Converting between pt and pixels

Question

My netbook has a monitor with 10.1 inch length and 1024*600 solution. I think 1pt is about 1/72inch - is the following computation right?

Since the resolution is 1024*600, the diagonal has about 1186.83 pixels, thus 1 inch is about 1186.83/10.1 = 117.51 pixels, and thus 1pt is about 117.51/72 = 1.63 pixels, or 1 pixel is about 0.6127 pt.

Using this relationship, I've inserted an image into a LaTeX document, converting pixels to pt, and take the result as a parameter to includegraphics, but the figure in the resulting document is rather blurred.

1. Is the computation correct? if not, how or where am I wrong?
2. How can I insert an image into a LaTeX document with precisely the same dimensions as the original?

---

Updated:

I'm using pdflatex to compile the document and the image is a png file, and the reason why I do such a stupid computation is that with no width parameter set, the image shown in the document is larger than the actual size, and I can't work out why.

Answer 1

LaTeX is for creating paper documents. The units it uses refer to distance on the paper output, not on the screen. So if you ask for a distance of 72pts in LaTeX, you'll get 1 inch on your printout, but the distance you get on your screen depends on the zoom-level of your pdf or ps reader, which probably doesn't know how big your screen is.

If you simply want to get the raster grid of your image to fit to the screen grid, I'd say the best thing to do is get a higher-quality graphic if you can.

(PS there's a TeX stack exchange site where you could ask your question too...)

Answer 2

I don't know if it will make any difference, but TeX actually uses 72.27 points to the inch (as it predates PostScript, which set the standard 72 points to the inch).