Is it your position that a test pattern with a block of 10 blue pixels at 100% and everything else black will provide the same luminous intensity as a test pattern of 1 blue pixel at 100% and everything else as black?

Do you disagree that the units for luminous intensity are lumens per steradian angle?

If a shutter was put over 100% of a subpixel instead of 90%, what would happen to the luminous intensity of that subpixel with shutter?

--Darin

This is where all of us are talking past each other. The emissive area (including the area around it)absolutely has everything to do with how bright that subpixel appears. It's the net effect that matters, for that area.

It feels like one more person has gotten confused by the word intensity as if it is the intensity of the light within the pixel when we are talking about the photons that reach far from the pixel.

Or maybe going by something that said if the current doesn't change with OLED then neither does the intensity.

I purposely used a shutter in my example instead of something like making the subpixel smaller since I didn't want to change anything like resistance. With a shutter it shouldn't matter what the underlying technology is. A person shouldn't have to know whether it is OLED, LCD, or even a DLP chip, where the example could be what happens if 90% of each pixel was painted with perfect black paint.

I'm fine with being proven wrong if somebody can do it, but one thing that seems off to me is the argument that luminous flux goes down, but luminous intensity doesn't. The reason I find this strange is that luminous intensity is just the luminous flux for 1 steradian angle and if the angles of emission don't change those values move together.

With a point source emitting in all directions we have the following equation:

Luminous intensity = luminous flux / 4*pi

If the emitter is emitting uniformily in a half circle then we have the following equation:

Luminous intensity = luminous flux / 2*pi

So, if we haven't changed the angle the light is emitted, how can the luminous intensity stay constant while the luminous flux goes down?

--Darin

Sure, but I still contend that we're slipping away from the bottom line here.

Hold on now. "Current" or "Current Density" ? Both have been used in this conversation so far.

Yes.

No, I don't disagree.

In that case you have no source of light, so you have zero luminous intensity and zero luminous flux. In order to have some luminous intensity, you need a source of light, no matter how big it is. The smaller the light emitting object is, the bigger the difference between its luminous intensity and luminous flux, because the flux is directly depending of the size of the emissive object.

And since the eye (brain perception) deals only with luminous flux, if the blue OLED subpixel of Samsung 55S9 is twice as big compared to red and green one, then it has to be driven with 2 times less current and it will have the same luminous flux, but will last longer.

The eye sees luminance. It is not concerned with luminous flux.

I think everyone here is not understanding the role the eye plays. I tried explaining it in my last post.

When the light source is an effective point source (which a pixel is) our eye will perceive intensity changes with area. If the source is extended (has a perceivable area) then we will see a constant luminance as area changes.

All the examples here must specify a point source vs an extended source.

So, how did the lumens per steradian not go down when blocking 90% of the tiny subpixels that a human can't see any size for?
Not sure where that can from. Take a candle and put it a ways away. Now focus the beam down to a small angle (like a flashlight). The luminous flux will stay the same (assuming 100% efficiency for the moment), while the luminous intensity for the direction it is pointed will go up. Is it your position that a human wouldn't see a difference because it was only luminous intensity that changed? If not, why would a human notice a difference with a flashlight pointed at them from a far distance between the flashlight focused as normal and taking the focusing lens off so the light source is in the open like a candle?

Maybe we are using different definitions of luminous intensity. Do you disagree with this definition from Wikipedia?

"In photometry, luminous intensity is a measure of the wavelength-weighted power emitted by a light source in a particular direction per unit solid angle, based on the luminosity function, a standardized model of the sensitivity of the human eye."

If it is easier we could consider radiant flux and radiant intensity since they have a similar relationship as luminous flux and luminous intensity, but don't require scaling for the eye's perception.

Here is Wikipedia's definition for radiant intensity.

"In radiometry, radiant intensity is the radiant flux emitted, reflected, transmitted or received, per unit solid angle"

Do you disagree that the radiant intensity goes down when shutters cut off 90% of each subpixel?

--Darin

In most of my examples we know that the sources are extended (have size), but that we are viewing from distances where they are perceived as point sources.

