分辨率不变是不可能的，至多100%压缩：
uses ..., Jpeg;
procedure TForm1.Button1Click(Sender: TObject);
var
MyJpg : TJPEGImage;
MyBmp : TBitmap;
begin
MyBmp := TBitmap.Create;
with MyBmp do
try
LoadFromFile('a.bmp');
MyJpg := TJPEGImage.Create;
with MyJpg do
begin
Assign(MyBmp);
CompressionQuality := 100; //压缩的百分比,取值为1..100
Compress;
SaveToFile('b.jpg');//保存图片
Free;
end;
finally
Free;
end;
end;
