Welcome to our community

Be a part of something great, join today!

Log in
  • 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 :)

Alexa sensor and the Dragon sensor

Michael Tiemann said:
In other threads, Graeme Nattress has claimed that bayer-pattern sensors achieve 70.7% of monochromatic sensors at a reasonable (MTF50?) level. Which means that 2880 pixels should have a horizontal resolution of 2036. That's close enough (99.4%) to the 2048 of DCI 2K to really not make a difference. From an information-theory point of view, scaling down 2880 or 4880 or 8880 pixels to 2048 is not going to give measurably different resolution at 2048 pixels.

At 4K DCI, it's a totally different story. In that case you need 5793 pixels to get a clean 4096 DCI at a "good" MTF level. With up to 6144 pixels, DRAGON far exceeds (> 6%) that number. If 4K matters to you, and you can resolve 100 lp/mm edge-to-edge, DRAGON will wipe the floor with Alexa.
Click to expand...

The ~70% figure refers to a naive demosaic approach to theoretically what limiting luma resolution can be achieved from a bayer CFA. That would apply to all bayer CFA sensors. Better demosaics can lead to a higher figure, and stronger optical filtering can obviously reduce this figure. MTF50 is always going to be an awful lot lower than the limiting resolution figure.

I dug up my old measure of this that Jim shot with Leica glass on Alexa and Epic MX. Limiting resolution on the Epic was close to 5k, and MTF50 around 2.5k. On the Arri (shooting 2.8k because they didn't have the newer modes working back then) MTF50 was ~1.2k or thereabouts.

Hope those (albeit old) measured numbers help.

Graeme
 
Neither Arri nor Red cameras have highlight rolloff. Both cameras measure linear into the highlights as a good digital sensor does. If you think one looks better than the other in the highlights, you're talking exposure choice and grading.

Graeme
 
I've read multiple times that there is a low contrast filter in the Alexa. I don't know the details, but looking at the images I would bet it has.
 
It certainly looks that way. You get halation around strong lights that is pretty obvious.

Graeme
 
Thank you for the infos Graeme. Always interesting to read you around here.
 
Last edited:
I have an Alexa mini or Amira should red want to compare newer arris I'd be happy to collaberate and live near NYC red store... Been meaning to go there and see weapon anyway.. But am authentically interested in knowing if the uprez or 4/3 sensor affect anything res wise? I'm sure the uprez and 3.2k won't resolve as well, but curious enough to bring it to know more from experts on red team? Thanks
 
Can you shoot me a link to the recent rumors? Thx
 
Christoffer Glans said:
But if we have a set with enough lights to do creative lighting to the best of our ability, how would the thought process be between the cameras and sensors if there's a directors vision already set before shooting? Cause the process seems to be exactly the same with either camera so what is it that makes any difference between these sensors? How can we spot the difference between them in the final result? What exactly, to our creative eyes (not scientific) is the difference between these two sensors?
Click to expand...
I believe Geoff Boyle over on the Cinematographer's Mailing List has gone into this in detail, shooting both charts and sample scenes with different cameras (particularly Alexa and Dragon) to show equivalent exposure range and colorimetry.
 
Arri really did great on the default "out of the can" looks and whatever they do to the image in-camera before recording. With RED, to squeeze all the sweet juice out of the fruit you need to take the untouched raw "negative" and "develop" it yourself. Some people think that Red cameras not having internal noise reduction is a bad thing too, others disagree and use flexible NR tools in post. I'm so glad there's a bunch of really fine digital cinema cameras out there to choose from.
 
Vadim Bobkovsky said:
Arri really did great on the default "out of the can" looks and whatever they do to the image in-camera before recording. With RED, to squeeze all the sweet juice out of the fruit you need to take the untouched raw "negative" and "develop" it yourself. Some people think that Red cameras not having internal noise reduction is a bad thing too, others disagree and use flexible NR tools in post. I'm so glad there's a bunch of really fine digital cinema cameras out there to choose from.
Click to expand...

Yes, and I chose RED. :)
 
I think one of the strongest features of the Alexa's sensor, and what I'm pretty sure is the reason it's able to produce such nice highlight roll-off is the DGA (Dual Gain Architecture) signal path from it's sensor. It basically processes 2 separate readings per pixel. One at a higher ISO, and one at a lower ISO to put the information back that might have been clipped. It's basically the same thing as an audio recorder would do by recording 2 tracks from 1 mic with one slightly lower levels as a safety just incase a level clips. I also remember reading something somewhere about how it saturates color. Their color science is fantastic and they do something with saturation where it keeps it looking natural. Can't remember specifics.
 
Alex DelVecchio said:
I think one of the strongest features of the Alexa's sensor, and what I'm pretty sure is the reason it's able to produce such nice highlight roll-off is the DGA (Dual Gain Architecture) signal path from it's sensor. It basically processes 2 separate readings per pixel. One at a higher ISO, and one at a lower ISO to put the information back that might have been clipped. It's basically the same thing as an audio recorder would do by recording 2 tracks from 1 mic with one slightly lower levels as a safety just incase a level clips. I also remember reading something somewhere about how it saturates color. Their color science is fantastic and they do something with saturation where it keeps it looking natural. Can't remember specifics.
Click to expand...
This?
http://www.dvinfo.net/article/production/camgear/what-alexa-and-watercolors-have-in-common.html
 
If I remember correctly, the Alexa color science locks in saturation once an exposure hits 50% luminance, instead of saturation and luminance having a 1-1 correlation throughout the exposure range.
 
"the Alexa color science locks in saturation once an exposure hits 50% luminance, instead of saturation and luminance having a 1-1 correlation throughout the exposure range." - it might appear so, but the conclusion is based upon a lack of understanding. Let me explain:

Imagine an RGB cube. On one corner we have black, and opposite that white. Now stand up the cube on the black corner, with the white corner vertically above it. Now around the middle we have the remaining 6 corners of the cube, fully saturated red, green, blue, cyan, yellow and magenta.

Now, let's think that the brightness of a colour is how high it is. Obviously the white corner of the cube represents the brightest colour the cube can store. Necessarily any colour that has more saturation than white is less bright than max white - just think how the "top pyramid" of the cube slopes away from max white. So if you want a saturated colour, it can never be brighter than half-way up. Similarly if you want a bright colour, it must be reduced in saturation as the brightest possible colour is pure white.

Now you can see that saturation falling-off with increasing exposure is a natural consequence of an RGB model and not something engineered into things.

Graeme
 
Very interesting! Thank you for the clarification sir!

Is that slope that you describe a constant across different camera systems? Or do the engineers behind the camera have the ability to decide where and when that slope takes place?

Also, is the slope that you are describing linear or logarithmic?

Thank you in advance for any information you can share!
 
It's not a camera thing. It's an RGB colour space thing. What changes this is how you deal with the display. One of the big benefits of HDR displays is that they can not just display brighter colours but brighter colours that retain their saturation.

Some image processing will seek to subvert this natural effect of RGB colour cubes by reducing the brightness of saturated colours so that they retain more of their saturation. This is probably an aspect of the "video look".

Graeme
 
Great to know! Thank you for sharing your expertise! Much appreciated!
 
Misinformation abounds, so I try to do my little bit :-)

Graeme
 
You must log in or register to reply here.
Back
Top