diff --git a/SDWebImage/SDWebImageImageIOCoder.m b/SDWebImage/SDWebImageImageIOCoder.m
index 95b25b08..8f31e974 100644
--- a/SDWebImage/SDWebImageImageIOCoder.m
+++ b/SDWebImage/SDWebImageImageIOCoder.m
@@ -267,14 +267,14 @@ static const CGFloat kDestSeemOverlap = 2.0f;   // the numbers of pixels to over
         CGSize sourceResolution = CGSizeZero;
         sourceResolution.width = CGImageGetWidth(sourceImageRef);
         sourceResolution.height = CGImageGetHeight(sourceImageRef);
-        float sourceTotalPixels = sourceResolution.width * sourceResolution.height;
+        CGFloat sourceTotalPixels = sourceResolution.width * sourceResolution.height;
         // Determine the scale ratio to apply to the input image
         // that results in an output image of the defined size.
         // see kDestImageSizeMB, and how it relates to destTotalPixels.
-        float imageScale = kDestTotalPixels / sourceTotalPixels;
+        CGFloat imageScale = sqrt(kDestTotalPixels / sourceTotalPixels);
         CGSize destResolution = CGSizeZero;
-        destResolution.width = (int)(sourceResolution.width*imageScale);
-        destResolution.height = (int)(sourceResolution.height*imageScale);
+        destResolution.width = (int)(sourceResolution.width * imageScale);
+        destResolution.height = (int)(sourceResolution.height * imageScale);
         
         // device color space
         CGColorSpaceRef colorspaceRef = SDCGColorSpaceGetDeviceRGB();