检测UIImage是PNG还是JPEG？ [英] Detect whether an UIImage is PNG or JPEG?

问题描述

目前通过MonoTouch进行iPhone开发的第一步，我正在玩我从照片库中读取的 UIImage 。

Currently doing my first steps with iPhone development through MonoTouch, I am playing with an UIImage that I read from the photo library.

我想要实现的是获取图像的原始字节数组（ byte [] ）。

What I want to achieve is to get the raw byte array (byte[]) of the image.

我知道MonoTouch中有 UIImageJPEGRepresentation 和 UIImagePNGRepresentation 包装器。我也知道如何使用它们。我不知道的是：

I know that there are the UIImageJPEGRepresentation and UIImagePNGRepresentation wrappers in MonoTouch. I also know how to use them. What I don't know is:

我如何决定调用这两个函数中的哪一个？

How do I decide which of these two functions to call?

即如果原始图像是JPEG图像，我不希望将其作为PNG，而是作为JPEG，反之亦然。

I.e. if the original image is a JPEG image, I do not want to get it as an PNG but also as a JPEG, and vice versa.

有没有办法做这个，或者我错过了一些观点？

Is there a way to do this, or am I missing some points on this?

推荐答案

一旦你有 UIImage ，它能够使用 UIImageJPEGRepresentation 或 UIImagePNGRepresentation 生成JPEG或PNG。原始图像的格式仅在从其创建UIImage时才重要（决定加载它的 CFImage 提供程序）。

Once you have a UIImage, it is capable of producing either a JPEG or PNG using UIImageJPEGRepresentation or UIImagePNGRepresentation. The format of the original image is only important when the UIImage is being created from it (decides which CFImage provider to load it).

如果您的应用或算法对确保将其保存为原始格式很重要，我认为您必须在撰写时保持该信息的使用。我仔细检查过，找不到任何宣传它来自哪种格式的东西。

If it's important to your app or algorithm to ensure you save it as the original format, I think you have to maintain that info to use when your writing it. I double checked and couldn't find anything that advertised what format it came from.

您打算通过 UIImageView 更改图像，还是图片保持不变？如果它没有改变，你只需要UI来选择图像，你能得到文件字节吗？例如，如果您显示图像只是为了选择，然后将它们上传到服务器或其他东西， UIImage 只能用于查看和选择，如果您的数据结构记得它来自哪个文件，你可以从磁盘上取回并上传。如果您在视图中更改文件，那么您或用户需要决定图像的输出（以及jpeg的质量）。

Are you going to change the image through UIImageView or does the image stay unchanged in your experience? If it's not changed and you just need the UI to select the image, could you get to file bytes? For example, if you showed the images just to select and then you upload them to a server or something, the UIImage could only be for viewing and selecting and if your data structure remembers which file it came from, you could get the bits back off disk and upload. If your changing the file in the view, then you or the user needs to decide the output (and if jpeg the quality) of the image.

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