Image processing hardware

ARRI's image processing philosophy is to maintain the highest quality as far as possible throughout the processing chain. This means transporting and processing uncompressed 16 bit raw data inside the camera, a task that requires enormous processing power, which is provided by the latest in processor technology combined with a super fast internal data bus. From this internal data stream the image processing hardware derives the ALEXA recording formats, including ARRIRAW, ProRes and DNxHD, the HD-SDI monitoring images and the viewfinder image.

Unencrypted, uncompressed ARRIRAW

For the absolute best in image quality, for the greatest flexibility in post and for safest archiving, the 16 bit (linear) raw data stream from the sensor can be recorded as 12 bit (log) ARRIRAW files. Nothing is "baked" into an ARRIRAW image: image processing steps like debayer, white balance, sensitivity, up-sampling or down-sampling, which are irreversibly applied in-camera for ProRes recording, DNxHD recording, HD-SDI outputs and the viewfinder image, are not applied to ARRIRAW. All these parameters can be applied to the image in post.

ARRIRAW is also an excellent future-proof archiving format. ARRIRAW is uncompressed and unencrypted, which means that anyone can access their ARRIRAW data with standard software tools in the future without any proprietary decryption or decompression. We openly publish our color science as standard SMPTE documents (Recommended Disclosure Document RDD 30:2014 and RDD 31:2014).

ProRes, DNxHD, HD-SDI and the viewfinder

While the creation of ARRIRAW inside the camera is relatively straight forward, the creation of the color images for ProRes, DNxHD, HD-SDI and the viewfinder is more complex, as the camera has to create multiple streams of full color images from the raw image data in real-time. Not only that, but the viewfinder image, the recorded image and a number of HD-SDI outputs can have different resolutions and possibly different looks and different output gamma settings. To achieve this, a powerful image processing engine debayers the raw image data, applies white balance and sensitivity and up/down-samples the images depending on the required recording/output format.

To achieve the tremendous processing power for all those steps, ALEXA's image processing hardware consists of the latest generation of FPGAs (Field Programmable Gate Array), which are re-programmable processing chips. FPGAs not only have the horse power to deliver multiple streams of the highest image quality, but their re-programmable nature ensures that improvements in processing can be made available to all existing cameras. This happened, for instance, with ALEXA Software Update Packet 11, which provided a much better debayering algorithm, instantly improving the image quality of all ALEXAs in the field.