Keep the information about image's original compressed format, for API which only contains image but not image data to process extra logic

SDWebImage/NSData+ImageContentType.h

@@ -32,11 +32,19 @@ typedef NS_ENUM(NSInteger, SDImageFormat) {
 + (SDImageFormat)sd_imageFormatForImageData:(nullable NSData *)data;
 
 /**
- Convert SDImageFormat to UTType
+ *  Convert SDImageFormat to UTType
-
+ *
- @param format Format as SDImageFormat
+ *  @param format Format as SDImageFormat
- @return The UTType as CFStringRef
+ *  @return The UTType as CFStringRef
  */
 + (nonnull CFStringRef)sd_UTTypeFromSDImageFormat:(SDImageFormat)format;
 
+/**
+ *  Convert UTTyppe to SDImageFormat
+ *
+ *  @param uttype The UTType as CFStringRef
+ *  @return The Format as SDImageFormat
+ */
++ (SDImageFormat)sd_imageFormatFromUTType:(nonnull CFStringRef)uttype;
+
 @end

SDWebImage/NSData+ImageContentType.m

@@ -95,4 +95,27 @@
     return UTType;
 }
 
++ (SDImageFormat)sd_imageFormatFromUTType:(CFStringRef)uttype {
+    if (!uttype) {
+        return SDImageFormatUndefined;
+    }
+    SDImageFormat imageFormat;
+    if (CFStringCompare(uttype, kUTTypeJPEG, 0) == kCFCompareEqualTo) {
+        imageFormat = SDImageFormatJPEG;
+    } else if (CFStringCompare(uttype, kUTTypePNG, 0) == kCFCompareEqualTo) {
+        imageFormat = SDImageFormatPNG;
+    } else if (CFStringCompare(uttype, kUTTypeGIF, 0) == kCFCompareEqualTo) {
+        imageFormat = SDImageFormatGIF;
+    } else if (CFStringCompare(uttype, kUTTypeTIFF, 0) == kCFCompareEqualTo) {
+        imageFormat = SDImageFormatTIFF;
+    } else if (CFStringCompare(uttype, kSDUTTypeWebP, 0) == kCFCompareEqualTo) {
+        imageFormat = SDImageFormatWebP;
+    } else if (CFStringCompare(uttype, kSDUTTypeHEIC, 0) == kCFCompareEqualTo) {
+        imageFormat = SDImageFormatHEIC;
+    } else {
+        imageFormat = SDImageFormatUndefined;
+    }
+    return imageFormat;
+}
+
 @end

SDWebImage/SDWebImageCodersManager.m

@@ -12,6 +12,7 @@
 #ifdef SD_WEBP
 #import "SDWebImageWebPCoder.h"
 #endif
+#import "UIImage+MultiFormat.h"
 
 #define LOCK(lock) dispatch_semaphore_wait(lock, DISPATCH_TIME_FOREVER);
 #define UNLOCK(lock) dispatch_semaphore_signal(lock);
@@ -121,7 +122,9 @@
     UNLOCK(self.codersLock);
     for (id<SDWebImageCoder> coder in coders.reverseObjectEnumerator) {
         if ([coder canDecodeFromData:*data]) {
-            return [coder decompressedImageWithImage:image data:data options:optionsDict];
+            UIImage *decompressedImage = [coder decompressedImageWithImage:image data:data options:optionsDict];
+            decompressedImage.sd_imageFormat = image.sd_imageFormat;
+            return decompressedImage;
         }
     }
     return nil;

SDWebImage/SDWebImageCompat.m

@@ -35,6 +35,7 @@ inline UIImage *SDScaledImageForKey(NSString * _Nullable key, UIImage * _Nullabl
         UIImage *animatedImage = [UIImage animatedImageWithImages:scaledImages duration:image.duration];
         if (animatedImage) {
             animatedImage.sd_imageLoopCount = image.sd_imageLoopCount;
+            animatedImage.sd_imageFormat = image.sd_imageFormat;
         }
         return animatedImage;
     } else {
@@ -57,6 +58,7 @@ inline UIImage *SDScaledImageForKey(NSString * _Nullable key, UIImage * _Nullabl
             }
 
             UIImage *scaledImage = [[UIImage alloc] initWithCGImage:image.CGImage scale:scale orientation:image.imageOrientation];
+            scaledImage.sd_imageFormat = image.sd_imageFormat;
             image = scaledImage;
         }
         return image;

SDWebImage/SDWebImageGIFCoder.m

@@ -81,6 +81,7 @@
         
         animatedImage = [SDWebImageCoderHelper animatedImageWithFrames:frames];
         animatedImage.sd_imageLoopCount = loopCount;
+        animatedImage.sd_imageFormat = SDImageFormatGIF;
     }
     
