Assumptions are dangerous in science
John2 wrote: ↑
15 Jun 2020, 13:55
So when you say that we need 1000Hz to get CRT clarity, I had always assumed you were by default talking about 1080p LCD displays, because I had always thought that you would need more than 1000Hz on a higher resolution LCD display to get CRT clarity.
CRT phosphor varies a lot in persistence. Short-persistence phosphor versus medium-persistence versus long-persistence.
CRTs actually had a bit of motion blur in the form of “ghosting”, if motionspeeds were fast enough, high resolution enough, and phosphor slow enough.
Now, imagine the most extreme possible situation: Radar CRTs are intentionally designed to be slow, in order to ghost (long persistence) their previous images, since Radar CRTs essentially operated at low refresh rates (e.g. less than 1 Hertz) to be in sync with a mechanically rotating antenna.
But a television tube doesn’t need to preserve a refresh cycle for that long, so phosphor is short. However, short persistence phosphor is often dimmer, so sometimes manufactured used medium-persistence CRT phosphor to make the picture brighter, at the cost of some extremely slight ghosting. Early color CRT tubes like the 1954 RCA first color TV were really slow (phosphor fade far slower than LCD pixel response today of a non-strobed LCDs), and improved over the years towards the 2000s.
Some models, such as GDM-W900 had a medium-persistence phosphor, and the default of 1ms is used for the CRT phosphor decay to fade 90%+. However, there are CRTs have phosphor decay that takes much quicker (territory of ~0.1ms).
Because of this inconsistency, 1ms was assigned the standardized CRT phosphor gold standard — anything that meets 1ms MPRT can be pretty legitimately called “CRT motion clarity”, regardless of resolution
, since CRTs can still motionblur (given sufficient resolution + motionspeeds).
Few people sat very close to large CRTs (e.g. 30 inch) running at high resolutions (e.g. 1080p). Most desktop monitors were 15 inch to 21 inch maximum, and TVs were viewed across a living room. So there was very little opportunity to witness the Vicious Cycle Effect as explained halfway down at www.blurbusters.com/1000hz-journey
But work around CRTs long enough, you’ll get familiar with the fact that some of them ghosted more than others. And if you looked closely at many old tubes, and compared to many strobed LCDs, it’s pretty clear that today, the venn diagram already overlaps in motion clarity capability, thanks to the modern emergence of Motion Blur Reduction
Some of them now can flash a strobe backlight for only ~0.25ms, with shorter strobe pulse length adjustments. And to match that, will require 4000fps at 4000Hz, mind you (1000/0.25 = 4000). So 1000Hz isn’t the final frontier (you are correct about that). That’s why I mentioned quintuple digit refresh rates near the end of www.blurbusters.com/1000hz-journey
in the wide-FOV retina-resolution situation (e.g. virtual reality).
Refresh rate limitations will equally show on CRT and LCD for similiar milliseconds number (Give or take, allowing error margin for differences in curve shapes) — it’s just CRTs never reached retina resolutions.
John2 wrote: ↑
15 Jun 2020, 13:55
Motion blur [in pixels of motion blur for same physical distance]
is not same between 1000Hz 1080p LCD and 1000Hz 8k LCD, the former will have noticeably worse motion blur to the human eye because of the higher resolution, so wouldn't the former need a higher refresh rate to achieve the same motion clarity of a CRT?
Fixed it for you.
No 8K 60Hz progressive-scan CRTs has ever existed, and electron beam spot sizes were never reliably tight enough for that, so it’s not possible to make an apples-vs-apples comparision.
The same effect also applies to CRTs too — higher resolutions would also have made phosphor limitations more visible, too. The phosphor illumination is darn near instantaneous (microseconds, just like a strobe backlight turning on too) but the phosphor fade takes a longer time to fade, typically hundreds of microseconds on most common CRTs.
Of a strobe-backlight-driven LCD panel (a way to reduce LCD motion blur without the need for insane refresh rates) — a strobe backlight pulse is more of a square wave (strobe backlight) and a CRT phosphor fade is more like a curved sawtooth (shark’s tooth) when seen on a photodiode oscilloscope. So the rise-fall asymmetry shows up to human eyes as asymmetric blur (e.g. leading edge or trailing edge artifacts — aka “ghosting”).
Remember, CRTs were often low resolution, so they were always perpetually motion-clear to most, but in reality, really high resolution material, on a sufficiently large tube viewed close distance, at really fast motionspeeds, could also blur/ghost on a CRT tube too. I’ve seen it happen.
Mind you, not nearly as badly as a ghostly radar scope — but enough to allow CRT clarity venn diagram to easily overlap with strobe-backlight LCDs of similar strobe pulse lengths.
In other words, it will nothappen with 256x224 Super Mario material, mind you — it’s always perpetually perfectly clear at the fastest Nintendo panning speeds. There was never retina-resolution-textures Super Mario brothers at 7680x4320 on a retina CRT — that never existed.
But if one did, the motionblur/ghosting would be visible subject to sufficiently high-resolution CRT with sufficiently high-resolution shadowmask or aperturegrille, with a sufficiently slow phosphor.
In reality, it only takes a medium-persistence phosphor on a sufficiently large tube (Widescreen 24” Sony W900 / FW900 tubes), with current videogame motionspeeds, to create an extremely slight amount of real-world motionblur on a CRT tube, such as testing TestUFO Panning Map
at about 3000 pixels/sec. That mapping ceases to be as clear as a stationary image, thanks to the CRT phosphor contributing to sufficient slowness to generate motionblur on a CRT tube surface that is slightly worse than a 0.25ms MPRT strobe backlight (reduced pulsewidth).
Then again, very few people have used sufficiently high-enough-resolution CRT tubes at sufficiently close viewing distances, to witness motionblur/ghosting caused by phosphor...
A simpler ghosting test for a CRT is bright objects on black backgrounds — there is a faint green ghost trail. In some slower tubes, that trail is about 10x worse. And in some early tubes with older phosphors, it was far worse than that (1000x+), like those early color CRTs such as the 1954 RCA Model CT-100 Color TV whose phosphors seemed to have in common with radarscopes than a standard monochrome TV.
As I’ve said in the first sentence of this post, assumptions are dangerous in science.
Many of Blur Busters’s writings on the main website, are intentionally simplified for a Popular Science audience rather than a Research Journal audience — since display advocacy is one of the prime goals of Blur Busters.
Blur Busters — our namesake.