Krita, like other applications that can edit images, has its own "native" image file format, which has the file extension .kra.
Generally, when we save na image in Krita, we will want to save it in two different formats:
First, save in the native format, .kra, which can only be opened in Krita, and will save things only Krita understands, like the layers you created in Krita. This format will be your "project" in Krita, containing everything you did in Krita that Krita is capable of saving. You save this file so that you can edit the project in the future in Krita.
Second, save in a common format, such as JPG or PNG, which can be opened by other programs. For example, Instagram doesn't support Krita's .kra format, so you would need to "export" the image (the "project") from inside of Krita to a common format such as JPG or PNG, so it can be sent to Instagram, or other programs or websites.
How to Save .Kra Files
Let's start by learning how to save to Krita's native format. To do this, follow the following steps:
1: open a random JPG image in Krita.
2: click on File -> Save As... on the menubar. This will open the Save as... dialog for you to select where to save the file. Note that we don't use File -> Save because File -> Save will attempt to overwrite the JPG image we opened, which means we would lose the original data forever, which is bad. Make sure you click Save As... when dealing with image-editing apps like Krita.
3: at the bottom of the dialog, above the OK and Cancel buttons, you'll find a field labelled "File name," and under it a field labelled "Save as type." This "Save as type" label labels a dropdown list button which shows the currently selected type. If you opened a JPG, it should read "JPEG Image (*.jpeg *.jpg *.jpe)" by default. Click on the button to view a list of options.
4: select Krita Document (*.kra) from the dropdown list. It should be at the top. The dropdown list may get too long, in which case scrollbars are shown and the top items aren't visible.
5: type a filename for your project file and click save.
After you have "saved as," you can just save normally next time and it will overwrite the .kra file and not the JPG file you opened in Krita.
How to Export JPG Images
To export a JPG image from Krita, the steps are almost the same as the above.
1: click on File -> Export....
2: select the "JPEG Image (*.jpeg *.jpg *.jpe)" file type, give it a file name, and click OK. A dialog box will appear to configure the JPG codec.
3: the most important part of this new codec is the JPG quality setting. In general, you want a value between 80 and 90. Smaller values produce smaller file sizes, which can be important in some cases, such as when you're creating your own website, but it comes at the cost of really ruining the quality of the image. Meanwhile higher values will make the file bigger, but improvements in quality are likely imperceptible. Click OK to export the file.
Note that the JPG format doesn't support transparency, so if your file has transparent areas, the exported JPG will always have a black background or a background of some other color. You must export as PNG if you want transparency.
How to Export Transparent PNG Images
To export a transparent PNG from Krita, the steps are almost the same as the above. This time we select PNG Image instead of JPEG, and the dialog looks different.
The dialog has a compression level like JPG, but his doesn't really change image quality, because PNG is lossless. All this does is make the computer spend more time optimizing the compression to make the file size smaller.
You must check "Store alpha channel (transparency)" in order to save a PNG file with transparency.
Black Transparent Areas in PNGs
In rare cases, specially if you work with game development, you have a program that uses PNG files and makes use of the alpha channel for something other than transparency. In this case, you'll often run into a problem where an exported PNG file has black areas where the fully transparent pixels are supposed to be.
This occurs because most compositing programs use a technique called pre-multiplied alpha. Essentially what this means is that values of the RGB channels were multiplied by the alpha channel. If alpha is zero (fully transparent), then RGB is always going to be 0, 0, 0 or black, no matter what color it was before multiplying, because anything multiplied by zero is zero.
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