Cine Gear Expo Sees 8K Demo
The Cine Gear Expo 2023 event took place in Los Angeles at the beginning of June and one of the exhibitors was Pawel Achtel of 24X7. He showed the 24X7 65MP movie quality RAW camera with support from 8K Association member, Samsung. 65 megapixels is, of course, twice the number of pixels of 8K. Samsung provided an 8K QLED TV to show the quality that is possible to extract from the camera. We spoke to Achtel to understand better what his camera does that is different from other capture devices.
First of all, Achtel commented on how fantastic the result was that he got from the Samsung TV at the event. One of the 8K items of content that he has licensed to the 8K Association for demonstrations includes a young girl’s face and he told us that it would be ‘very easy to get the color wrong’. However, the TV was easily adjusted to give very accurate results. As we discussed with him, Samsung has actually had some of its Neo QLED TV range certified by Pantone as being very accurate for skin tones, so perhaps this should not have been a surprise.
Fixing the Color
One of the features of the camera is that it uses Direct Scene-Referred (DSR) color workflow. That is to say, when the camera is used, it can capture a known color checker target and then it will generate an input device transform that will map the RAW data from the sensor to CIEXYZ colour space. It takes around 20 seconds. This gets around the problem that can happen if you calibrate the input with just a simple white point color temperature measure. As he said, very often the illumination on a scene is from devices such as LEDs that have a very ‘spiky’ output. This is a well-known problem, when scenes, or displays, are illuminated by different spectra. The color can measure the same, but look different.
Mapping the input device transform (IDT) means that there is no need to color correct the content for color accuracy. Scenes captured under different illumination will automatically be colorimetric so that colorists in post-production can apply their chosen creative ‘look’ consistently rather than having to color correct the images first. Of course, there might be times when you want to capture a particular light such as sunrise or sunset scenes, so then you would not correct it. Further, there are some conditions when you might not be able to perform the mapping and then you could use a standard profile. Achtel confirmed that colorists often ask him why nobody had done this in camera mapping before!
Furthermore, the DSR workflow avoids other problems in color grading, where chromatic adaptation can cause gamut shifting or clipping, especially in the red and blue channels. If you adjust for less saturated areas of the image, Achtel explained, it can cause more shift of saturated blue and red towards magenta. The color accuracy of the camera, he said, is ‘as good as it gets’.
Reduces Grading Problems
However, much of our discussion was about the issue of resolution. Achtel said that ‘resolution is for bean counters’. The real issue of image quality is the actual sharpness, which is measured as Modulation Transfer Function (MTF) – that is to say, the level of contrast as a function of spatial frequency (detail). The 8K Association has previously published an article on work that Achtel has done to measure the MTF of other cameras.
The sensors come from specialist supplier Gpixel and they have extremely high contrast photosites – as good or better as some of the best photo-sites that are 10 times larger in size. Achtel’s company works closely with the Gpixel Inc in Belgium and South Korea to get the best out of the sensors, which are used in other applications including satellite and military imaging. The sensors can achieve 40% micro-contrast at Nyquist spatial frequencies and that compares to around 35% that he has measured on ARRI LF camera and as low as 0% on some other high-end digital cinema cameras!
You Need Good Algorithms
You need a good de-Bayer algorithm (discussed in the previous article) and the high level of micro-contrast (MTF) means that images can be de-Bayered to as high as 18.7K pixels for VFX applications, while still maintaining discernible contrast and detail. One of the key features for the 9×7 was to capture all the pixels in linear, uncompressed, RAW format with no additional processing. That is a challenge as there is a lot of data to be extracted, displayed and stored in real time.
The data coming from the sensor is linear and initially the camera could capture around 13 stops of dynamic range, against Arri’s cameras at around 14 and Red at ‘a bit less than 14’ which was measured using Arri DRTC dynamic range targets. The 9×7 was not doing any highlight reconstruction initially, but the firm has spent a lot of effort and expense in the last year to develop this technology. As a result, Achtel now claims a gain of an additional 2-3 stops without loss of color or resolution. Achtel told us that the sensors were fitted with a very good Color Filter Array (CFA) – the best he has seen and he can get away ‘without an IR cut’.
Real Time Processing a Challenge
The amount of image data coming off the sensor means that there is little scope for on-board processing in real time. However, a lot of post processing can be done in camera, such as generating dailies and transcoding. The volume of data is high, but you can back up the data on to external storage without a workstation by simply connecting external storage devices directly to the camera. Transcoding and dailies can also be performed on a separate DIT workstation. “You don’t need a big system’, he said, although faster I/O helps.
The camera, which costs around $200K depending on options, is generally a rental item for most content creators. It is regularly used for giant screen productions and for creating high resolution VFX plates. ACHTEL Pty Ltd is a small company that relies on a number of partners and technologists around the world. Increasing contacts with these partners is why the firm went to the Expo – it is based in Sydney but is moving to Hobart, Tasmania.
ACHTEL has worked with brands including Samsung in the past to create content that helps to show how good 8K can be. There are real challenges in getting lenses that are good enough for the sensor. Achtel said that some lenses are very expensive but are as ‘soft as butter’. You also have to be careful with diffraction limiting effects if you start to stop lenses down significantly.