
const
ValidSig: array[0..1] of Byte = ($FF, $D8);
Parameterless = [$01, $D0, $D1, $D2, $D3, $D4, $D5, $D6, $D7];
var
Sig: array[0..1] of byte;
f: TFileStream;
x: integer;
Seg: byte;
Dummy: array[0..15] of byte;
Len: word;
ReadLen: LongInt;
begin
FillChar(Sig, SizeOf(Sig), #0);
f := TFileStream.Create(sFile, fmOpenRead);
try
ReadLen := f.read(Sig[0], SizeOf(Sig));

for x := Low(Sig) to High(Sig) do
if Sig[x] <> ValidSig[x] then ReadLen := 0;

if ReadLen > 0 then
begin
ReadLen := f.read(Seg, 1);
while (Seg = $FF) and (ReadLen > 0) do
begin
ReadLen := f.read(Seg, 1);
if Seg <> $FF then
begin
if (Seg = $C0) or (Seg = $C1) then
begin
ReadLen := f.read(Dummy[0], 3); { don’t need these bytes }
wHeight := ReadMWord(f);
wWidth := ReadMWord(f);
end
else
begin
if not (Seg in Parameterless) then
begin
Len := ReadMWord(f);
f.Seek(Len – 2, 1);
f.read(Seg, 1);
end
else
Seg := $FF; { Fake it to keep looping. }
end;
end;
end;
end;
finally
f.Free;
end;
end;

procedure GetPNGSize(const sFile: string; var wWidth, wHeight: Word);
type
TPNGSig = array[0..7] of Byte;
const
ValidSig: TPNGSig = (137,80,78,71,13,10,26,10);
var
Sig: TPNGSig;
f: tFileStream;
x: integer;
begin
FillChar(Sig, SizeOf(Sig), #0);
f := TFileStream.Create(sFile, fmOpenRead);
try
f.read(Sig[0], SizeOf(Sig));
for x := Low(Sig) to High(Sig) do
if Sig[x] <> ValidSig[x] then Exit;
f.Seek(18, 0);
wWidth := ReadMWord(f);
f.Seek(22, 0);
wHeight := ReadMWord(f);
finally
f.Free;
end;
end;

procedure GetGIFSize(const sGIFFile: string; var wWidth, wHeight: Word);
type
TGIFHeader = record
Sig: array[0..5] of char;
ScreenWidth, ScreenHeight: Word;
Flags, Background, Aspect: Byte;
end;

TGIFImageBlock = record
Left, Top, Width, Height: Word;
Flags: Byte;
end;
var
f: file;
Header: TGifHeader;
ImageBlock: TGifImageBlock;
nResult: integer;
x: integer;
c: char;
DimensionsFound: boolean;
begin
wWidth := 0;
wHeight := 0;

if sGifFile = ” then
Exit;

{$I-}
FileMode := 0; { read-only }
AssignFile(f, sGifFile);
reset(f, 1);
if IOResult <> 0 then
{ Could not open file }
Exit;

{ Read header and ensure valid file. }
BlockRead(f, Header, SizeOf(TGifHeader), nResult);
if (nResult <> SizeOf(TGifHeader)) or (IOResult <> 0) or
(StrLComp(‘GIF’, Header.Sig, 3) <> 0) then
begin
{ Image file invalid }
Close(f);
Exit;
end;

{ Skip color map, if there is one }
if (Header.Flags and $80) > 0 then
begin
x := 3 * (1 shl ((Header.Flags and 7) + 1));
Seek(f, x);
if IOResult <> 0 then
begin
{ Color map thrashed }
Close(f);
Exit;
end;
end;

DimensionsFound := False;
FillChar(ImageBlock, SizeOf(TGIFImageBlock), #0);
{ Step through blocks. }
BlockRead(f, c, 1, nResult);
while (not EOF(f)) and (not DimensionsFound) do
begin
case c of
‘,’: { Found image }
begin
BlockRead(f, ImageBlock, SizeOf(TGIFImageBlock), nResult);
if nResult <> SizeOf(TGIFImageBlock) then
begin
{ Invalid image block encountered }
Close(f);
Exit;
end;
wWidth := ImageBlock.Width;
wHeight := ImageBlock.Height;
DimensionsFound := True;
end;
‘ے’: { Skip }
begin
{ NOP }
end;
{ nothing else. just ignore }
end;
BlockRead(f, c, 1, nResult);
end;
Close(f);
{$I+}
end;

end.