* When 'Pixel Lock' is on, the file's actual pixel dimension (in dark), remains unaltered, thus no detail is actuelly lost or gained. Only the size/resolution data (in light), which usually contained in a picture file's header, would be altered. Such data is relevant only for printing, or can be set by scanning, when "physical" paper dimension issues occur. Within the pure computer domain (e.g. web image, digital camera image), they don't mean much.

  Hint:  When scanning, turn 'Pixel Lock' off and try different detail amount (dpi) for a given paper size (inch/cm), to see what will be your file's pixel size.  When preparing backup or prints, turn it on to know what sizes (inch/cm) can be printed whith how much details (dpi), from a file of which pixel dimension is known..

  File weight (in bytes, Kb, Mb, etc.) depends on the amount of pixel. With unlayered, uncompressed formats (BMP, some TIFs, TGA, ...), those values are directly proportional

  Check out the static table to know which dpi values are suitable.

* The px (pixel) and Mpx (million of pixels) units are of different nature here: In Width and Height expressions, pixel (px) stands for a length unit. In the Size expression, a pixel is a surface unit of 1px² (it could correspond to one dot on an LCD matrix, for example), making the million of pixels (Mpx or megapixel) a surface unit of 1000px by 1000px.

  Only the knowing of the W/H Ratio makes it possible to deduce Width and Height in pixel from Size in megapixel. Only the Resolution in dpi, then, makes physical Width and Height (in cm or inch) retrievable.

* dpi stands for 'dot per inch', which, in most digital matrixes, is equivalent to 'pixel per inch'. It is always expressed regarding one dimension (a side, not the surface).

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