ALEXA SXT / SXR Frequently Asked Questions
Welcome to the frequently asked questions about ALEXA SXT /SXR.
1. ALEXA Camera Line-up and Upgrades
- ALEXA SXT EV, ALEXA SXT Plus and ALEXA SXT Studio replace the ALEXA XT cameras.
- Due to the launch of ALEXA Mini, there will not be an ALEXA SXT M.
- The original ALEXA remains in the program and gets re-named ‘ALEXA Classic EV’.
- Until ALEXA SXT is available we will continue to sell ALEXA XT cameras.
- The ALEXA Plus upgrades (ALEXA to ALEXA Plus and ALEXA XT to ALEXA XT Plus) remain in the program and are joined by the new ALEXA SXT EV to ALEXA SXT Plus upgrade.
In terms of software, the new image processing path and the pixel correction algorithm from the ALEXA 65 are being used, as well as color management and noise reduction from AMIRA.
2. ALEXA SXT/SXR Media
3. ALEXA SXT/SXR Features
Here is the short list:
- ProRes 4K recording
- Improved image quality
- New looks and smoother workflow (ASC CDL & 3D LUTs)
- Three independent HD-SDI outputs
- Faster, higher capacity SXR Capture Drives
And here is a slightly longer list with a little more detail:
- Easy in-camera ProRes 4K recording
- ProRes 4K UHD (3840 x 2160) recording format for 4K UHD TV deliverables
- ProRes 4K Cine (4096 x 2636) recording format for 4C DCI cinema deliverables
- Improved image quality
- Completely overhauled image processing chain
- Advanced pixel correction
- Optional noise reduction
- New color management
- Matches current ALEXA images, but provides the basis for radically different looks
- 3D Look-up Tables, ASC Color Decision List
- Live in-camera grading on set
- Rec 2020 gamma
- Same tools for ALEXA SXT, ALEXA Mini & AMIRA
- Super flexible on-set monitoring
- Three fully independent HD-SDI outputs
- Powerful new media bay
- Supports new high speed SXR Capture Drives (1 TB or 2 TB) via SXR Adapter
- Supports current XR Capture Drive 512 GB via XR Adapter
- Supports SxS PRO and SxS PRO+ cards via SxS Adapter 2
- Supports CFast 2.0 cards via CFast 2.0 Adapter 2
Some features of previous ALEXA cameras are not available in ALEXA SXT/SXR cameras anymore:
- ALEXA SXT/SXR cameras do not have the option of recording DNxHD, since DNxHD was simply not very popular as a recording format.
- ALEXA SXT/SXR cameras do not support the Fiber Remote option.
- ALEXA SXT/SXR cameras do not support 8, 16 and 32 GB SxS PRO cards.
- ALEXA SXT/SXR cameras do not support ALEXA Look Files with a 1D LUT. Instead, they use the new ARRI Look File 2 with ASC CDL and 3D LUT support.
- ALEXA SXT/SXR cameras do not support the SUP 10/11 CDL server functionality. This functionality has been replaced by the new AFL-2 (CDL & 3D LUT) metadata capture.
4. Sensor Modes, Recording Formats, Distribution Formats
An example: Choosing a 16:9 sensor mode on the ALEXA SXT allows the further choice of various recording formats. Choosing the 4K UHD recording format means that a 16:9 area from the sensor is read out, up-sampled in camera to a 4K UHD image and then recorded. In this case the recording format of 4K UHD is the same as the distribution format of 4K UHD.
ALEXA SXT/SXR camera support four sensor modes, 16:9, 6:5, 4:3 and Open Gate. Below is a basic guide to those sensor modes and the most often used recording formats.
The 16:9 sensor mode is most often used for TV shows that need an HD or a 4K UHD deliverable. For the 16:9 HD recording format, 2.8K from the sensor are used. For the 16:9 4K UHD recording format, 3.2K from the sensor are used. The 16:9 2.8K sensor mode can also be used to derive a 16:9 2K Cine recording format.
The 6:5 sensor mode (formerly 4:3 Cropped also) is used exclusively for any shooting with anamorphic lenses. Since anamorphic lenses squeeze the 2.39:1 image by a factor of 2, the resulting area used on the sensor has a 1.195:1 aspect ratio, which is 6:5.
The 4:3 sensor mode is as tall but slight wider than 6:5. Shooting 4:3 has become popular for VFX heavy feature films in the 1.85:1 aspect ratio (dotted line). The area above and below the 1.85:1 image is used for placing VFX markers and/or for up/down repositioning.
