spacediver
2[H]4U
- Joined
- Mar 14, 2013
- Messages
- 2,715
I was going through this thread and trying to make sense of a few things, so this post is to test whether my understanding is on the right track.
Let's make things simple.
Suppose we have an LCD panel. The number of shades, in a particular pixel, of any given color channel is determined by the following things:
1: How finely the voltage can be quantized (the voltage is applied to the molecules and cause them to shift/rotate, changing the amount of light that is let through).
2: How finely these molecules respond to voltage. If they're very volatile, then it's going to be hard to get them to reliably move by tiny amounts.
Suppose we can quantize our voltage very finely with arbitrary precision.
But suppose that our molecules are so volatile that they can only achieve 256 different orientations/positions between their most extreme positions.
This means that our panel is a very crappy 8 bit display. This is what its properties would be:
1: It would only allow 256 different shades of gray (to keep things simple, let's restrict our discussion to the neutral axis and not talk about individual RGB channels).
2: At any given backlight level, if you tried to remap the relationship between input video level, and applied voltage (i.e. if you altered the LUT of the panel), all you could achieve would be clipping/crushing.
This can be illustrated below:
If the molecules can only adopt these five particular orientations, then no matter what applied voltage we use for each position in the LUT, and no matter how precisely we specify that voltage, each of the five video input signals will be linked to only one of those five molecular orientations. So either we can display the full five shades of gray, or we end up with a quantization artifact and we end up with only four shades of gray, as shown below:
So, the only thing we can do with this panel is to raise the level of the backlight, which will just uniformly increase the luminance across all video input levels, or we can choose to crush input levels together. In the case of the above image, we have crushed levels 4 and 5.
So, given this model of how things work (and this is how I understand them to work - I could be well off on many parts), we're now in a position to have a meaningful discussion on what panel bit depth really means.
For the next part of the discussion, let's ignore spatial / temporal dithering, such as frame rate control (FRC).
It should be clear that any decent LCD panel is not as limited as the one described earlier. If a panel did indeed only have 256 possible molecular orientations, then any form of correction done to the luminance function of the display (e.g. gamma correction, white point adjustment, dynamic mode, cinema mode, etc.), whether implemented through the OSD or through the video card, would either result in no change whatsoever, or varying degrees of quantization artifacts.
If my thinking so far is correct, then this means that virtually all LCD panels are capable of more than 8 bit precision, in the sense that the molecules can reliably adopt more than 256 orientations/positions between their most extreme orientations/positions.
Suppose that, in fact, all LCD panels are capable of 1024 discrete molecular orientations, but that the circuitry of the panel is such that only 256 different voltages can be applied at any given frame/refresh.
In this case, one could greatly reduce quantization artifacts that are introduced by changes to the LUT, but we'd be limited to only 256 simultaneous shades of grey.
Have I got this right?
Let's make things simple.
Suppose we have an LCD panel. The number of shades, in a particular pixel, of any given color channel is determined by the following things:
1: How finely the voltage can be quantized (the voltage is applied to the molecules and cause them to shift/rotate, changing the amount of light that is let through).
2: How finely these molecules respond to voltage. If they're very volatile, then it's going to be hard to get them to reliably move by tiny amounts.
Suppose we can quantize our voltage very finely with arbitrary precision.
But suppose that our molecules are so volatile that they can only achieve 256 different orientations/positions between their most extreme positions.
This means that our panel is a very crappy 8 bit display. This is what its properties would be:
1: It would only allow 256 different shades of gray (to keep things simple, let's restrict our discussion to the neutral axis and not talk about individual RGB channels).
2: At any given backlight level, if you tried to remap the relationship between input video level, and applied voltage (i.e. if you altered the LUT of the panel), all you could achieve would be clipping/crushing.
This can be illustrated below:
If the molecules can only adopt these five particular orientations, then no matter what applied voltage we use for each position in the LUT, and no matter how precisely we specify that voltage, each of the five video input signals will be linked to only one of those five molecular orientations. So either we can display the full five shades of gray, or we end up with a quantization artifact and we end up with only four shades of gray, as shown below:
So, the only thing we can do with this panel is to raise the level of the backlight, which will just uniformly increase the luminance across all video input levels, or we can choose to crush input levels together. In the case of the above image, we have crushed levels 4 and 5.
So, given this model of how things work (and this is how I understand them to work - I could be well off on many parts), we're now in a position to have a meaningful discussion on what panel bit depth really means.
For the next part of the discussion, let's ignore spatial / temporal dithering, such as frame rate control (FRC).
It should be clear that any decent LCD panel is not as limited as the one described earlier. If a panel did indeed only have 256 possible molecular orientations, then any form of correction done to the luminance function of the display (e.g. gamma correction, white point adjustment, dynamic mode, cinema mode, etc.), whether implemented through the OSD or through the video card, would either result in no change whatsoever, or varying degrees of quantization artifacts.
If my thinking so far is correct, then this means that virtually all LCD panels are capable of more than 8 bit precision, in the sense that the molecules can reliably adopt more than 256 orientations/positions between their most extreme orientations/positions.
Suppose that, in fact, all LCD panels are capable of 1024 discrete molecular orientations, but that the circuitry of the panel is such that only 256 different voltages can be applied at any given frame/refresh.
In this case, one could greatly reduce quantization artifacts that are introduced by changes to the LUT, but we'd be limited to only 256 simultaneous shades of grey.
Have I got this right?
Last edited: