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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

DR ..a good discussion!!

Luigi,


I have absolutely no idea of how to use a Xyla Chart. You may have to wait on Aaron, Les, Sabovic..etc for this test.
 
Rand, the Xyla is a backlit chart that allows you to measure how many stops of exposure you can get with any given sensor. The first, brightest square is set just at or below clipping, so you can then count back down to see how many stops you get before the image becomes too dark or noisy.

Also, if you apply a look from a grade you've used elsewhere to the Xyla test chart result, you can see how much of the full range of the sensor you've actually used in that grade.
 
40737653080_2c01ccc44b_b.jpg


I'll check the xyla test in a bit!
 
Les,


Thanks a lot!!! Let me figure out exactly how to do this and try to post.



Rand
 
Les,



This was grade for this Monstro image that I applied to the 8k 2:1 Xyla. I usually delete my grades so I will have to go back a probably redo some for this test. This was one of a few I didn't delete out of Redcine-X yet.



A001_C004_010386.0000956_F.0000000.jpg



A001_C001_0112_CW.0000000.jpg
 
Here is the redo of the underexposed Venice Image corrected.


New_luigi_girlfriend_1.1.4.jpg




5k_2.1_1.5.1.jpg
 
Interesting to see that Rand, although comparing the graded response to the base Xyla result was just something I mentioned in passing, sort of like a little detail or info nugget to look at when grading or generally checking things out. Mentioning using the Xyla results like that was also a bit of a counterpoint to the 'my exposure range is bigger than yours' kind of thing you can get when using charts to compare camera's, as the absolute exposure values can easily get compromised during the creative process.

Not saying it isn't useful information or a good way of comparing things though...











800ISO
 
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Les.

I don't even know if I did it right or not. I applied the 8K Monstro grades to the 8k 2:1 Xyla and, I assume the Venice grades to the 5K WS 2:1
 
Les,

I believe I misunderstood. Your examples make better sense. I thought Luigi wanted to see some kind of error or how the different grades affected the different sensors. From what I am understanding from your examples, It was for a general assessment not a specific one.
 
rand thompson said:
Les.

I don't even know if I did it right or not. I applied the 8K Monstro grades to the 8k 2:1 Xyla and, I assume the Venice grades to the 5K WS 2:1
Click to expand...

Don't worry about it Rand, it's a trivial thing no-one else needs to see, or even anything you need to check out. It's simply a way of seeing in a chart what effect your creative grade has had on the full exposure range (ie. how much you've crushed or pushed the lows and highs). The unique thing about it is that it's a comparison only the Xyla chart lets you make because of its particular way of presenting the exposure information. So, you have the properly exposed Xyla chart result, which is the same as or similar to the base image you're grading from, then you compare it to that same result but with your grade applied. From there you can maybe make some grading or shooting decisions based on the differences you're seeing.

Edit - Just saw your second post. Yes, you've got it, sorry for the confusion.
 
Thanks again Les!


I still need to get more technically savvy as you and others on this board are. Les, you should put together an educational DVD or Bluray on this subject, I'd buy One !
 
Les Hillis said:
Interesting to see that Rand, although comparing the graded response to the base Xyla result was just something I mentioned in passing, sort of like a little detail or info nugget to look at when grading or generally checking things out. Mentioning using the Xyla results like that was also a bit of a counterpoint to the 'my exposure range is bigger than yours' kind of thing you can get when using charts to compare camera's, as the absolute exposure values can easily get compromised during the creative process.

Not saying it isn't useful information or a good way of comparing things though...



800ISO
Click to expand...

And the winner is..... Venice LowLight.
Didn't expect that to be honest.
 
Thanks Rand, but all I know for sure is there's a whole lot of stuff I don't know.

Here's a more direct comparison of Luigi's Xyla charts though-



I'd still pick the Monstro myself, if I had to choose just one.
 
I had an Alexa chart somewhere on my hard drive so I threw that in.

First, I processed all clips to ARRI Alexa/Log-C color via a color space transform in Resolve to avoid any visual bias with different gamma curves showing each chip at different brightnesses. Then I white balanced all clips to the 6/20 chip via the raw tab. I also matched their exposures via these settings:

Alexa - ISO 800
Monstro - ISO 2500 +0.15 exposure
Gemini - ISO 1600 -0.05 exposure
Gemini Low Light - ISO 5000 +0.24 exposure
Venice - ISO 1090
Venice 2500 base - ISO 5880

Unless I messed something up, this chart at viewed at 100% scale should represent 1:1 pixels for a 4K delivery. These include the first clipped chip, as well.
27680418897_3f1a41f222_o.png


Provided the methodology for shooting these charts was sound, this should provide a clearer demonstration of what's going on. And when white balanced, you can see how the black balance goes off on some cameras. What the Alexa and the Venice do nicely is a very neutral greyscale while the red cameras show color shifts - color balance the top end and the bottom end goes another way.

The Venice appears to have some rolling/banding/frequency noise going on - not fixed pattern. Luigi provided two frames and the horizontal lines move vertically frame to frame. I also am not seeing very much CMOS smear as was suggested. It's probably a dark spot in the rolling noise causing the illusion - won't know for sure until we have a few seconds worth of footage to look at with some vertical panning included.

All I know is this many discrete stops is impressive for all the cameras involved. I can see 16 stops on all cameras. I can also just barely make out the division line before the 17th stop. Now, who's to say what makes a "usable" stop, but that's for you to decide as the artist.
 
Les Hillis said:
Thanks Rand, but all I know for sure is there's a whole lot of stuff I don't know.

Here's a more direct comparison of Luigi's Xyla charts though-



I'd still pick the Monstro myself, if I had to choose just one.
Click to expand...

What's with the big difference in brightness between standard and low light modes in your image? Are these charts not all aligned?
 
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