Resolution: The Wrong Spec

I was talking to a friend and industry colleague the other day who was a little frustrated with the way a recent project had gone.

The AV design included a large 1.9 mm dot pitch direct view LED screen in a large presentation space.  Based on viewing distances from the seated positions in the room, all the math checked out and the screen should look great in the space.

Then at zero hour, the client related that they wanted to be able to have people come up to the screen and collaborate. This meant that the dot pitch on the 1.9 mm solution was going to become very apparent. Realizing this, the client asked for the solution to be upgraded to 4K.

Hmmm.

For any of you that sell or manufacture direct view LED, you most likely already see the issue with the request. Changing a 1.9 mm solution to “4K” requires the screen to get wider and taller. Adding “resolution” to this solution just makes the screen BIGGER, it doesn’t actually add any detail.

What the client actually needed was more “pixel density.” The only way to accomplish this with direct view LED was to use tiles with a smaller dot pitch, which was cost-prohibitive based on the budget, or to go to an LCD based video wall, which introduced some bezel interruptions and changed the infrastructure and mounting needs.

The problem with the resolution spec is that it doesn’t actually relay “perceived” resolution.  

Question 1 – What looks better from 3 feet away: a 42″ 1080p LCD display or an 84″ UHD LCD display?

Most people would lean toward answering the UHD display given it is 2160p vs. 1080p, but the truth is the pixels are exactly the same size on both displays.

A 42″ 1080p display and an 84″ 2160p display have identical pixel densities, about 2751 pixels per inch (PPI). Many of you may have already known this or been able to conclude it rather quickly, so let me give you a harder one.

Question 2 – What looks better from 3 feet away: a 2×2 video wall made with 80″ 1080p LCD displays or a 160″ diagonal 1.2 mm direct view LED array?

This immediately becomes harder to figure out as we know the resolution spec alone tells us little about the perceived resolution, and the LED arrays are typically referred to by dot pitch, a spec not used in LCD displays at all.

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The answer is that an 80″ 1080p LCD display would look better from a perceived resolution perspective. It has a pixel density of 758 PPI, whereas a 1.2 mm direct view LED array has a pixel density of around 410 PPI. You’d need to upgrade to a .9 mm dot pitch direct view LED solution (735 PPI) in order to get the same perceived resolution.

To the credit of the direct view LED community, they seem to realize that “dot pitch” doesn’t readily convey resolution, and they do utilize “pixel density” as a specification on their data sheets. They include it in the form of “pixels per square meter,” allowing one to easily differentiate between different direct view LED solutions.

I would suggest that it may be time for LCD display manufacturers to start doing the same, and include pixel density as a specification. As I’ve illustrated, it can be ascertained from all the other data on the spec sheet but it takes a little math. Currently, an integrator or consultant would have to determine the area of an LCD display, divide the number of pixels in the display by the total area in square inches to get pixels per inch. Then they would have to multiply that by 1550 in order to get to the “pixels per square meter” specification included by the direct view LED crowd for a direct comparison.

Regardless of whether LCD display manufacturers include this or not, designers should be paying more attention to the pixel density of their solutions than the “resolution.” It can assist in determining whether or not direct view LED arrays will meet the clients expectations for perceived resolution, as well as determine whether that video wall should be a 3×3 constructed of 55″ 1080p dispays, or a 2×2 constructed of the 84″ UHD version.

Are you considering pixel density in your solutions? I’d love to hear your take in the comments below.

About Mark Coxon

Mark Coxon is an AV industry native and blogger for the rAVe BlogSquad. You can reach him directly at mark@marketexplosion.me.