When graphic designers talk about bitmaps, they mean either the BMP file format or simply a raster image in any format. Any digital image with dimensions given in units of pixels is a raster image. You create them by taking pictures with a camera, capturing a desktop screenshot or saving a file in an image-editing program. Most image editors have an option to save files in BMP format, a lossless compression format similar to TIFF and appropriate for high-detail, offline work.
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Make Bitmaps in an Image Editor
In Windows 8.1, use Microsoft Paint, Paint.net or Gimp to make a new raster image from a blank file. Each of these programs has tools for drawing patterns or text on a canvas and supports saving your file in BMP format. Alternatively, open an image from your computer in one of these editors and save it as a BMP file. This choice is appropriate when you need to open an uncompressed image from a camera, usually in RAW format, in a program that doesn't support RAW files. For most graphic design purposes, a bitmap doesn't need to be in BMP format, and in many common situations, it's a bad choice. For example, BMP files as texture bitmaps are excessively large and take up more memory than necessary. Saving a bitmap in JPEG format reduces its file size without losing any perceptible quality, making it a good choice for textures and online images.