How many pixels/lines-per-Inch has your monitor or television?

By H.J. Muller

Old Format

The old format often referred to, as "4:3" is actually a dimensional math reduction for "12:9". The expression basically indicated that the measurement is four units wide there are three units in height or a portion thereof.

If a screen resolution is expressed as 1024:768 than this resolution expression is in relation to the width and the height of the screen. Thus, 1024 pixels/lines / 12 = 85 pixels/lines per inch of width. Consequently, the per/inch resolution for the height is 768 pixels/lines / 9 = 85 pixels/lines per inch as well.

The New Format
To calculate the new 16:9 format you can apply the same rule as above.
Example,
Recently I purchased a new format HD television set. It had the following printed specifications;

Width across corners, 37 inches. Resolution, 1920:1080 and I ask the sales person what the resolution per inch would be. He answered that term resolution/inch was not used and stated that the1920 pixel resolution was in reference to the size of the screen. His answer made me wonder because that would mean a shrinking and stretching matrix. Not possible! The fact that the pixel/inch information is not used nor specified, you can calculate it as follows,

Like in the old format, the basic horizontal/height (16 x 9) dimension unit is the basis for the calculation regardless how small or big the unit might be. Therefore,

Resolution / base width inches = resolution/inch so, 1920 / 16 = 120 or,

Resolution / base height inches = resolution/inch so, 1080 / 9 = 120 therefore, resolution is 120 pixels/lines per linear inch or 14,400 pixels per square inch. Or,

2,073,600 per 16 x 9 (144 sq inch) unit screen area. A 32 x 18 television set has 576 or four 16 x 9 screen units and a total of 8,294,400 pixels. That is a lot of LCD pixels.

Many HDTV units have a horizontal resolution of 1350 or less. Just divide the horizontal resolution by 16 and the vertical resolution by 9 to obtain the resolution per inch. For reference, Internet web resolution is 72 DPI so if you calculate resolution below 100 I would reconsider. Another resolution reference you can apply is the resolution of the human eye, which can distinguish equal contrasting separations between lines/dots/pixels up to 220 to 230 after it becomes one solid color/tone.

How large is your television?
Why television are measured by the hypotenuse of the screen is beyond me however, it could promotional related for that dimension will be larger than the actual or largest horizontal dimension of the screen.
The unit I purchased was promoted as a 37-inch screen and actual screen width and height were ambiguous so I got curious as to the actual geometry of the screen. I assumed that the manufacturer would like to stick to the 16-module dimension so I measured the height and the width and found it to be 18 and 32 inch confirming my thinking. Next I was able to calculate to actual selling dimension as follows: square root of (18sq. + 32sq.) = 36.715 inch. It shows you that sales literature related to televisions must be taken with a grain of salt.