Image metadata is stored in a human-readable ASCII header. The information in this header is designed to calculate the byte offset of some information in the subsequent data unit to support direct access to the data cells. Each FITS file consists of one or more headers containing ASCII card images[a] that carry keyword/value pairs, interleaved between data blocks. The keyword/value pairs provide information such as size, origin, coordinates, binary data format, free-form comments, history of the data, and anything else the creator desires: while many keywords are reserved for FITS use, the standard allows arbitrary use of the rest of the name-space.
FITS image headers can contain information about one or more scientific coordinate systems that are overlaid on the image itself. Images contain an implicit Cartesian coordinate system that describes the location of each pixel in the image, but scientific uses usually require working in 'world' coordinates, for example the celestial coordinate system. As FITS has been generalized from its original form, the world coordinate system (WCS) specifications have become more and more sophisticated: early FITS images allowed a simple scaling factor to represent the size of the pixels; but recent versions of the standard permit multiple nonlinear coordinate systems, representing arbitrary distortions of the image. The WCS standard includes many different spherical projections, including, for example, the HEALPix spherical projection widely used in observing the cosmic microwave background radiation.[5]
You need to get the size right. dpi is a measure for resolution and thus is also related to the file size in terms of bytes. I edited the logo (image) in Impress and xnview. Print-out quality is good. I did not try but possibly I could even reduce the image quality (pixels / inch even more.
XnView 2.0 is available in different versions. You can download a minimal, standard or extended version from the developer website which are all free and available as portable versions or setup files. The versions differ in regards to the plugins and addons that they ship with. The minimal version ships without any, while both the standard and extended version ship with additional plugins and extras.
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