What is the format of the transparent base?

It is in PNG format, and its making and saving methods are as follows:

1. Open Mito Xiu Xiu to import pictures, as shown in the following figure:

2. Click "Plotter Pen" in the second line, as shown in the following figure:

3. Choose one style according to the actual situation of the picture, as shown in the following figure:

4. Use the matting pen to draw a line on the image that needs to be preserved in the picture, as shown in the following figure:

5. Click Save As Transparent Background at the bottom, as shown in the figure below:

6. Finally, choose to save in PNG format, as shown in the following figure: