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My first article where I tried to measure the response time characteristic of several 15” LCD displays (see our article called Closer Look at 15” LCD Monitors Features: Pixel Response Time) received very big feedback from the readers. Some of them asked specific questions and shared some suggestions about the applied measurement methodology. So, I will first try to answer most frequently asked questions.

First of all, some readers expressed a supposition that different colors on the screen may switch not simultaneously because of certain peculiarities of the display electronics (although physically all sub-pixels are absolutely identical in this respect). Furthermore, odd and even pixels may also switch not simultaneously. So, as I measure the rise time for an entire (white-colored!) line, the measured response time would be overestimated from the start. I took these considerations into account and performed the measurements on both: white and red lines and on a dotted line of red pixels (next nearest). But I discovered that the result shown by each of the displays reviewed today was the same whatever the color or the shape of the line was. As the signal-to-noise ratio is the highest for the measurements taken on a white line, all oscillograms shown in this article are taken for this particular line.

Some readers also criticized me for assuming that the manufacturer specifies response time according to the ISO 13406-2 standard. Let me make my position clear once again. If the manufacturer doesn’t explicitly tell how exactly he measures response time, I think I have the right to assume that he sticks to the industry standard. Sometimes the measured and specified response times differ greatly, which can mean that the manufacturer either tells wrong numbers or measures this characteristic according to his own methodology. But tell me, do these two variants differ for a common user like me? In both cases I am misled because I will compare this response time value with the values of those displays that honestly tell their response time according to the standard.

I was also asked to mention my own subjective impressions about the response time so that you know how the numbers reflect visually the image quality. Still, I chose not to do that because my eye perception might depend on a number of factors and couldn’t be measured or calibrated. To compare visually two displays, close to each other in characteristics, I would have to place them side by side and meditate for a while, viewing one after another… And then I would have to do the same for all displays… So, once again, I won’t allow my subjective opinions to mess up with the objective data. Of course, I will say a few words about the visual perception of response time for some particular displays. For example, Samsung 172B has high total response time, but produces a very slight image blurring thanks to its low pixel rise time.

 
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