As I mentioned earlier, I spent a lot of time this afternoon taking readings and adjusting the LUT (currently, that means editing a text file, uploading it to the box, waiting for it to change and measuring) at 0-15% in 1% steps, and 15-100% in 5% steps, with a total of 33-points. I've now put that into a spreadsheet to have it fill in the gaps to create a full LUT and uploaded it to the VideoEQ.
Note: It looks like I made the same mistake right next to 0 as I did the first time (having the last couple of points drop to 0 sharply rather than simply being cut off) so I'll have to correct that.
It also looks like there's some unevenness with the LUT in those 1% steps that might
look better if they were simply removed/averagedI'll have to try it and see.
I'm actually wondering if, because it's a CRT, I should just use two pointsone at white and one as close to black as I can accurately measure, as it seems like the LUT is mostly a straight line. (the non-linearities may simply be errors in the measurements) Something to experiment with anyway
As it is though, it is a significant improvement over the LUTs created from measuring in 10% steps. (really needed more data near black to get it right)
I should point out that my setup is a worst-case scenario: 8-bit in (so 8-bit out) and I'm using a CRT which does not posterise the image like a flat-panel/projector would, so any
loss in precision is visible whereas a flat panel may mask some of it with its own imprecision.
With this new LUT (which I am sure can be improved further) I would say that posterisation is not an issue 90% of the time. 9% of that last 10 is visible but not problematic, and 1% of the time ugly
posterisation is noticeable.
What I mean by ugly' posterisation is when you have very obvious discolouration, rather than simply banding in the image. Banding is unwanted but tolerable to some degree, whereas discolouration is not. An example of ugly posterisation is the red/yellow blotches in this image
. (of course nothing looks that bad)
I have tested a number of films/scenes that I remember being problematic on many of the digital displays I have used, and I can confidently say that while there is posterisation introduced into the image, it is much less noticeable, but more importantly, there is a lot less ugly' posterisation than on any of them.
There are two things I need to mention though that may be affecting this:
- My player is dithering which will be helping to mask the posterisation. (HTPC using madVR)
- These comments are all relating to Blu-ray. (which is 99% of what I watch these days) With DVD, posterisation is more noticeable as a result of the lower resolution and higher compression. It's still generally showing as banding rather than bad discolouration, however.
So, is it worth it? Probably
, if you are willing accept that there may be some posterisation introduced into the image, and can spend the time to get a LUT properly adjusted. This should be a lot easier once AV Foundry release a GUI tool, and if the CalMAN v4 automation works well. (at the very least I expect it will do 90% of the work)
Aside from the fact that it is introducing posterisation into the image (again, may not be noticeable/problematic depending on your display/setup/LUT) I would say that it is a significant upgrade in my systemand I haven't made use of the CMS at all yet. (though my display is fairly accurate already)
Having the greyscale & gamma as close to being linear as possible makes a massive difference to the image. Most displays do not even have the controls necessary to get gamma flat, let alone getting it flat at the correct level. (2.35±0.15)
With my CRT this has allowed me to hit 2.35 down to the lower limits of my meter, and keep black at zero luminance.
The most noticeable effects of this on image quality are:
- Contrast is up significantly. Previously to get anything close to a flat greyscale/gamma I had to raise the brightness, reducing most of the black-level advantage CRT has. It also had to be ≈2.22 to be flat, rather than 2.35 so combined with the raised black level, the image looked washed-out.
- There is a lot more pop' in dark scenes. There are some scenes in films that, no matter what I did, always looked dim/flat/murky/drained of all colour. With the controls on the CRT, you could either raise the black level to make the detail more visible, or lower it to have them looking appropriately dark at the expense of it. Neither situation was ideal, and shadow detail was never well definedit all seemed to blend together.
With the LUT, these scenes now look the way they always should have done. Even though they are dark, shadow detail is clearly visible (but not because it's been exaggerated the way some displays do) there is a lot more colour in the scene. The image just pops' in a way I've never seen before. I can't think of any way to better describe it.
This may just be a CRT thing though, as the black level on most flat panels is too high to run a flat 2.35 gamma.
Compared to other devices/software I have used, this produces much better results. Anything that has simply offered options to raise/lower gamma has washed out the image near black, and compressed highlights.
Anything offering finer control has either introduced a lot more posterisation or simply hasn't had enough control for the loss in precision to be worth it. (it's also cost a lot more)
For the money, the VideoEQ seems like it's a great device. As good as the results are now though, it really makes me wish that it could output 10-bit regardless of input bit-depth, and really, the more precision the better. Maybe version 2. (hopefully this will sell enough to make that possible)