@Rhia474: Indeed thats a bit misleding cause there are only named the DPI and pixel dimensions. That's only the half of the story. The first image is having width of 1069 pixel / 300 DPI = 3.563333 inch and the second image has 1343 / 72 = 18.65277 inch. These dialogs are from Microsoft given properties dialog, i'm right ? Ok, MS is not God ( maybe even some floors deeper ;-) ) so what is missing is the size of the paper this shall be printed. So how good the resolution will come out is undefined. As far as I remember (not at my Poser PC) the size dimension can be given in pixels or in inch, cm or such real values. Would be interesting if you load both into for example Photoshop what that will say to the dimensions.

There is at least one format, BMP - very old and lossless like TGA, there I have often worked with the pixel cause they get saved line by line straight behind into the file. And therefor it's rather simply to calculate the length of a diagonal line through saved image by using the Pythagoras formula a² + b² = c². c is the searched diagonal length and with a and b its easy to determine the y,x-coordinates of the given start and end points cause they parallel with the x and y axis. We have used that to determine the precission of tools in rubber industries. Works only with lossless saved images cause the pixel count in compressed files like jpeg is variable.

By the way to keep it not to easy also the Bit depth is having impact in declaring how colorful the image will be. 24 is meaning that 3 Bytes are used, 1 Byte = 8 Bit = 256 (correct 255 cause counting from 0). So 24 Bit is RGB, one Byte for one color-range either red, green or blue and is normally called true color. For example GIF is normally often 8 bit and so not true color. Also black-white images normally only need 2 Bit and are tiny. For my example with BMP above it's essential cause one Pixels is representated by 3 direcly following bytes. In the great times of GIF BMP and TGA and TIF were most important cause able to save true color. JPG came later to reduce the immense size of the files. In times of harddisks below 1 GB and floppy disks essential but with the price of reduction losses.

Oh, where are the times if I now look to my terabytes of hardisks ... but no chance one has stayed - MS Windows will fill them with tons of shit nobody is finding and needing ... :-o