Open Gate uses the full sensor area of the ALEXA camera. This format has become popular for those shooting feature films in 2.39:1 or 1.85:1. The extra area above and below the image is used for placing VFX markers or for up/down repositioning. The extra resolution provides the best result when up-sampling to a 4K Cine recording format.
In the ALEXA XT cameras with SUP 11 we have introduced this mode, however, there it was still called ‘4:3 Cropped’, but that is the same thing as the ALEXA SXT/SXR 6:5 sensor mode.
We have a new online tool in the TOOLS section of the ALEXA web pages, the ARRI Lens Illumination Guide.
Every lens is brighter in the center than in the corners: that is called the lens illumination. To get a feeling for how lenses perform in Open Gate, you first choose a sensor mode and what framelines you want to check out. Then you choose a lens model, focal length, iris and focus setting, which are all parameters that affect lens illumination. The resulting image will show how the illumination falls off towards the corners and if you get vignetting. We have most ARRI lenses in there already, but the guys are still shooting, so we will add more lenses as time goes by. You can see the result right there on the screen or save the images as a JPEG file.
Some lenses do better and others worse. One of the lenses that does really well (even though it is not in yet) is our Ultra Wide Zoom UWZ 9.5 – 18; it was designed for a large image circle. Most primes under 18 mm have an issue shooting Open Gate, so the UWZ really solves the question of how to shoot wide angle with Open Gate.
ALEXA SXT/SXR cameras can record ProRes in HD, 2K Cine, 3.2K, 4K UHD or 4K Cine. And they can do that with all high-end ProRes flavors from ProRes 422 to ProRes 4444 XQ.
In addition, we are working on a number of improvements and new recording formats, which we will announce once all tests have been concluded to our satisfaction.
5. ProRes 4K
The short answer is that our understanding of what is important to create a good looking image has changed, technology has advanced and the ALEXA overall image quality is so good, that it up-samples beautifully.
Here is the long answer:
Scientifically, if you want the best resolution of a black and white test chart, you should over-sample, i.e. have more photosites on the sensor than in your recording format. However, an image is not just resolution and, if I may quote Rodney Charters here, movie making is not a science project. Some people talk as if all a cinematographer does all day is shoot black and white charts, and resolution is the most important image quality parameter. But that is not the case, and in fact there is so much more to it that it is crazy to look at just one aspect of the image, i.e. resolution, and make all decisions based on that. Parameters like dynamic range, noise, skin tone reproduction and the quality of the debayer are actually much more important than just resolution.
And the technology has changed. Debayering has gotten much, much better, the electronics are much more powerful and we have learned a lot about in-camera image processing and up-sample algorithms. We have a whole color science department that continually pushes the envelope of what is possible, and that is very, very important. They came up with our in-camera up-sample algorithm which is just fantastic.
So at some point we entertained the idea to do this mild up-sample from 3.2K photosites on the sensor to 3.8K (= 4K UHD) pixels in the file. And there were many inside ARRI who were opposed to that. But we have learned that the theory will only get you so far and at some point the only way to really know is to shoot a test. And the results looked great. In fact, we compared it to some ‘native’ 4K images from other cameras and our up-sampled images looked as good, if not better. That convinced everybody within ARRI that it’s possible to do a mild up-sample of 1.2x and still get the beautiful images everyone is used to from ALEXA. Now we have an answer for those who need to record a 4K image, be that in 4K UHD or 4K Cine.
The ProRes 4K UHD recording format (3840 x 2160, 16:9) is designed for a 4K UHD TV distribution format (3840 x 2160, 16:9). ProRes 4K UHD is derived from 3200 x 1800 photosites on the sensor in 16:9 sensor mode. These are the same values as used in AMIRA and ALEXA Mini.
The ProRes 4K Cine recording format (4096 x 2636, 1.55:1) is designed for the 4K DCI cinema distribution format container (4096 x 2160, 1.9:1). ProRes 4K Cine is derived from 3414 x 2198 photosites on the sensor in Open Gate sensor mode. ProRes 4K Cine is unique to the ALEXA SXT/SXR cameras in ARRI’s line of cameras.
Both formats use the same high quality 1.2x up-sample filter.
6. Current and Future ALEXA Sensors
Second, the photosite design of the ALEV 3 sensor is unique. That design provides the great dynamic range and the highlight handling that the ALEXA has, it provides the sensitivity, the low-noise floor and the beautiful skin tones. This sensor design combined with the ever improving processing chain has stood the test of time. So far we have not seen any camera that comes close, so we think we have a really unique piece of technology here