iOS-WebP

Most apps nowadays enhance user experience with the use of images, and one of the issues I've noticed with that is the amount of time it takes to load an image. (Not everyone has the luxury of a fast connection)

Google's WebP image format offers better compression compared to PNG or JPEG, allowing apps to send/retrieve images with smaller file sizes, reducing request times and hopefully provide a better user experience.

Getting Started

The CocoaPods Way

pod 'iOS-WebP', '0.5'

Usage

Don't forget to #import <iOS-WebP/UIImage+WebP.h>. There are 3 methods in iOS-WebP, converting images to WebP format, converting images from WebP format, and setting an image's transparency.

+ (void)imageToWebP:(UIImage *)image quality:(CGFloat)quality alpha:(CGFloat)alpha preset:(WebPPreset)preset
    completionBlock:(void (^)(NSData *result))completionBlock
       failureBlock:(void (^)(NSError *error))failureBlock;

+ (void)imageWithWebP:(NSString *)filePath
      completionBlock:(void (^)(UIImage *result))completionBlock
         failureBlock:(void (^)(NSError *error))failureBlock;

- (UIImage *)imageByApplyingAlpha:(CGFloat)alpha;

Encoding and decoding of images are done in the background thread and results returned in the completion block on the main thread so as not to lock the main thread, allowing the UI to be updated as needed.

Converting To WebP

// quality value is [0, 100]
// alpha value is [0, 1]
[UIImage imageToWebP:[UIImage imageNamed:@"demo.jpg"] quality:quality alpha:alpha preset:WEBP_PRESET_DEFAULT completionBlock:^(NSData *result) {
  NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
  NSString *webPPath = [paths[0] stringByAppendingPathComponent:@"image.webp"];
  if (![result writeToFile:webPPath atomically:YES]) {
    NSLog(@"Failed to save file");
  }
} failureBlock:^(NSError *error) {
  NSLog(@"%@", error.localizedDescription);
}];

WebPPreset possible values

• WEBP_PRESET_DEFAULT (default preset)
• WEBP_PRESET_PICTURE (digital picture, like portrait, inner shot)
• WEBP_PRESET_PHOTO (outdoor photograph, with natural lighting)
• WEBP_PRESET_DRAWING (hand or line drawing, with high-contrast details)
• WEBP_PRESET_ICON (small-sized colorful images)
• WEBP_PRESET_TEXT (text-like)

Config block

If you need to fine tune the performance of the encoding algorithm you can specify overrides to the preset in a config block.

// quality value is [0, 100]
// alpha value is [0, 1]
[UIImage imageToWebP:[UIImage imageNamed:@"demo.jpg"] quality:quality alpha:alpha
 preset:WEBP_PRESET_DEFAULT
 configBlock:^(WebPConfig *config) {
    config->sns_strength = 50.0f;
    config->filter_strength = 0.0f;
    config->method = 2;
    config->preprocessing = 0;
    config->filter_sharpness = 0;
    config->thread_level = 1;
 }
 completionBlock:^(NSData *result) {
  NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
  NSString *webPPath = [paths[0] stringByAppendingPathComponent:@"image.webp"];
  if (![result writeToFile:webPPath atomically:YES]) {
    NSLog(@"Failed to save file");
  }
} failureBlock:^(NSError *error) {
  NSLog(@"%@", error.localizedDescription);
}];

All possible config values can be found in encode.h in the WebPConfig stuct.

Converting From WebP

[UIImage imageWithWebP:@"/path/to/file" completionBlock:^(UIImage *result) {
  UIImageView *myImageView = [[UIImageView alloc] initWithImage:result];
}failureBlock:^(NSError *error) {
  NSLog(@"%@", error.localizedDescription);
}];

Setting Image Transparency

//alpha value is [0, 1]
UIImage *transparencyImage = [[UIImage imageNamed:image.jpg] imageByApplyingAlpha:0.5];

Credits

• Based off WebP-iOS-example by Carson McDonald
• imageByApplyingAlpha:alpha function contributed by Dmitry Shmidt
• WebPConfig block contributed by Kasper Weibel Nielsen-Refs and Eugene Scherba
• free_image_data crash fix contributed by Brandon Schlenker and zblackmore
• Memory leak and color changing fix contributed by Sagar Dagdu
• pod libwebp dependency and demo project changes contributed by Emil