Use the memory bytes size, instead of pixel size to calculate the memory cost function

SDWebImage/SDAnimatedImage.m

@@ -11,6 +11,8 @@
 #import "SDImageCoder.h"
 #import "SDImageCodersManager.h"
 #import "SDImageFrame.h"
+#import "UIImage+MemoryCacheCost.h"
+#import "objc/runtime.h"
 
 static CGFloat SDImageScaleFromPath(NSString *string) {
     if (string.length == 0 || [string hasSuffix:@"/"]) return 1;
@@ -426,3 +428,31 @@ static NSArray *SDBundlePreferredScales() {
 }
 
 @end
+
+@interface SDAnimatedImage (MemoryCacheCost)
+
+@end
+
+@implementation SDAnimatedImage (MemoryCacheCost)
+
+- (NSUInteger)sd_imageMemoryCost {
+    NSNumber *value = objc_getAssociatedObject(self, @selector(sd_memoryCost));
+    if (value != nil) {
+        return value.unsignedIntegerValue;
+    }
+    
+    CGImageRef imageRef = self.CGImage;
+    if (!imageRef) {
+        return 0;
+    }
+    NSUInteger bytesPerFrame = CGImageGetBytesPerRow(imageRef) * CGImageGetHeight(imageRef);
+    NSUInteger frameCount = 1;
+    if (self.isAllFramesLoaded) {
+        frameCount = self.animatedImageFrameCount;
+    }
+    frameCount = frameCount > 0 ? frameCount : 1;
+    NSUInteger cost = bytesPerFrame * frameCount;
+    return cost;
+}
+
+@end

SDWebImage/SDImageCacheConfig.h

@@ -82,13 +82,14 @@ typedef NS_ENUM(NSUInteger, SDImageCacheConfigExpireType) {
 @property (assign, nonatomic) NSUInteger maxCacheSize;
 
 /**
- * The maximum "total cost" of the in-memory image cache. The cost function is the number of pixels held in memory.
+ * The maximum "total cost" of the in-memory image cache. The cost function is the bytes size held in memory.
+ * @note The memory cost is bytes size in memory, but not simple pixels count. For common ARGB8888 image, one pixel is 4 bytes (32 bits).
  * Defaults to 0. Which means there is no memory cost limit.
  */
 @property (assign, nonatomic) NSUInteger maxMemoryCost;
 
 /**
- * The maximum number of objects the cache should hold.
+ * The maximum number of objects in-memory image cache should hold.
  * Defaults to 0. Which means there is no memory count limit.
  */
 @property (assign, nonatomic) NSUInteger maxMemoryCount;

SDWebImage/UIImage+MemoryCacheCost.h

@@ -11,12 +11,13 @@
 @interface UIImage (MemoryCacheCost)
 
 /**
- The memory cache cost for specify image used by image cache. The cost function is the pixles count held in memory.
+ The memory cache cost for specify image used by image cache. The cost function is the bytes size held in memory.
  If you set some associated object to `UIImage`, you can set the custom value to indicate the memory cost.
  
- For `UIImage`, this method return the single frame pixles count when `image.images` is nil for static image. Retuen full frame pixels count when `image.images` is not nil for animated image.
- For `NSImage`, this method return the single frame pixels count because `NSImage` does not store all frames in memory.
+ For `UIImage`, this method return the single frame bytes size when `image.images` is nil for static image. Retuen full frame bytes size when `image.images` is not nil for animated image.
+ For `NSImage`, this method return the single frame bytes size because `NSImage` does not store all frames in memory.
  @note Note that because of the limitations of categories this property can get out of sync if you create another instance with CGImage or other methods.
+ @note For custom animated class conforms to `SDAnimatedImage`, you can override this getter method in your subclass to return a more proper value instead, which representing the current frames' total bytes.
  */
 @property (assign, nonatomic) NSUInteger sd_memoryCost;
 

SDWebImage/UIImage+MemoryCacheCost.m

@@ -8,14 +8,22 @@
 
 #import "UIImage+MemoryCacheCost.h"
 #import "objc/runtime.h"
+#import "NSImage+Compatibility.h"
 
 FOUNDATION_STATIC_INLINE NSUInteger SDMemoryCacheCostForImage(UIImage *image) {
+    CGImageRef imageRef = image.CGImage;
+    if (!imageRef) {
+        return 0;
+    }
+    NSUInteger bytesPerFrame = CGImageGetBytesPerRow(imageRef) * CGImageGetHeight(imageRef);
+    NSUInteger frameCount;
 #if SD_MAC
-    return image.size.height * image.size.width;
+    frameCount = 1;
 #elif SD_UIKIT || SD_WATCH
-    NSUInteger imageSize = image.size.height * image.size.width * image.scale * image.scale;
-    return image.images ? (imageSize * image.images.count) : imageSize;
+    frameCount = image.images.count > 0 ? image.images.count : 1;
 #endif
+    NSUInteger cost = bytesPerFrame * frameCount;
+    return cost;
 }
 
 @implementation UIImage (MemoryCacheCost)