ALEXA SXT FAQ
Questions and answers on ALEXA SXT cameras
Questions and answers on ALEXA SXT cameras
Here is the short list:
And here is a slightly longer list with more details:
New recording formats
New ARRI Look Management
Improved image quality
Single speed mode
Powerful new media bay and new drives
Live grading on set with the ARRI Look Management is supported by Pomfort LiveGrade, Codex Live, Colorfront On-Set Live, Filmlight Prelight, Technicolor DP Lights and others.
Automated dailies creation with the ARRI Look Management is supported by DaVinci Resolve, Colorfront OSD, Codex Production Suite, Pomfort Silberstack, Filmlight Daylight and others.
Editing with looks through the ARRI Look Management is supported by Avid Media Composer, Apple Final Cut Pro X and Adobe Premiere.
In all cases, check with the manufacturer to make sure you have the software version that supports the ARRI Look Management.
Some features of previous ALEXA cameras are not available in ALEXA SXT cameras anymore:
ALEXA SXT cameras do not have the option of recording DNxHD, since DNxHD was simply not very popular as a recording format.ALEXA SXT cameras do not support the Fiber Remote option.ALEXA SXT cameras do not support 8, 16 and 32 GB SxS PRO cards.ALEXA SXT 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 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 This functionality has been replaced by the new AFL-2 (CDL & 3D LUT) metadata capture.
As we like to have everything backwards compatible, using the existing adapters was our first design intention. However, since the SXR Capture Drives needed a new high-speed connector, you can end up with more electrical interfaces than is good for signal integrity. So we chose one adapter for each media family, which combines the greatest flexibility with the best signal integrity.
No, the existing XR Capture Dries will work well with the ALEXA SXT cameras. SXR Adapter and XR Adapter are included in SXT upgrades (and in new camera sets as well). SXR Capture Drives have a higher capacity and offer higher frame rates in some recording formats. The table in the ALEXA SXT Crib Sheet will give you an overview of the advantages in recording with SXR Capture Drives.
There are two methods for clearing old data from a recording medium with ALEXA SXT cameras: Quick Format and Erase. For technical reasons, most media allows only one of those methods. Quick Format erases only the file allocation table, but leaves the actual data still on the card. Quick Format is therefore the faster method. Erase takes longer than Quick Format, but ensures that all data on the card is erased. Using Erase with SxS PRO/PRO+ cards can increase their write speed.
No, in ALEXA SXT cameras, both XR and SXR Capture Drives always use RAID redundancy when recording ProRes.
No, at this point in time Capture Drives have proven to be very reliable, so we do not think this is necessary.
For technical reasons, ARRIRAW can use the full capacity of the Capture Drive, while ProRes can only use half of the drive's capacity. Rather than let half the drive go to waste when recording ProRes, we thought we might use this free capacity to add some data safety, even though Capture Drives are already one of the safest media available. This also makes sense as ProRes has a lower data rate than ARRIRAW, and so much more ProRes can be recorded onto a single drive than ARRIRAW, especially now that 1 TB and 2 TB Capture Drives are available.
No, the RAID redundancy is only available for XR and SXR Capture Drives in the ALEXA SXT.
No. Since the SXR Capture Drive dock only works in conjunction with Codex software and there is no Codex software for Windows, a Windows ARRI RAID driver would make no sense.
A sensor mode defines an aspect ratio, which defines the area on the sensor that is being captured. A recording format define what is being recorded in-camera in the file. So while a sensor mode defines a certain number of photosites on the sensor, those may be recorded straight or up or down-sampled to create the pixels of the recording format. A distribution format defines how the final product is delivered to the consumer. The contents in the recording format is often up or down-sampled, cropped, repositioned or rotated in post before it becomes the final distribution format.
An example: Choosing a 16:9 sensor mode on the camera 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.
The 4:3 aspect ratio was originally left over from the film days, and now has been put to good use by VFX-heavy feature films. Anamorphic lenses don't actually need the full width of the 4:3 image; they squeeze the 2.39:1 image by a factor of 2, and the resulting area used on the sensor has a 1.195:1 aspect ratio, which is roughly 1.2:1, which is 6:5. When shooting with anamorphic lenses in 4:3 sensor mode, you always have to crop the extra area to the left and right of the image in post, an extra processing step that is avoided by shooting in 6:5.
