Chapter 6.  Getting images out of GIMP

Table of Contents

1. Files
1.1. Saving Images
1.2. Saving Files
2. Preparing your Images for the Web
2.1. Images with an Optimal Size/Quality Ratio
2.2. Reducing the File Size Even More
2.3. Saving Images with Transparency

1.  Files

The GIMP is capable of reading and writing a large variety of graphics file formats. With the exception of GIMP's native XCF file type, file handling is done by plug-ins. Thus, it is relatively easy to extend GIMP to new file types when the need arises.

Not all file types are equally good for all purposes. This part of the documentation should help you understand the advantages and disadvantages of each type.

1.1.  Saving Images

When you are finished working with an image, you will want to save the results. (In fact, it is often a good idea to save at intermediate stages too: GIMP is a pretty robust program, but we have heard rumors, possibly apocryphal, that it may have been known on rare and mysterious occasions to crash.) Most of the file formats that GIMP can open, can also be used for saving. There is one file format that is special, though: XCF is GIMP's native format, and is useful because it stores everything about an image (well, almost everything; it does not store “undo” information). Thus, the XCF format is especially suitable for saving intermediate results, and for saving images to be re-opened later in GIMP. XCF files are not readable by most other programs that display images, so once you have finished, you will probably also want to save the image in a more widely used format, such as JPEG, PNG, TIFF, etc.

1.2.  Saving Files

There are several commands for saving images. A list, and information on how to use them, can be found in the section covering the File menu.

GIMP allows you to save the images you create in a wide variety of formats. It is important to realize that the only format capable of saving all of the information in an image, including layers, transparency, etc., is GIMP's native XCF format. Every other format preserves some image properties and loses others. When you save an image, GIMP tries to let you know about this, but basically it is up to you to understand the capabilities of the format you choose.

Figure 6.1.  Example of an Export dialog

Example of an Export dialog

As stated above, there is no file format, with the exception of GIMP's native XCF format, that is capable of storing all the data in a GIMP image. When you ask to save an image in a format that will not completely represent it, GIMP notifies you of this, tells you what kind of information will be lost, and asks you whether you would like to “export” the image in a form that the file type can handle. Exporting an image does not modify the image itself, so you do not lose anything by doing this. See Export file.

[Note] Note

When you close an image (possibly by quitting GIMP), you are warned if the image is "dirty"; that is, if it has been changed without subsequently being saved. Saving an image in any file format will cause the image to be considered "not dirty", even if the file format does not represent all of the information from the image.