如何在不损失视网膜显示质量的情况下将 UIView 捕获到 UIImage [英] How to capture UIView to UIImage without loss of quality on retina display

问题描述

我的代码在普通设备上运行良好，但在视网膜设备上会产生模糊的图像.

My code works fine for normal devices but creates blurry images on retina devices.

有人知道我的问题的解决方案吗?

Does anybody know a solution for my issue?

+ (UIImage *) imageWithView:(UIView *)view
{
    UIGraphicsBeginImageContext(view.bounds.size);
    [view.layer renderInContext:UIGraphicsGetCurrentContext()];

    UIImage * img = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return img;
}

推荐答案

从使用 UIGraphicsBeginImageContext 切换到 UIGraphicsBeginImageContextWithOptions(如在此页面上).传递 0.0 用于缩放(第三个参数)，您将获得一个缩放因子等于屏幕缩放因子的上下文.

Switch from use of UIGraphicsBeginImageContext to UIGraphicsBeginImageContextWithOptions (as documented on this page). Pass 0.0 for scale (the third argument) and you'll get a context with a scale factor equal to that of the screen.

UIGraphicsBeginImageContext 使用固定比例因子 1.0，因此您实际上在 iPhone 4 上获得与在其他 iPhone 上完全相同的图像.我敢打赌，要么 iPhone 4 在您隐式放大时应用了过滤器，要么只是您的大脑发现它不如周围的一切那么敏锐.

UIGraphicsBeginImageContext uses a fixed scale factor of 1.0, so you're actually getting exactly the same image on an iPhone 4 as on the other iPhones. I'll bet either the iPhone 4 is applying a filter when you implicitly scale it up or just your brain is picking up on it being less sharp than everything around it.

所以，我猜:

#import <QuartzCore/QuartzCore.h>

+ (UIImage *)imageWithView:(UIView *)view
{
    UIGraphicsBeginImageContextWithOptions(view.bounds.size, view.opaque, 0.0);
    [view.layer renderInContext:UIGraphicsGetCurrentContext()];

    UIImage * img = UIGraphicsGetImageFromCurrentImageContext();

    UIGraphicsEndImageContext();

    return img;
}

在 Swift 4 中:

And in Swift 4:

func image(with view: UIView) -> UIImage? {
    UIGraphicsBeginImageContextWithOptions(view.bounds.size, view.isOpaque, 0.0)
    defer { UIGraphicsEndImageContext() }
    if let context = UIGraphicsGetCurrentContext() {
        view.layer.render(in: context)
        let image = UIGraphicsGetImageFromCurrentImageContext()
        return image
    }
    return nil
}

这篇关于如何在不损失视网膜显示质量的情况下将 UIView 捕获到 UIImage的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！