     CFRelease(source);

SDWebImage/SDWebImageImageIOCoder.m

@@ -11,6 +11,7 @@
 #import "NSImage+WebCache.h"
 #import <ImageIO/ImageIO.h>
 #import "NSData+ImageContentType.h"
+#import "UIImage+MultiFormat.h"
 
 #if SD_UIKIT || SD_WATCH
 static const size_t kBytesPerPixel = 4;
@@ -97,6 +98,7 @@ static const CGFloat kDestSeemOverlap = 2.0f;   // the numbers of pixels to over
     }
     
     UIImage *image = [[UIImage alloc] initWithData:data];
+    image.sd_imageFormat = [NSData sd_imageFormatForImageData:data];
     
     return image;
 }
@@ -146,6 +148,7 @@ static const CGFloat kDestSeemOverlap = 2.0f;   // the numbers of pixels to over
             image = [[UIImage alloc] initWithCGImage:partialImageRef size:NSZeroSize];
 #endif
             CGImageRelease(partialImageRef);
+            image.sd_imageFormat = [NSData sd_imageFormatForImageData:data];
         }
     }
     

SDWebImage/SDWebImageWebPCoder.m

@@ -106,6 +106,7 @@
         }
         WebPDemuxDelete(demuxer);
         CGContextRelease(canvas);
+        staticImage.sd_imageFormat = SDImageFormatWebP;
         return staticImage;
     }
     
@@ -145,6 +146,7 @@
     
     UIImage *animatedImage = [SDWebImageCoderHelper animatedImageWithFrames:frames];
     animatedImage.sd_imageLoopCount = loopCount;
+    animatedImage.sd_imageFormat = SDImageFormatWebP;
     
     return animatedImage;
 }
@@ -215,6 +217,7 @@
 #else
         image = [[UIImage alloc] initWithCGImage:newImageRef size:NSZeroSize];
 #endif
+        image.sd_imageFormat = SDImageFormatWebP;
         CGImageRelease(newImageRef);
         CGContextRelease(canvas);
     }

SDWebImage/UIImage+MultiFormat.h

@@ -15,7 +15,7 @@
  * UIKit:
  * For static image format, this value is always 0.
  * For animated image format, 0 means infinite looping.
- * 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 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.
  * AppKit:
  * NSImage currently only support animated via GIF imageRep unlike UIImage.
  * The getter of this property will get the loop count from GIF imageRep
@@ -23,6 +23,13 @@
  */
 @property (nonatomic, assign) NSUInteger sd_imageLoopCount;
 
+/**
+ * The image format represent the original compressed image data format.
+ * If you don't manually specify a format, this information is retrieve from CGImage using `CGImageGetUTType`, which may return nil for non-CG based image. At this time it will return `SDImageFormatUndefined` as default value.
+ * @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.
+ */
+@property (nonatomic, assign) SDImageFormat sd_imageFormat;
+
 + (nullable UIImage *)sd_imageWithData:(nullable NSData *)data;
 - (nullable NSData *)sd_imageData;
 - (nullable NSData *)sd_imageDataAsFormat:(SDImageFormat)imageFormat;

SDWebImage/UIImage+MultiFormat.m

@@ -7,9 +7,9 @@
  */
 
 #import "UIImage+MultiFormat.h"
-
+#import "NSImage+WebCache.h"
-#import "objc/runtime.h"
 #import "SDWebImageCodersManager.h"
+#import "objc/runtime.h"
 
 @implementation UIImage (MultiFormat)
 
@@ -53,6 +53,28 @@
 }
 #endif
 
+- (SDImageFormat)sd_imageFormat {
+    SDImageFormat imageFormat = SDImageFormatUndefined;
+    NSNumber *value = objc_getAssociatedObject(self, @selector(sd_imageFormat));
+    if ([value isKindOfClass:[NSNumber class]]) {
+        imageFormat = value.integerValue;
+        return imageFormat;
+    }
+    // Check CGImage's UTType, may return nil for non-Image/IO based image
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wunguarded-availability"
+    if (&CGImageGetUTType != NULL) {
+        CFStringRef uttype = CGImageGetUTType(self.CGImage);
+        imageFormat = [NSData sd_imageFormatFromUTType:uttype];
+    }
+#pragma clang diagnostic pop
+    return imageFormat;
+}
+
+- (void)setSd_imageFormat:(SDImageFormat)sd_imageFormat {
+    objc_setAssociatedObject(self, @selector(sd_imageFormat), @(sd_imageFormat), OBJC_ASSOCIATION_RETAIN_NONATOMIC);
+}
+
 + (nullable UIImage *)sd_imageWithData:(nullable NSData *)data {
     return [[SDWebImageCodersManager sharedInstance] decodedImageWithData:data];
 }