So a clear pixel (the W in RGBW) would preserve the original brightness of the backlight more so than the RGB subpixels, which then compensates the brightness loss of the PenTile matrix. In other words, the whites aren't adding to the brightness, they are helping reduce the brightness-subtractive nature of the rest of the subpixels.
While I find that a creative solution to the brightness problem, the image clarity problem still exists. Here's what PenTile RGBW looks like:
Each pixel is made up of 2 subpixels. According to this image, a standalone pixel can either be light blue (combo of blue + white) and yellow (combo of red + green). That's not so great for colors like cyan and magenta (no relationship of red+blue or blue+green in a given pixel. Whereas in traditional RGB square/stripe, all 3 primary colors are present in a single pixel, so each pixel can represent ANY color.
Therein lies the disadvantage of PenTile RGBW. For certain shades, you need more than 1 pixel to represent a given color, and that is a loss in resolving power (resolution in the classic sense).
Furthermore, RGBW shares a disadvantage with RGBG in that subpixels of the same hue are now farther apart from each other. That means that the screen door effect for large areas of solid colors (common on web sites and app UI elements) will be amplified.
I am glad that folks are discussing PenTile technology in depth. Full Disclosure Statement: I am the CEO of Nouvoyance, the developer of PenTile Technology.
But please allow me to correct a couple points from above. First, while incorporating the W (white, actually clear, filterless) subpixel is part of the improved energy efficiency gain over RGB Stripe LCDs, the reduction of the number of subpixels from a fixed three per pixel, to only two per pixel (on average) is also part of the improvement, a very significant part. This is because the amount of wasted space from the regions between subpixels is reduced. Between subpixels their is a "black matrix" that blocks light. It is important to block the light in the borders because otherwise it would leak light when trying to make dark colors and black. The width of these boarder areas is fixed; Thus, as the subpixel density (resolution before subpixel rendering) goes up, the aperture ratio, the ratio of light transmitting area to the light blocking area, decreases rapidly towards zero. In high resolution panels, this loss of aperture ratio is very high, thus reducing the subpixel density, as PenTile does, greatly improves the aperture ratio. Thus, the W subpixel is not trying to compensate "the brightness loss of the PenTile matrix", is is adding to an already improved transmissivity of the panel. The combination of the two effects, at the resolution of todays smart phone panels, is to approximately double the light transmissivity of the panel.
With increased light transmissivity, one can choose to lower the power of the backlight for the same brightness as seen by the viewer, or increase the brightness for the same power.
For OLEDs, the same issue of black boarder to emissive area occurs. But in this case, it is known as "Fill factor". PenTile RGBG reduces the wasted area to the black boarder, increasing the fill factor. This means that the panel, for a given absolute max brightness of OLED material, can be brighter. It also means that for a given fixed brightness, the current density, the amount of power per illuminated OLED material, decreases. This reduction in current density increases the lifetime of the material (the amount of time in use before it begins to fade and change color) making a high resolution OLED panel practical for real products.
The second point I wish to clarify is that for PenTile panels, a pixel is NOT represented by just two subpixels. Instead, incoming pixel data is first converted from RGB to RGBW, then subpixel rendered, mapped, using varying levels of intensity, such that the impression on the Human Vision System is nearly the same as for the RGB system. If in a given image, we were to change the value (color and or brightness) of a single pixel, from one to up to ten subpixels values on the PenTile panel may be changed, depending on the the color of both the changed pixel and its surrounding pixels. The human eye always compares and blends colors between "pixels", over a certain area, depending on the colors. Thus, luminance resolution is maintained...
...but the commenter I quoted here is correct, the color, but not the lumimance, resolution is reduced, but only in the diagonal direction, and only by a small amount. But this is OK, since the human eye has much lower resolution in pure color than in luminance. The limit of resolving power for the human vision system (HVS) is 30-60 cycles per degree in luminance, 6-8 cycles per degree in the red/green color axis, and 3-4 cycles per degree in the yellow/blue color axis. Today's smart phones are presenting information at about 25-30 cycles per degree. So, reducing the color resolution by a small amount is "OK".
The final comment is absolutely true, the distance between the same color subpixel is increased, compared to an RGB Stripe panel, and "pattern visibility", called the "screen-door" effect here, may occur for solid colors. This is one reason why PenTile technology is only recommended for higher resolutions. As displays continue to be spec'ed at yet higher resolutions, this effect will become less of an issue.
Im just giving you a hard time.
