The native file format of files that you produce in GIMP is XCF, but this isn't suitable for use elsewhere. When you've finished working on an image in GIMP, you need to save to one of the many different standard formats that GIMP offers.
In the case of graphics for a web page, PNG files are becoming increasingly popular and the steps to produce PNG files in GIMP are very straightforward.
1. Save As Dialog
The first step is to click on the File menu and select the Save as or Save a copy commands. They do much the same thing except that Save as will switch to the new PNG file when saving has completed, while Save a copy will save a PNG but keep the original XCF file open in GIMP.
With the dialog open, you can click on Select File Type, that appears just above the Help button, and from the list of file types that is displayed, select PNG image and click Save.
2. Export File Dialog
If you're saving a file with features that aren't available in PNG files, such as layers, the Export File dialog will open. For most users, using the default options here will be the best option, such as Merge Visible Layers in the case of layered files, and then click the Export button.
3. Save as PNG Dialog
Generally, using the default options is best at this stage, but you can change some settings, such as:
- Interlace will load the PNG progressively within a web page.
- Save background color allows you to specify the background color in the case of the PNG being displayed in a browser that doesn't support variable transparency – the background color in the toolbox is the color specified.
- Save gamma can help end users display colors more accurately, but can generally be safely ignored.
- Save layer offset is also best overlooked.
- Save resolution shouldn't affect display in a web page, but defaults to being saved.
- Compression level is best left at the full setting, 9, as image quality isn't affected.
These simple steps cover saving an image as a PNG in GIMP. These files are well suited to use in web pages that are to be viewed in modern browsers.
Note: Some very old browsers don't fully support PNG files and this can lead to problems displaying some aspects of PNG images, such as lots of colors and variable transparency. If it is important to you that older browsers display your image with minimal problems, you may wish to go to Image > Mode > Indexed and reduce the number of colors to 256, though this may have a marked effect on the appearance of the image.