(Redirected from Raster Graphics)
Bitmap graphics, also called raster graphics or pixel graphics, are graphics stored and rendered as arrays of pixels. Though this method of storage is simpler, it is slower with large images since many pixels need to be stored. For example, the Scratch stage stored as a raster image would be
360*480=172800 pixels, and each pixel has 4 integers associated with it (corresponding to three colors (RGB - red, green, and blue) and a transparency factor).
Usage in Scratch
In Scratch 1.4, and all previous versions, raster graphics were exclusively used. The Scratch 2.0 and 3.0 Paint Editors support both raster and vector graphics, though many features of the Scratch 2.0 and 3.0 user interfaces, notably the blocks, use vector graphics unlike Scratch 1.4's graphics.
Bitmap was the default mode when the user opened the costume editor in Scratch 2.0. However, the default editor is Vector in Scratch 3.0.
Despite the name, Scratch uses the PNG format for bitmap graphics instead of BMP.
Differences Between Versions
As of the release of Scratch 3.0, some features have been changed between Scratch 2.0 and 3.0:
- In Scratch 3.0, the bitmap palette no longer exists. It has been replaced by a slider at the top of the editor in which you change the color, the saturation, and grayscale.
- In Scratch 2.0, one could center a costume with a button, selecting the new center with the mouse-pointer, but in Scratch 3.0, the center button was removed. Costume centering had to be done by selecting and moving an entire costume, before an automatic centering feature was implemented on February 13th, 2020. In an announcement forum, ceebee states,
|... You can now align your artwork to the canvas center more precisely. You can do this by clicking your artwork and dragging it towards the center crosshair symbol. The paint editor will automatically align your artwork when your artwork gets close to the canvas center.
– ceebee, 
Because of the inconveniencies, not all users agreed with those updates and have suggested to bring back some features.
These four file types fall under one of three categories: uncompressed, lossy compressed (visual data is lost with compression), and lossless compressed (image is compressed, but no visual data changes). The first category includes BMP, which stores image data without any compression at all. JPEG files are examples of lossy compression, which may cause visible artifacts especially in simple images. Lossless compression makes a file look the same as its uncompressed counterpart but with a smaller filesize, and examples include PNG and GIF files (for 256-color images).