leDahu and all - what an incredible tool
this spreadsheet is! I cannot thank you enough for the time you have spent creating this, translating it, and sharing it with all of us.
Normally I put off calibrating the gamma because it is such a long and frustrating ordeal. But motivated by your spreadsheet I decided to try it out last night and the results were nothing short of fantastic.
To start, let me say that I was able to accomplish an ideal custom gamma curve in 15 minutes using your spreadsheet (see pic below). This used to take me several hours (6+!) using my manual method, and with the spreadsheet the results are much better as well.Previous gamma calibration
The first thing I did last night was to measure how my custom gamma was holding up which I created probably about 150 bulb hours ago. I measured the current settings and the curve was very poor.
Average gamma was 2.07 and WAY off on the top end (5-55% was in the 2.27 - 2.11 range, then things dropped pretty sharply, with 60-80% in the 2.04 - 2.0 range, 85% at 1.93, 90% at 1.9, and 95% at 1.58!).
I know that with this prior gamma calibration I couldn't get the top-end too well when I finished, although it was significantly better than this. At any rate, clearly with the top end gamma so poor there will be a much improved picture.Latest gamma calibration
So with leDahu's spreadsheet in hand I set out to resolve the poor gamma curve. I was really pleasantly surprised to see how well it came out, especially considering how easy it was to follow his procedure compared to the manual way I was doing this before.
Here is the graph with my latest results:
I started with the gamma correction value at the default 2.2 and followed leDahu's excellent instructions. The first attempt only took 15 minutes including time to run the grayscale measurements and the results were very good (despite a spreadsheet issue with #N/A being returned which I detail in the notes below).
The top end needed quite a bit more work though, along with some tweaks in the range overall, so I ran through the refinement process several times. Probably about 10 refinement cycles overall, but it was well worth it.
For reference here are the values I ended up with. These are for 5, 10, 15, 20 - 90, and 95% respectively:
50, 93, 136, 177, 258, 350, 448, 556, 668, 776, 897, and 956.
By the time I finished up last night it was too late to watch any material, but at a very quick glance the picture definitely now has more pop and depth to it. I look forward to checking out the results more fully tonight.
Here are a few points in particular:
- I encountered a small issue with the spreadsheet
. If you enter a value less than 1.8 in any of the cells in row 28, then the corresponding cells in rows 29 and 31 show as "#N/A". I guess this is because the lookup table is set to work only with values up to 1.8? In my case I had three values in row 28 (the measured gammas for 85%, 90%, and 95%) under 1.8. So to work around this I used 1.8 for the first pass and then refined it with the subsequent measurement. Hopefully leDahu can update this to support values below 1.8, perhaps as low as 1.4 (or lower?) to handle this situation.
- I took leDahu's advice and worked from the top down. This is really critical to getting the top end as perfect as possible. As he mentions it is very sensitive at the top end.
- I found it very interesting that when looking at the individual R, G and B lines on the gamma graph, these are perfectly converged from 5-50%. Then starting at 55% they start to diverge, first gradually and then continually, even more so as you move to 95%. HOWEVER, this does not occur on the RGB levels graph (which remains flat across 5-100%) and the dE is all < 3 through the range. For instance at 80% R, G and B gamma is 2.32, 2.21, and 2.13 respectively. And at 95% its the widest, with R, G and B measuring 2.7, 2.4, and 2.09. Do you find this odd? Some of this may be to custom gamma tweaks I made to RGB to get the grayscale flat, come to think of it...
- There were some slight dips at 75% (2.19) and 85% (2.16). But of course no controls are available for there and I suppose this is close enough. I guess all things considered it is a testament to JVC's excellent algorithm that all the other half steps (25%, 35%, 55% etc) track so well.
- I have heard (mostly) good things about the RSx series and higher gammas and have always wanted to try 2.4 or 2.5. However the calibration process was way too much work to go through, especially considering I may have found that I didn't like the results. Therefore I never bothered and stuck with 2.2. Now thanks to this spreadsheet I should be able to dial in a very nice 2.4 or 2.5 curve in less than an hour. I am really looking forward to experimenting with that and seeing how I like these alternate gammas.
- Per the above note I plan to try a 2.4 and 2.5 gamma curve, but with 5% set to use a gamma point based on a 2.2 curve (to try and improve shadow details with these higher gammas, per other things I have read). I would love to hear your feedback on how you think 2.4 and 2.5 looks on the RS20.
Again I want to thank leDahu for his excellent spreadsheet and others here who have contributed to the excellent discussion. This spreadsheet is my new favorite tool (if you haven't been able to tell yet
) and I look forward to more experimentation now with 2.4 and 2.5 curves.
As always your comments and feedback are encouraged and welcome!