I know you know this, but they don't have to actually be point sources, they just have to be perceived that way. Like my moon and star example. We know the stars are physically bigger sources of light, but are perceived as point sources because of our distance from them.

Subpixels don't have to actually be point sources to be perceived that way. So, we can treat them as extended sources when discussing certain aspects (like blocking 90% of their area) and as point sources when discussing other aspects (like how a human from a distance perceives them).

--Darin

No you can't treat them as extended sources unless you are close enough that the subpixel area is resolvable to your eye.

Extended source = If you block 90% of the area the luminance and intensity remain constant to the eye

Point source = If you block 90% of the area the intensity drops

When viewing the screen, the eye treats the screen as a non-uniform extended source wherein the luminance of all the point sources (subpixels and black space) are averaged.

So the perceived brightness of the display will not change with a bigger blue subpixel at lower current density.

A true point source doesn't have area, so you can't block 90% of the area. You have to get close enough so that the item can be treated as an extended source in order to block 90% of the area of it, then move back to where it is perceived as a point source even though it has area.

If you disagree, are the blue subpixels point sources if viewed from up close with a strong magnifying glass? If not, do they actually become point sources when viewed from a distance, or just perceptual point sources?

The engineers working on modifying subpixel sizes cannot view them only as point sources.

If your job was to block 90% of the area of a point source, how would you do that?

By your definitions, if I view a TV from 2 miles away while somebody else views it from 10' away. is the TV an extended source or a point source?
Using the EF9500 as an example, if shutters were put in that could block 90% of the area of each blue subpixel, would the perceived brightness to a viewer at a normal viewing ratio change between having the shutters opened versus closed?

--Darin

I wasn't meaning it to be that specific. Just speculating on how somebody might have gotten to a conclusive that luminous intensity couldn't change just by blocking part of a light source even though the luminous flux changed. Using a shutter doesn't change current or current density in a subpixel, so neither matter for that example.

--Darin

The reason I asked those questions is that I can see pixels on my pentile OLED Tab S2 almost all of the time (that's it, I can see pixels on pure colors such as red, green and blue, can't see them on white, though) and if I move far enough away not to see them the perceived brightness appears to remain the same... whether I can see them or not does not seem to have any bearing on the perceived brightness of the display... I mean, remember all those people complaining that they could see pixels on pentile OLED displays and none of them, to the best of my knowledge, ever observed a decrease in brightness between when they could see the pixels and when they couldn't.... Just food for thought, you know...

Attached Thumbnails

 

Could you put up a single green or blue pixel on black, then block part of that pixel with something and see if your perception of how bright that pixel is from a distance where you can't see individual pixels changes between blocking part of the pixel and not? Then do the same from up close with a magnifying glass or strong reading glasses.

Thanks,
Darin

I do have neither a magnifying glass nor strong reading glasses on me right now, but from what I can see the farther away I get from the blue pixel (or a small collection of the blue pixels if I zoom in) the dimmer it gets. If I block a small collection of blue pixels, it (the small collection of blue pixels) does not appear dimmer unless I put some distance between me and it.

P.S. I would really appreciate it if some other people here could try and perform the same experiment (with their OLED devises) so that we could expand our database and see if others see the same things I see.

Just tried the same thing with the Samsung Tab S 10.5 with an RGB stripe OLED display. The results are as follows:

If I try and cover a portion of a blue pixel (or at least what I think the blue pixel is) it does not make it appear any dimmer unless I put some distance between me and it.

If I put up a small collection of blue pixels and cover some of it it (the small collection of blue pixels) does not appear dimmer unless I put some distance between me and it.

Also, if I move far enough away from the pixel it seems to disappear completely.

Attached Thumbnails

 

It sounds like if you cover part of the pixel (or group of pixels) it disappears at a closer distance than if you don't cover part of it. Is that right?

I would say that is because the partially covered pixel appears dimmer when you are far enough away for it to be perceived as a point source.

You could also try changing the video level of the pixel. For instance, if you change it from 100% video level to say 50% video level without covering it in either case it should disappear closer to the screen in the 50% case for much the same reason that a partially covered pixel would.

