uses
JPEG;

procedure JPEGtoBMP(const FileName: TFileName);
var
jpeg: TJPEGImage;
bmp: TBitmap;
begin
jpeg := TJPEGImage.Create;
try
jpeg.CompressionQuality := 100; {Default Value}
jpeg.LoadFromFile(FileName);
bmp := TBitmap.Create;
try
bmp.Assign(jpeg);
bmp.SaveTofile(ChangeFileExt(FileName, ‘.bmp’));
finally
bmp.Free
end;
finally
jpeg.Free
end;
end;

{
CompressionQuality (default 100):
Set a value between 1..100, depending on your need of quality and
image file size. 1 = Smallest file size, 100 = Best quality.
}