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A pixel (abbreviated "px") is a single dot of light on any screen. Most computer screens have hundreds of thousands of pixels. A pixel is made up of three colors: red, blue, and green; when combined, they create the desired color that is displayed on the screen. Scratch 1.x uses pixel-based graphics, called bitmaps. Scratch 2.0 uses bitmaps and vector graphics; vector graphics are based on mathematically calculated splines instead of pixels.
Usage in Scratch
Steps, such as in move () steps, are measured in pixels in the ordinary size, 480x360px. In presentation mode, they are scaled based on the screen resolution. In small stage layout mode, a step is half of a pixel, so it takes 2 steps for the sprite to visually move a pixel.
The term "resolution" is common and refers to the number of pixels in an area by width by height. The more pixels a screen has, the higher the resolution is. The resolution of the stage is 480x360 pixels. The Scratch program can be displayed perfectly on all resolutions that are 1024x768 pixels and higher. If the resolution is lower (like on 640x480 or 800x600), some tools (particularly in the paint editor) may overlap one another. When working with Scratch on a low-resolution screen, it is sometimes helpful to change the stage to the small stage layout, which makes the stage 240x180 pixels, allowing more room for scripting and the paint and sound editor. However, this does make it quite hard to see the stage. A computer's resolution can go as low as 320x200 to as high as 9999x9999 (which is only possible with registry hacking).
For every resolution, there is a dimension to it. A dimension is a ratio of more than one measurement. In Scratch, the dimension of the stage is a 4:3 ratio, meaning that the width is 4/3 of the height and the height is 3/4 of the width. Since the stage has a dimension to it, no matter how large the size is, the aspect ratio stays the same, meaning that any resolution of the stage is always proportional to a 4:3 ratio.
Pixel density refers to how many pixels in a straight line there are per inch (abbreviated ppi) on a screen. Typically, larger monitors, like televisions, have low pixel densities because they have a larger display area, while smaller devices, such as smartphones, have high pixel densities. Higher pixel densities are needed for screens one views closely, and lower pixel densities are better for screens one views from further away.
Apple coined the term "Retina Display" for their high pixel density devices. The term is not used by other companies, but refers to the high resolution in a small area of many Apple products. The market for higher resolutions in smaller devices is increasing the pixel densities of many mobile devices.
In terms of the actual, physical pixels within a monitor, some can face issues that cause them to work improperly or not at all. Almost all pixels consist of a red, blue, and green light, which emit light to produce the proper color to the human eye. Sometimes one color in a pixel may go out, causing the pixel as a whole to appear a different color. Whole pixels themselves can die, resulting in a black dot on the screen. A pixel may also become "hot", or when too much light is constantly being emitted from the shell.