The DXF file format was created by Autodesk in 1982 and the intention was to create a format that was independent of CAD applications and therefore eased the difficulties of sharing files created by different applications. This was particularly important for early versions of CAD as reverse engineering of the closely guarded DWG format was limited. However in recent years the usefulness of DXF format has reduced due to DXF not being able to support more advanced CAD elements such as dynamic blocks. The market leading popularity of AutoCAD has also reduced the requirement for an application independent format.
DXF files are organised in way that allows the files to be opened by a normal text editor application.vA DXF file has a common format containing a number of sections. These include the Header which contains file property information, Classes, Tables, Entities, Blocks and Thumbnail Image section. The data contained within a DXF is known as tagged data which means that the tags identify how the data should be interpreted. For example there are a large number of group codes related to the creation of an ellipse. Various group codes allow for the definition of the start and end points, centre point and extrusion directions.
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PNG pronounced ping is a format for storing bitmapped (raster) images on computers. It was created originally to replace the GIF file format when it was announced that the companies who created the GIF format wanted royalties. PNG uses indexed colors and lossless compression (like a .GIF file), but without those copyright limitations; it cannot be animated like a GIF image.
PNG images are in many ways better than .GIF as they also include an 8-bit transparency channel, which allows the colors in the image to fade from opaque to transparent; GIF images only support fully opaque or fully transparent pixels. PNG supports palettes of 24-bit RGB colors, RGB images or greyscale or RGB images. PNG was intended to be able to transfer images on the Internet, not professional graphics, and so does not support other colour spaces (such as CMYK).
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