While you are correct, there is another aspect to power in displays:
The most important component of LCD power is the back light that illuminates the display from behind. The overall transmission of LCD is only about 5% or so, which means that the back light behind is as much as twenty times brighter than what the user sees.
Increasing the pixel density implies that the pixels are smaller. Which means that the circuitry takes a larger fraction of the pixel [1]. Which means that more of the light is blocked. Which means that the back light now needs to be still brighter to compensate. As a result, iPad 3 back light uses 2.5 times more power than iPad 2 back light [2].
I am interested in knowing more about the logic and interface power in the way you have described. Please let me know if it is possible to get in touch.
[1] http://www.extremetech.com/computing/122725-what-the-ipad-3s...
Interesting! Thank you for sharing!
Prompted by an offline discussion I thought it'd be a good idea to talk about the other effects. I focused my post around the power requirements of the image processor circuitry. However, there are two additional components to an LCD display system: Display logic and Backlight power.
Display logic is, as the name implies, all of the circuitry required to drive the pixels. This is everything from the data connector on the raw LCD panel up to and including the TFT transistors on the glass itself and the transparent interconnects (also on the glass). The on-glass circuitry has complex parasitics and capacitive loading that also causes a fluctuation of drive current based on the randomness of the images.
Here's sample data from a 24 inch 1920 x 1200 LCD:
As you can see, a pattern with maximal excursions in the data causes the display logic current (and therefore, power) to nearly double.In very (very!) rough terms this current is also a function of display resolution: Twice as many pixels will demand double the current. Going back to the iPad 2 vs 3 example, the the new iPad has exactly four times the pixels of the iPad 2 display, therefore, it should require four times more display logic current than the older model under all uses cases.
The backlight may or may not demand more current as display resolution increases. Comparisons of displays of equal physical size but vastly different resolutions do not reveal a this effect to be an absolute rule. A lot depends on the design of the panel and the internal optics.