There are two types of graphics images which can be used within Pencil2D, these are bitmapped and vector. I have always used vector based graphics because when I started drawing graphics using computers bitmapped graphics had not been invented.
I don’t have anything against bitmapped graphics. But if you draw a bitmapped image and then want to zoom into a detail within the image, the appearance goes ‘Blocky’. If you don’t have access to a package like Photoshop, this will always be the case. Photoshop costs approx $40 a month for students and $60 per month for professionals, this is a lot of money unless your employer pays for it.
You can avoid the problem, by drawing your image much larger than that defined by your screen resolution. You can reduce the size of a graphic without any problems. This is because the mathematics is simple and uses averages. Enlargement requires trend line analysis in 2 dimensions, which requires complex calculations and very powerful hardware.
If you draw your image using vector methods, Enlargement or shining an image is no problem and neither is zooming in or zooming out!
You can design your vector image using Inkscape and then export this in a large resolution as a .PNG image, which you then import into Pencil2D to acheive the result.
There is another technique developed after vector based graphics and before modern bitmapped graphics, this is sprites. These were initially single user defined characters and were displayed on screen in place of characters. These were initially used within computer games, but multiple sprites can be used in animation, an example is shown below.
These sprites were developed using Inkscape, I.e. vector drawings. These were then exported as high resolution bitmapped images in .PNG format. These were then imported into a bitmapped layer in Pencil2D.