更改UIImage（而不是UIImageView）的透明度

Question

I am using AVAssetWriterInputPixelBufferAdaptor to create a video from an array of UIImage's, and i want to change the transition from one image to another in different forms of animations(much like a slide show ... actually exactly like a slideshow).

One of these transitional styles is fade out. since im writing UIImages like so ..

    UIImage *image = imageView.image;
    UIImage *resizedImage = [ICVideoViewController imageWithImage:image scaledToSize:CGSizeMake(640, 480)];
    CGImageRef img = [resizedImage CGImage];
    CVPixelBufferRef buffer = [ICVideoViewController pixelBufferFromCGImage:img size:CGSizeMake(640, 480)];

    [adaptor appendPixelBuffer:buffer withPresentationTime:CMTimeMake(i, 1)];

I would like to know if it is possible (without having to manually manipulate the pixels) to achieve this .. ?

Answer 1

I dont know how you are creating image in imagawithimage function of your view controller.

If you are using CGContext to scale image then use CGContextSetAlpha() before CGContextDrawImage() .

If not you can do one more thing, no doubt you will need to code few more lines for that but this can be one way :

CGSize size = [self size];
int width = size.width;
int height = size.height;

// the pixels will be painted to this array
uint32_t *pixels = (uint32_t *) malloc(width * height * sizeof(uint32_t));

// clear the pixels so any transparency is preserved
memset(pixels, 0, width * height * sizeof(uint32_t));

CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

// create a context with RGBA pixels
CGContextRef context = CGBitmapContextCreate(pixels, width, height, 8, width * sizeof(uint32_t), colorSpace, 
                                             kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedLast);

// paint the bitmap to our context which will fill in the pixels array
CGContextSetAlpha(context, 0.5);
CGContextDrawImage(context, CGRectMake(0, 0, width, height), [self CGImage]);
CGImageRef image = CGBitmapContextCreateImage(context);

CGContextRelease(context);
CGColorSpaceRelease(colorSpace);
free(pixels);

Answer 2

How about blending the two images you're transitioning?

See the following thread: blend two uiimages based on alpha/transparency of top image