The Elphel 353 Model free software and open hardware camera is a very interesting and powerful device for film making. You can find more information about it on the Elphel Inc. Website. Please note that apertus° does not sell Elphel cameras. If you want to purchase one get in touch with Elphel Inc. directly - they ship worldwide.
The camera uses an Aptina CMOS bayer-pattern sensor with an optical format of 1/2.5" (5.70mm x 4.28mm) and a native resolution of 2592x1944 (5 Megapixels). It features a 12 bit ADC and supports: region of interest, on-chip binning and decimation. Aptina claims that the chip has 70db of dynamic range at full resolution and 76db when using 2x2 binning.
The camera has a standard C-mount but ships with an adapter ring that allows to mount CS-lenses as well.
The frame-rate at which video is recorded can simply be any value you can imagine from super slow time-lapse with just a single frame a day/week/month up to the maximum value that the sensor can provide at a certain resolution (see chart below). The frame-rate is also not limited to integer values, you can record 29.97 fps as well as 5.79 fps or any other value. The camera even supports dynamic frame-rate changes in the same video container. This allows fps ramps or any custom fps curve with scripts (we still need to integrate this into ElphelVision GUI), the camera just records on frame after the other into the video container no matter how much time elapses between the exposures.
The same way you have free choice of FPS or resolution you can freely choose the compression ratio and resulting data-rate. The compressor uses a ratio between 0 - 100, where 0 equals a very strong compression, lowest image quality and datarate and 100 results in virtually uncompressed, high datarate video with maximum possible image quality. The actual data-rate exponentially increases towards 100. This quality/compression ratio can also be dynamically changed while recording and the final data-rate also depends on the actual image content. The maximum possible datarate with Elphel 353 is currently ~144Mbit/s when recording to camera connected SATA drive and 100Mbit/s when streaming video over Ethernet. The camera internal circular buffer (short circbuffer) holds all video frames after they have gone through the internal image compressor. The disk recorder or video streamer software then takes these frames and write them to the designated media like HDD/SSD/CF Card or over the network. If the data-rate is too high the frames cannot be written to the media as fast as new frames are written into the circbuffer. The circbuffer will overflow and the recording will drop frames. This is the tricky game: on the one hand you want to push quality to the max to get best possible image quality but on the other hand if you push too far you end up dropping frames and are left with a broken video clip.
Some big camera manufacturers claim that a big aspect of their "cinema look" is the result of their specially developed gamma curve with names starting with hyper- or cine-. Truth is that you will have a hard time even finding out the actual shape of this special gamma curve.
Elphel cameras can use any custom gamma curve (generated from gamma values or any custom shape like S shapes, knees, etc. ).
The recording resolution can be freely adjusted to anything starting from 16x16 to 2592x1944 in 16 pixel steps. This includes AMAX (2224x1251), CIMAX (2592x1120), 2K (2048x1536), Full HD (1920x1080), HD (1280x720) and of course all lower resolution SD formats like DV PAL, DV NTSC, etc.
The lower the resolution the higher the maximum possible frame-rate. At the full sensor size (5 million pixels or 5 Megapixels) the maximal frame rate is 10 fps in normal color mode and 15 fps in JP4 RAW mode. JP4 achieves higher frame-rates in general as some camera internal calculations are skipped and need to be applied later in post-production (like debayering/demosaicing).
|Standard||Resolution||Record Mode||max. FPS|
|AMAX 16:9||2224x1264||JP4 RAW||24|
|CIMAX 2.35:1||2592x1120||JP4 RAW||24.2|
|Full HD (1080p)||1920x1088||RGB||25.2|
|Full HD (1080p)||1920x1088||JP4 RAW||30.9|
|HD (720p)||1280x720||JP4 RAW||60|
||640x480||RGB / JP4 RAW||126|
||854x480||RGB / JP4 RAW||110|
||720x576||RGB / JP4 RAW||100|
|PAL DV 16:9
||1024x576||RGB / JP4 RAW||84|
The RAW recording mode in the Elphel camera is called JP4 RAW. Because certain in-camera compression steps can be skipped JP4 RAW allows higher recording speed resulting in more FPS. JP4 RAW requires post-processing (the DNG Converter software) but in return offers the highest possible image quality.
The main compression algorithm used is based on MJPEG (Motion JPEG). This means that there is NO interframe-compression resulting in slow scrubbing and increased performance requirements on computers playing back the video file. With modern DSLR cameras (very popular for shooting video recently) Editors suggest to convert the footage to ProRes or MJPEG before starting editing. The Elphel camera uses this codec right away.
Red uses a similar approach with their Redcode Raw codec by utilizing Motion JPEG2000 (also called wavelet) compression.
MJPEG is not bound to any license fees and patent royalties in contrast to H264 (->Wikipedia).
H264 based codecs like AVCHD or other interframe compression codec require a lot more computing power for decoding or dedicated decoding hardware for smooth playback. MJPEG videos are lightweight and require very little computing resources for decoding. This allows us to use netbooks or tablet-PCs as viewfinder with apertus°.
SATA: Can be used to connect any external SATA device that is supported under Linux (external harddrives, raids, etc.)
Ethernet: 100MBit Network with POE (48V)
USB: USB 1.1 with 5V power supply
IDE: Used to connect internal HDD
RS232: Access to Console and debug output