iOS UIImageView按比例缩小图像会在iPad 2上生成别名图像 [英] iOS UIImageView scaling image down produces aliased image on iPad 2

问题描述

我正在使用UIImageView显示图像的缩略图，然后可以选择以全尺寸查看。 UIImageView的内容模式设置为宽高比适合。

I am using UIImageView to display thumbnails of images that can then be selected to be viewed at full size. The UIImageView has its content mode set to aspect fit.

图像通常从大约500px x 500px缩小到100px x 100px。在视网膜iPad上，它们显示得非常好，而在iPad2上，它们的颜色非常混乱，直到尺寸接近原始图像尺寸。

The images are usually scaled down from around 500px x 500px to 100px x 100px. On the retina iPad they display really well while on the iPad2 they are badly aliased until the size gets closer to the native image size.

示例：

原始图像

Retina iPad渲染为100px x 100px

Retina iPad rendering at 100px x 100px

iPad 2渲染速度为100px x 100px

iPad 2 rendering at 100px x 100px

iPad 2和新iPad之间的区别可能只是屏幕分辨率，或者可能是GPU更适合缩放图像。无论哪种方式，iPad 2渲染都非常差。

The difference between iPad 2 and new iPad might just be the screen resolution or could be that the GPU is better equipped to scale images. Either way, the iPad 2 rendering is very poor.

我首先尝试通过创建新的上下文来减小图像大小，将插值质量设置为高并绘制图像进入上下文。在这种情况下，两张iPad上的图像看起来都很好。

I have tried first reducing the image size by creating a new context, setting the interpolation quality to high and drawing the image into the context. In this case, the image looks fine on both iPads.

在我继续图像复制/调整大道之前，我想检查一下我没有更简单的东西失踪。我很欣赏UIImage不是可以扩展的，但我的印象是UIImageView可以处理扩展，但目前它似乎没有做好缩小的工作。我错过了什么（如果有的话）？

Before I continue down the image copy/resize avenue, I wanted to check there wasn't something simpler I was missing. I appreciate that UIImage isn't there to be scaled but I was under the impression UIImageView was there to handle scaling but at the moment it doesn't seem to be doing a good job scaling down. What (if anything) am I missing?

更新：注意：渲染/调整大小的图像上的阴影会添加到代码中。禁用此功能对缩放的质量没有任何影响。

Update: Note: The drop shadow on the rendered / resized images is added in code. Disabling this made no difference to the quality of the scaling.

推荐答案

我试过的另一种方法似乎确实在改进是设置minificationFilter：

Another approach I've tried that does seem to be improving things is to set the minificationFilter:

[imageView.layer setMinificationFilter:kCAFilterTrilinear]

质量肯定有所改善，我没有发现性能受到影响。

The quality is certainly improved and I haven't noticed a performance hit.

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