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我已经能够调整在 SO 上找到的一些代码，以从我的视图的“屏幕截图”中生成动画 GIF，但结果是不可预测的。GIF 帧有时是完整的图像，完整的帧（“替换”模式，正如 GIMP 标记的那样），其他时候只是与前一层的“差异”（“组合”模式）。

据我所见，当涉及的帧更少和/或更小时，CG 会以“组合”模式写入 GIF，但无法获得正确的颜色。实际上，运动部件的颜色正确，背景是错误的。当 CG 将 GIF 保存为全帧时，颜色还可以。文件大小更大，但是，嘿，显然你不能两全其美。:)

有没有办法：

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

我要做的是（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);

我检查了 ImageBitmapReps，当单独保存为 PNG 时，它们很好。据我了解，颜色表应该由CG处理还是我负责产生抖动的颜色？怎么做？

即使重复制作相同的动画，生成的 GIF 也可能会有所不同。

这是单个 BitmapRep

单帧
（来源：andraz.eu）

这是带有无效颜色的 GIF（“组合”模式） （来源：andraz.eu）组合框架

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1 回答 1

2

我读了你的代码。请在创建 CGImageDestinationRef 时仔细检查“allImages”和“[images count]”。

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);
于 2013-04-10T23:12:10.083 回答