Depending on gamma, going to 50% video level for a whole block of pixels should appear about as bright as if you blocked 80% of the pixels or just made it easier and illuminated only 1/5th as many pixels, as long as you are far enough away to perceive a single point source.

For example, you could compare a pattern with 10 blue pixels at 50% video level (~20% luminance) to 2 pixels illuminated at 100% video level, from a distance.

Or to keep the physical size about the same you could compare a block of say 100 pixels at 50% video level with the same size block at 100% video level, but with 80% of the pixels off and spaced somewhat randomly within the 10x10 area.

--Darin

This is far from perfect, but here is an image that contains a block of video 235 blue, then a block of video 126 blue, then a block of video 235 blue with much of the area blocked.

People can zoom up and see what it looks like when your vision can see the area clearly, then zoom down and/or move away from the screen to see how bright each one looks as the blocks get closer to looking like point sources.

If anybody thinks the rightmost block doesn't have lower average luminous intensity and lower luminous intensity as the leftmost block when viewed from a distance where it is a perceptual point source or close to it we should talk about what the definition of luminous intensity is.

Hopefully this picture will also help to explain how if you block part of a subpixel you would have to make the leftover part of the subpixel brighter than that part was before in order for the whole subpixel to look as bright from a distance.

--Darin

Attached Thumbnails

 

A true point source does not exist. Like I said, at a certain distance or area, your eye begins to treat an extended source as a point source. Luminance becomes intensity as only one angle exists.

If you can visually resolve the area, the source is observed as extended. In that case your eye can sense luminance which is independant of distance or area.

2 miles away is a point source, 10' away is an array of point sources we average into an extended source. The perception of luminance is dependent on the uniformity of the source. This holds true with luminance meters or your eye. In a display the source is inherently not uniform due to the pixel pitch.

Absolutely. The average luminance of the array of point sources had dropped. So the extended source (average of the luminance of all point sources) luminance had dropped.

This is the crux of this discussion. The fixed area of the display is an array of point sources. Covering the individual pixels by 90% is not the same as covering the screen by 90%. The reason is point source vs extended source and how the eye will average luminance over an extended source.

This is a great study as well. If you watch a single white pixel on a black screen and move further away the pixel will absolutely start to look dimmer (less bright) as it is acting like a point source (like stars moving further away). However, if the entire screen is white you won't observe any change in luminance (brightness).

Why? Because we perceive the entire screen as an extended source as our eyes average many multiple point sources that make it up. As we move backwards the distance from the screen and the area of the screen change proportionaly and we see no change in average luminance.

Yep. We can treat things as a point source, but we can't block 90% of the area while doing so. We have to get close enough to be able to adjust the area and at that point we are treating them as an extended source in order to be able to block the area.

You said I was wrong about:
What is it you disagree with? If you still disagree, how would you block 90% of a point source without treating it as an extended source while determining the area to block?
Sounds like if I ask you whether a blue subpixel is an extended source or a point source you can't say since you don't have enough information. Maybe just a semantic thing where I would say in the real world the subpixel has area, but it cannot always be perceived. It is sometimes expedient to treat it as having area and sometimes not. It seems like we basically agree other than maybe some semantics like I think it would be difficult for an engineering team to design televisions if they could only treat subpixels as point sources. Like a lot of things in science and engineering we can consider the same thing in different ways depending on the goal.

The fixed area of the display cannot be treated as just point sources by the person who is supposed to decide things based on area of the individual subpixels and pixel areas. For things where area is not needed they can treat them as point sources.

--Darin

Of course you can. Take an extended source, cover 90% of it up, then move far enough away until it is observed as a point source and see how it looks. I'm a little confused at this statement.

I meant you can't treat a subpixel as an extended source unless you are so close to it to observe a resolvalbe area.

Seems like semantics here. I was just saying you can't make conclusions about the extended area properties and the point source area properties in the same example as they are totally different.

It is simple. If I'm close enough to not see a change in average luminance, the subpixel is an extended source I can resolve. If I do see a drop in luminance the subpixel is a point source.

