diff --git a/SDWebImage/Core/SDImageIOAnimatedCoder.m b/SDWebImage/Core/SDImageIOAnimatedCoder.m
index b1bd1b24..e5247cb1 100644
--- a/SDWebImage/Core/SDImageIOAnimatedCoder.m
+++ b/SDWebImage/Core/SDImageIOAnimatedCoder.m
@@ -499,7 +499,9 @@ static NSString * kSDCGImageDestinationRequestedFileSize = @"kCGImageDestination
     CGFloat pixelWidth = (CGFloat)CGImageGetWidth(imageRef);
     CGFloat pixelHeight = (CGFloat)CGImageGetHeight(imageRef);
     CGFloat finalPixelSize = 0;
-    if (maxPixelSize.width > 0 && maxPixelSize.height > 0 && pixelWidth > maxPixelSize.width && pixelHeight > maxPixelSize.height) {
+    BOOL encodeFullImage = maxPixelSize.width == 0 || maxPixelSize.height == 0 || pixelWidth == 0 || pixelHeight == 0 || (pixelWidth <= maxPixelSize.width && pixelHeight <= maxPixelSize.height);
+    if (!encodeFullImage) {
+        // Thumbnail Encoding
         CGFloat pixelRatio = pixelWidth / pixelHeight;
         CGFloat maxPixelSizeRatio = maxPixelSize.width / maxPixelSize.height;
         if (pixelRatio > maxPixelSizeRatio) {
diff --git a/SDWebImage/Core/SDImageIOCoder.m b/SDWebImage/Core/SDImageIOCoder.m
index 7149b444..7b5b4a8a 100644
--- a/SDWebImage/Core/SDImageIOCoder.m
+++ b/SDWebImage/Core/SDImageIOCoder.m
@@ -252,10 +252,12 @@ static NSString * kSDCGImageDestinationRequestedFileSize = @"kCGImageDestination
     }
     CGFloat pixelWidth = (CGFloat)CGImageGetWidth(imageRef);
     CGFloat pixelHeight = (CGFloat)CGImageGetHeight(imageRef);
-    if (maxPixelSize.width > 0 && maxPixelSize.height > 0 && pixelWidth > maxPixelSize.width && pixelHeight > maxPixelSize.height) {
+    CGFloat finalPixelSize = 0;
+    BOOL encodeFullImage = maxPixelSize.width == 0 || maxPixelSize.height == 0 || pixelWidth == 0 || pixelHeight == 0 || (pixelWidth <= maxPixelSize.width && pixelHeight <= maxPixelSize.height);
+    if (!encodeFullImage) {
+        // Thumbnail Encoding
         CGFloat pixelRatio = pixelWidth / pixelHeight;
         CGFloat maxPixelSizeRatio = maxPixelSize.width / maxPixelSize.height;
-        CGFloat finalPixelSize;
         if (pixelRatio > maxPixelSizeRatio) {
             finalPixelSize = MAX(maxPixelSize.width, maxPixelSize.width / pixelRatio);
         } else {