The system uses image objects to represent still pictures taken with the camera on supported devices. To take a picture, use the UIImagePickerController class. To save a picture to the Saved Photos album, use the UIImageWriteToSavedPhotosAlbum function.

系统使用 图像对象 来描述(存储)可支持的设备的相机拍摄的静态图像。如果是想拍照片，使用UIImagePickerController 类。如果是要保存图片到已存储的照片集中，使用UIImageWriteToSavedPhotosAlbum 类。

Images and Memory Management

图像和内存管理

In low-memory situations, image data may be purged from a UIImage object to free up memory on the system. This purging behavior affects only the image data stored internally by the UIImage object and not the object itself. When you attempt to draw an image whose data has been purged, the image object automatically reloads the data from its original file. This extra load step, however, may incur a small performance penalty.

在低内存的情况下，图像数据可能会被从UIImage对象清除来释放系统的内存。这个清除动作仅仅会影响由UIImage对象内部存储的图像数据而不会影响图像对象本身。当你尝试显示一副数据已经被清除的图像，图像对象会自动地从原文件重新载入数据。这个额外的载人呀步骤可能会引起小小的运行问题。(PS:也就是说 内存不够的时候就会清除UIImage对象的数据来是释放内存，要用到图像的时候就重新载入图像)

You should avoid creating UIImage objects that are greater than 1024 x 1024 in size. Besides the large amount of memory such an image would consume, you may run into problems when using the image as a texture in OpenGL ES or when drawing the image to a view or layer. This size restriction does not apply if you are performing code-based manipulations, such as resizing an image larger than 1024 x 1024 pixels by drawing it to a bitmap-backed graphics context. In fact, you may need to resize an image in this manner (or break it into several smaller images) in order to draw it to one of your views.

避免创建大于1024 x 1024的UIImage对象。这种大图像不仅会消耗的大量内存，当使用这种图像作为OpenGL ES的材质或者在视图或者图层上显示这种图像，可能会遇到问题。当执行基于代码的操作时这种图像大小限制是不适用的，比如通过支持位图的图形环境来改变一副大于1024 x 1024像素的图像的大小。事情上，你可能需要用这种方法来改变图像的大小(或者把图像分割成几个更小的图像)以在你的视图上显示图像。

Comparing Images in iOS 8 

对比iOS 8 中的图像处理

The bulk of what an image is lies in its CGImageRef and not in the UIImage object it is wrapped in. As of iOS 8, you can no longer rely on pointer equality to compare cached UIImage objects as the caching mechanism may not return the same UIImage object, but will have cached image data separately. You must use isEqual: to correctly test for equality.

图像的大部分数据存储在它的 CGImageRef 中，而不是包入UIImage对象中。 在iOS 8 中，你不可以再依靠指针相同去比较已缓冲的UIImage对象因为缓冲机制可能不会返回同一个UIImage对象，而是分离地缓存图像数据。一定要使用isEqual:来正确测试相等与否。(PS:我不了解这块内容 翻错了别打我?? 不过好像我什么都不怎么了解啊 你们自己看吧 大部分都不会有错的 )