iphone - 使用 UIImagePickerController 以特定分辨率捕获照片

Question

我想拍一张写着字的A4纸。重要的是，我希望文本可读，但我不希望图像分辨率为 2592x1936 像素或 3264x2448 像素，因为那样太大了。另外，我假设在拍摄后重新缩放照片需要额外的时间，所以我也想避免这种情况。

我们可以在以下品质中进行选择:

UIImagePickerControllerQualityTypeHigh = 0   
UIImagePickerControllerQualityTypeMedium          = 1  default value   
UIImagePickerControllerQualityTypeLow            = 2   
UIImagePickerControllerQualityType640x480         = 3,   
UIImagePickerControllerQualityTypeIFrame1280x720  = 4,   
UIImagePickerControllerQualityTypeIFrame960x540   = 5 

如果我们使用 AVFoundation，我们可以从 this nice table 中选择分辨率(在标题“捕获静止图像”下)。

但是 UIImagePickerController 是否有类似的表格，例如说 UIImagePickerControllerQualityTypeHigh 在 iPhone 3gs 上等于 1920x1080？

Answer 1

UIImagepickerController quality用于视频录制(在 UIImagepickerController 属性“videoQuality”中使用)。

我想如果你想指定确切的照片分辨率应该是多少，你应该使用 AV Foundation 框架而不是 UIImagepickerController。或者如你所说，事后转换图片。

之后调整它的大小(找到 here ):

//  ==============================================================
//  resizedImage
//  ==============================================================
// Return a scaled down copy of the image.  

UIImage* resizedImage(UIImage *inImage, CGRect thumbRect)
{
    CGImageRef          imageRef = [inImage CGImage];
    CGImageAlphaInfo    alphaInfo = CGImageGetAlphaInfo(imageRef);

    // There's a wierdness with kCGImageAlphaNone and CGBitmapContextCreate
    // see Supported Pixel Formats in the Quartz 2D Programming Guide
    // Creating a Bitmap Graphics Context section
    // only RGB 8 bit images with alpha of kCGImageAlphaNoneSkipFirst, kCGImageAlphaNoneSkipLast, kCGImageAlphaPremultipliedFirst,
    // and kCGImageAlphaPremultipliedLast, with a few other oddball image kinds are supported
    // The images on input here are likely to be png or jpeg files
    if (alphaInfo == kCGImageAlphaNone)
        alphaInfo = kCGImageAlphaNoneSkipLast;

    // Build a bitmap context that's the size of the thumbRect
    CGContextRef bitmap = CGBitmapContextCreate(
                NULL,
                thumbRect.size.width,       // width
                thumbRect.size.height,      // height
                CGImageGetBitsPerComponent(imageRef),   // really needs to always be 8
                4 * thumbRect.size.width,   // rowbytes
                CGImageGetColorSpace(imageRef),
                alphaInfo
        );

    // Draw into the context, this scales the image
    CGContextDrawImage(bitmap, thumbRect, imageRef);

    // Get an image from the context and a UIImage
    CGImageRef  ref = CGBitmapContextCreateImage(bitmap);
    UIImage*    result = [UIImage imageWithCGImage:ref];

    CGContextRelease(bitmap);   // ok if NULL
    CGImageRelease(ref);

    return result;
}

希望这对您有所帮助!