checking if uiimage supports the scale parameter for retina display phones (only…

… supported form ios 4 onwards)

@@ -174,11 +174,14 @@ static SDImageCache *instance;
     NSData *imageData = [NSData dataWithContentsOfFile:file];
     if (imageData) {
         UIImage *image = [[[UIImage alloc] initWithData:imageData ] autorelease];
+        if ([[UIScreen mainScreen] respondsToSelector:@selector(scale)]) {
             CGFloat scale = 1.0;
             if ([fileKey hasSuffix:@"@2x.png"] || [fileKey hasSuffix:@"@2x.jpg"]) {
                 scale = 2.0;
             }
-        return [[[UIImage alloc] initWithCGImage:image.CGImage scale:scale orientation:UIImageOrientationUp] autorelease];
+            image = [[[UIImage alloc] initWithCGImage:image.CGImage scale:scale orientation:UIImageOrientationUp] autorelease];
+        }
+        return image;
     }
     return nil;
 }

@@ -131,8 +131,12 @@ NSString *const SDWebImageDownloadStopNotification = @"SDWebImageDownloadStopNot
             scale = 2.0;
         }
         
-        UIImage *image = [[[UIImage alloc] initWithData:imageData ] autorelease];
-        image = [[UIImage alloc] initWithCGImage:image.CGImage scale:scale orientation:UIImageOrientationUp];
+        UIImage *image = [[UIImage alloc] initWithData:imageData ];
+        if ([[UIScreen mainScreen] respondsToSelector:@selector(scale)]) {
+            UIImage *originalImage = image;
+            image = [[UIImage alloc] initWithCGImage:originalImage.CGImage scale:scale orientation:UIImageOrientationUp];
+            [originalImage release];
+        }
 
 #ifdef ENABLE_SDWEBIMAGE_DECODER
         [[SDWebImageDecoder sharedImageDecoder] decodeImage:image withDelegate:self userInfo:nil];