objective-c – 在Cocoa中创建动画GIF – 定义帧类型

2019年8月4日 133次阅读

我已经能够调整在SO上找到的一些代码,从我的视图的“屏幕截图”中生成一个动画GIF,但结果是不可预测的. GIF帧有时是完整图像,全帧(“替换”模式,如GIMP标记它),其他时间只是前一层的“差异”(“组合”模式).

从我所看到的,当涉及更少和/或更小的帧时,CG将GIF写入“组合”模式,但未能使颜色正确.实际上,运动部件颜色正确,背景错误.
当CG将GIF保存为全帧时,颜色正常.文件大小更大,但是嘿,显然你不可能拥有两全其美. 🙂

有没有办法：

    a) force CG to create "full frames" when saving the GIF
    b) fix the colors (color table?)

我所做的是(ARC模式)：

捕获视图的可见部分

[[scrollView contentView] dataWithPDFInsideRect:[[scrollView contentView] visibleRect]];

将其转换并调整为PNG类型的NSImageBitmapRep

-(NSMutableDictionary*) pngImageProps:(int)quality {
  NSMutableDictionary *pngImageProps;  
  pngImageProps = [[NSMutableDictionary alloc] init];
  [pngImageProps setValue:[NSNumber numberWithBool:NO] forKey:NSImageInterlaced];
  double compressionF = 1;

  [pngImageProps setValue:[NSNumber numberWithFloat:compressionF] forKey:NSImageCompressionFactor];
  return pngImageProps;
}


-(NSData*) resizeImageToData:(NSData*)data toDimX:(int)xdim andDimY:(int)ydim withQuality:(int)quality{
  NSImage *image = [[NSImage alloc] initWithData:data];
  NSRect inRect = NSZeroRect;
  inRect.size = [image size];

  NSRect outRect = NSMakeRect(0, 0, xdim, ydim);
  NSImage *outImage = [[NSImage alloc] initWithSize:outRect.size];

  [outImage lockFocus];
    [image drawInRect:outRect fromRect:inRect operation:NSCompositeCopy fraction:1];
    NSBitmapImageRep* bitmapRep = [[NSBitmapImageRep alloc] initWithFocusedViewRect:outRect];
  [outImage unlockFocus];

  NSMutableDictionary *imageProps = [self pngImageProps:quality];
  NSData* imageData = [bitmapRep representationUsingType:NSPNGFileType properties:imageProps];
  return [imageData copy];
}

获取BitmapReps数组并创建GIF

-(CGImageRef) pngRepDataToCgImageRef:(NSData*)data {
  CFDataRef imgData = (__bridge CFDataRef)data;
  CGDataProviderRef imgDataProvider = CGDataProviderCreateWithCFData (imgData);
  CGImageRef image = CGImageCreateWithPNGDataProvider(imgDataProvider, NULL, true, kCGRenderingIntentDefault);
  return image;
}

////////// create GIF from 

NSArray *images;  // holds all BitmapReps

CGImageDestinationRef destination = CGImageDestinationCreateWithURL((__bridge CFURLRef)[NSURL fileURLWithPath:pot],
                                                                    kUTTypeGIF,
                                                                    allImages,
                                                                    NULL);
// set frame delay
NSDictionary *frameProperties = [NSDictionary
                                 dictionaryWithObject:[NSDictionary
                                                       dictionaryWithObject:[NSNumber numberWithFloat:0.2f]
                                                       forKey:(NSString *) kCGImagePropertyGIFDelayTime]
                                 forKey:(NSString *) kCGImagePropertyGIFDictionary];

// set gif color properties
NSMutableDictionary *gifPropsDict = [[NSMutableDictionary alloc] init];
[gifPropsDict setObject:(NSString *)kCGImagePropertyColorModelRGB forKey:(NSString *)kCGImagePropertyColorModel];
[gifPropsDict setObject:[NSNumber numberWithBool:YES] forKey:(NSString *)kCGImagePropertyGIFHasGlobalColorMap];

// set gif loop
NSDictionary *gifProperties = [NSDictionary
                               dictionaryWithObject:gifPropsDict
                               forKey:(NSString *) kCGImagePropertyGIFDictionary];

// loop through frames and add them to GIF 
for (int i=0; i < [images count]; i++) {
  NSData *imageData = [images objectAtIndex:i];
  CGImageRef imageRef = [self pngRepDataToCgImageRef:imageData];
    CGImageDestinationAddImage(destination, imageRef, (__bridge CFDictionaryRef) (frameProperties));
}

// save the GIF
CGImageDestinationSetProperties(destination, (__bridge CFDictionaryRef)(gifProperties));
CGImageDestinationFinalize(destination);
CFRelease(destination);

我已经检查了ImageBitmapReps,当单独保存为PNG时,它们就可以了.
据我所知,颜色表应该由CG处理,还是我负责产生抖动的颜色？怎么做？

即使重复进行相同的动画,制作的GIF也可能会有所不同.

这是一个BitmapRep

single frame http://andraz.eu/stuff/gif/frame.png

这是带有无效颜色的GIF(“组合”模式)
combined frames http://andraz.eu/stuff/gif/anim2.gif

最佳答案 我读了你的代码.在创建CGImageDestinationRef和“[images count]”时,请仔细检查“allImages”.

以下测试代码工作正常：

NSDictionary *prep = [NSDictionary dictionaryWithObject:[NSDictionary dictionaryWithObject:[NSNumber numberWithFloat:0.2f] forKey:(NSString *) kCGImagePropertyGIFDelayTime] forKey:(NSString *) kCGImagePropertyGIFDictionary];

CGImageDestinationRef dst = CGImageDestinationCreateWithURL((__bridge CFURLRef)(fileURL), kUTTypeGIF, [filesArray count], nil);

for (int i=0;i<[filesArray count];i++)
{
    //load anImage from array
    ...

    CGImageRef imageRef=[anImage CGImageForProposedRect:nil context:nil hints:nil];
    CGImageDestinationAddImage(dst, imageRef,(__bridge CFDictionaryRef)(prep));

}

bool fileSave = CGImageDestinationFinalize(dst);
CFRelease(dst);
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