文件格式

此分类介绍图像文件格式。虽然大多数文件格式的信息可以在维基百科上查阅，但它不一定能说清楚这些格式的用途和各自的优缺点。

在这个分类中我们会尽可能用一种初学者易于理解的方式来对此进行说明。

一般而言，关于文件格式，人们会关注下列特性：

压缩

压缩指的是某种文件格式以尽可能少的数据来描述图像的手段，以便在不损失画质的前提下尽可能减小文件体积。

我们通常会发现占用磁盘空间较少的文件格式要么有损画质，要么需要计算机花费大量时间去演算图像的结果。

Vector file-formats like SVG are a typical example of the latter. They are really small because the technology used to create them is based on mathematics, so it only stores maths-variables and can achieve very high quality. The downside is that the computer needs to spend a lot of time thinking about how it should look, and sometimes different programs have different ways of interpreting the values. Furthermore, vector file-formats imply vector graphics, which is a very different way of working than Krita is specialized in.

Lossy file formats, like JPG or WebP are an example of small on disk, but lowering the quality, and are best used for very particular types of images. Lossy thus means that the file format plays fast and loose with describing your image to reduce filesize.

Non-lossy or lossless formats, like PNG, GIF or BMP are in contrast, much heavier on disk, but much more likely to retain quality.

Then, there’s proper working file formats like Krita’s KRA, Gimp’s XCF, Photoshop’s PSD, but also interchange formats like ORA and EXR. These are the heaviest on the hard-drive and often require special programs to open them up, but on the other hand these are meant to keep your working environment intact, and keep all the layers and guides in them.

元数据

Metadata is the ability of a file format to contain information outside of the actual image contents. This can be human readable data, like the date of creation, the name of the author, a description of the image, but also computer readable data, like an ICC profile which tells the computer about the qualities of how the colors inside the file should be read.

开放性

这是一个比较特别的性质，但它会影响文件打开和恢复的难易程度，也会影响该文件格式受支持的广泛程度。

Most internal file formats, like PSD are completely closed, and it’s really difficult for human outsiders to recover the data inside without opening Photoshop. Other examples are camera raw files which have different properties per camera manufacturer.

SVG 作为一种矢量文件格式，则是一个完全相反的极端。随便一个文本编辑器都可以打开它们进行编辑。

Most formats are in-between, and thus there’s also a matter of how widely supported the format is. JPG and PNG cannot be read or edited by human eyes, but the vast majority of programs can open them, meaning the owner has easy access to them.

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