I'm confused by your claim since you just did what I described and you said I was wrong about. You treated the same object as an extended source in order to block it and then as a point source after you moved back. Didn't I say we could view it as an extended source to block the area and then as a point source to consider how a human from a distance perceives it?

Seems like you agree with me that you can't really block 90% of the area while just considering it as a point source.
True, but you can be up close treating something as an extended source while you block some area of it while having an observer at a distance who views it as a point source. Like if you covered part of the light from a lighthouse while asking somebody on a distant ship what they perceive.
Didn't you just do that above with treating the pixel as an extended source and then moving until it is perceived as a point source? Like I mentioned, it doesn't have to even be the same person. We can consider the properties of a single example when it is perceived as an extended source and when it is perceived as a point source. Could be 2 people at the same time. Of course the perceived properties are different, but we can consider both.
And if 2 people each observe one of those at the same time it is both. Simple, right?

--Darin

Just confusion. I read that you were making conclusions about the subpixel as an extended source and applying that towards what the average viewer sees.

I don't agree. I think we tackle problems differently. I'm not working in considerations. In all examples I am working in perception. In other words what will the source look like up close or from a far.

This tells me we are on the same page. That makes sense.



Not quite. It is interesting to me at what point the human eye (as an array of luminance sensors) resolves to one sensor unit. Maybe that is the threshold of a point source showing a change in perceived brightness.

I'm not sure I understand why not. It will when you take into account the area around it. This is, after all, how half-tones work.

In a printing system (a subtractive process), each of the 3 colors (leave out black---it's an oddity) are always the same ink and never change. Yet the size of the dot is what yields the perceived brightness for each of them. I have written this routine many times. It's no mere dithering.



Or more simply (pay attention to the left third of the image):

The statement was referring to the larger blue subpixel with lower current density (not the 90% example). Viewing up close the subpixel will look dimmer. From a far the display will not look any dimmer.

The 90% cover up example will be the exact opposite.

I can see why it was not clear. I'll edit that post.

Gotcha.

I have just finished conducting the block experiment. Here are the main observations (plus photos):

1. The leftmost block of pixels, at all distances, appears brighter than the center and the rightmost blocks. At a considerable distance, the center and the rightmost blocks appear roughly the same, as far as the brightness is concerned.

2. The leftmost block disappears the last, whereas the center and the rightmost blocks seem to disappear at roughly the same distance. They also (the center and the rightmost blocks) seem to disappear at a lesser distance than the leftmost block.

3. If I get close enough to the screen so that my eyes can resolve the constituent "parts" of the rightmost block, those constituent "parts" appear brighter than the center block, but I would not say that they appear as bright as the leftmost block.

Well, that's about it.

Attached Thumbnails

         

         

       

Thanks Stas. Here are a couple more versions where I made the blocks bigger, put the solid block with low video level on the right, and for one of them put no gap between the blocks.


If people who are interested open them in Microsoft Paint they can use the eyedropper and then "Edit colors" to verify how each part is encoded (or to change the encodings), and also zoom the images either way for inspection.


BTW: I don't know what percentage of the area of the center block this time is black and what percentage is blue. I was just winging it.


--Darin

Attached Thumbnails

   

From the example I just posted it seems like there is a gradual drop-off in the ability to perceive area change versus just a brightness change when part of the area of a light source is blocked. It makes sense to me that our ability to sense the area decreases as we get closer to viewing the object as a point source.


--Darin

Given the well known issues LG's OLEDs have with shadow detail and vignetting etc at just above black level (eg. https://www.avsforum.com/forum/40-ole...600-oleds.html) the following video is of interest.

https://www.avsforum.com/forum/138-av...-ultra-hd.html

At the very end Joe Kane talks about OLED's and how 2.4 gamma levels are CRT based and not really suitable for OLED's and LCD's. He suggests we should change to a 1.0 gamma level.
This may help explain the issues that LG are having with their OLED sets at just above black level.

LG expected to finalize 8G OLED investment plans in November, says report

Source (Digitimes): http://www.digitimes.com/news/a20151104PD204.html