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 6:5 sensor mode.
To find out which lenses will work in the Open Gate sensor mode, you can use 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 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 cameras can record ARRIRAW just like the XT cameras could, but now with higher frame rates:
16:9 ARRIRAW up to 120 fps, 6:5 ARRIRAW up to 96 fps, 4:3 ARRIRAW up to 96 fps and Open Gate ARRIRAW up to 90 fps.
ALEXA SXT cameras can record ProRes in HD, 2K Cine, 3.2K, 4K UHD or 4K Cine and also in the anamorphic sensor mode 6:5 in 2K and 4K. And they can do that with all high-end ProRes flavors from ProRes 422 to ProRes 4444 XQ.
ProRes 3.2K is a recording format that is quickly gaining popularity. It is being used on major TV series like Game of Thrones, on many Amazon projects and on various feature films. The reason is that it has a lower data rate than ProRes 4K UHD (in fact about 33% less data) and thus is less expensive to record on set and to process in post. It can then be used for an HD or 2K deliverable (with extra image area for re-sizing, rotating, re-framing or stabilizing) or, with only a slight up-sample, for a 4K UHD deliverable.
With the 14 different recording formats we have in the ALEXA SXT we are offering the best image quality and most efficient workflow for the most common production, post and distribution requirements. The recording formats are optimized for different budget situations, market segments, distribution resolutions and aspect ratios, lens choices and necessary post steps including the amount of VFX work.
We are always striving to provide the best performance for each platform. As a result, there sometimes are minor differences in the actual pixel count of our recording formats. However, we are aiming to standardize as much as possible with the new cameras.
One example for this is the Open Gate format differences between ALEXA XT, ALEXA SXT and ALEXA Mini. When we first created the Open Gate format for the ALEXA XT in 2012, we had to record the full 3424 x 2202 because there are certain hardware based rules on how many pixels we can push through the camera and record. However, we found that some pixels on the edge of the frame could not be corrected by the dynamic defect pixel correction (DDPC), and so we decreed that you shall only use 3414 x 2198 of those 3424 x 2202. This 3414 x 2198 active image area is noted in metadata and the post production software should only process this area. Otherwise the very edges of the image may contain image artefacts.
While working on the ALEXA Mini and then subsequently on the ALEXA SXT, our engineers have worked out a way to make the DDPC function all the way to the edge, so now we can record and give you the full 3424 x 2202, which is, admittedly, much easier for all involved.
ALEXA SXT cameras use the extra horse power of the ALEXA 65 electronics to perform a mild up-sample in-camera, either to ProRes 4K UHD or to ProRes 4K Cine. The number of photosites are only one of many parameters that form a quality 4K image. The combination of ALEXA's best image overall image quality with the new processing chain and the relatively small up-sample factor of 1.2x preserves the fundamental qualities of the ALEXA picture that filmmakers so love.
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 pixels 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 test charts, and resolution is the most important image quality parameter. But that is not the case. Real world images are vastly different from black and white test charts, and the overall image quality is defined by many more parameters. It is crazy to look at just one aspect, i.e. resolution, and make all decisions based on that. Parameters like the absence of artifacts, dynamic range, color rendition, color gamut, noise level, temporal resolution and the quality of the debayer are actually much more important for overall image quality 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. 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 some 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 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. We are not taking the full Open Gate of 3424 x 2202 to up-sample to ProRes 4K Cine since the slightly smaller size of 3414 x 2198 gives us better results in up-sampling. ProRes 4K Cine is unique to the ALEXA SXT cameras in ARRI's line of cameras.
Both formats use the same high quality 1.2x up-sample filter.
The 4K Cine recording format contains 4096 x 2636 pixels, which is 476 lines more than the 4K DCI distribution container (4096 x 2160). This extra area above and below the image is designed for up/down image repositioning or placing of VFX markers. This is an example where the recording format purposefully contains more than is needed in the distribution format to provide for some added flexibility in post.