SIGMA fp Open-Gate Hack – 3K 3:2 CinemaDNG, 12-Bit RAW, Full Sensor Readout

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by Johnnie BehiriToday

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A community-made firmware mod lets the SIGMA fp record open-gate for the first time, writing 3:2 CinemaDNG RAW at around 3000 x 2000 from the full area of its full-frame sensor. It is free, experimental, on YOUR OWN RISK, and tied to a single firmware version, so let’s take a look at what it does and where it stops.

The prototype comes from developer Vitaly Li, who shared it in a SIGMA fp user group on Facebook. It adds a 3K option to the camera’s Quick Set menu and records 3000 x 2000 CinemaDNG at 24fps in 12-bit to an external SSD, using the whole 3:2 sensor instead of the 16:9 window the SIGMA fp normally records from. User who tried the hack set the recording time to around 18 minutes and reported the possibility of a pink first frame in each clip. Note that recording directly to the SD card is not possible. The build has only been tested on firmware Ver.5.02, and Vitali Li is clear about its status: “Use at your own risk; it is still a work in progress.”

Officially, the fp has never recorded an open-gate. Since our review of the camera in 2019, SIGMA added a long list of features through firmware, and Ver.5.00 brought open-gate frame lines for the ARRI ALEXA LF and ALEXA Mini LF, with anamorphic squeeze factors from 1.25x to 2x, to the Director’s Viewfinder. That is a framing simulation, though. Actual recording stayed at UHD and Full HD, and Ver.5.02, the most recent official release, dates back to 2023.

How the mod gets onto the camera

Installation consists of copying two files to the root of an SD card. The camera loads them at power-on, which is why the approach draws comparisons with Magic Lantern on Canon DSLRs: the code runs from the card alongside the stock firmware instead of replacing it.

Li credits 夏曉雨 and her Gyroflow project as the foundation for much of his work, and thanks Discord user @mev.ich for the sample footage. A gyro logger of exactly that kind is part of fpSup, an open-source SIGMA fp firmware research project on GitHub that writes Gyroflow-ready gyro data next to each CinemaDNG take. The fpSup documentation, in turn, names Li as the first person to get open-gate out of an fp.

According to that documentation, everything runs in RAM from an AutoRun.txt file, and nothing is written to the camera’s flash memory. Deleting the file and cold-booting with the battery removed returns the camera to stock. The restriction to Ver.5.02 follows from the method: the patches target fixed memory addresses, and on any other firmware version those addresses hold something else.

A second build with more frame rates

fpSup now ships its own open-gate release, OG3K, currently at v0.2.3a and labeled alpha. It stores a 3024 x 2010 raw frame with a default DNG crop of 3008 x 2000, offers 8, 10 and 12-bit CinemaDNG, and lists eight frame rates from 23.976 to 100fps. The mode appears as a native entry in both the Settings and Quick Set menus, and the camera’s Super35 crop has to be switched off for it to record.

Li describes his 3K image as downsampled from 6K. The fpSup notes are more specific about their build, calling it the native 2×2-binned readout of the Sony IMX410 sensor and not a scaled 6K image. One side effect the developers list is a shorter readout: 12.44 ms of rolling shutter for OG3K against 21.1 ms for the camera’s stock UHD CinemaDNG mode.

The list of what has not been verified is long, and the developers publish it with every release. Only 25p at a 180° shutter has passed a frame-by-frame check of the recorded files. In-camera playback and highlight headroom at 8 and 10-bit, the remaining frame rates, and sustained recording on fast media are all marked as untested, and one freeze during an OG3K take could not be reproduced. On Li’s build, some users report DNG frames that look corrupted.

Why it needs an SSD

Uncompressed CinemaDNG is limited by write speed before anything else. The fpSup documentation puts 3K open-gate at 24p at roughly 220 MB/s in 12-bit, 184 MB/s in 10-bit and 148 MB/s in 8-bit. A mid-range UHS-II card measured by the developers sustained 94 MB/s, and open-gate took on it stopped after three to four seconds once the camera’s RAM buffer filled up.

An SSD on the camera’s USB-C port reached about 390 MB/s in the same tests, which the developers attribute to the 5 Gbps USB 3.0 link and not to the drive. At 220 MB/s, Li’s 18 minutes would add up to roughly 240GB, although he does not say which drive that figure refers to.

Those measurements also show why full-resolution 6K open-gate remains out of reach. By the project’s math, uncompressed 8-bit 6K at 29.97fps would need about 735 MB/s, close to double what the USB connection delivered. SIGMA has not commented on why open-gate recording was never offered, so that reasoning belongs to the developers. For SD-only shooting, fpSup offers a separate test build called OG2K: the same field of view at 2016 x 1344 and 98 MB/s in 12-bit 24p.

What a 3:2 raw frame is good for

The appeal is sensor height. A 3:2 frame leaves room to cut both a 16:9 and a 9:16 deliverable from one take, and it suits anamorphic lenses better than a 16:9 recording: a 1.5x squeeze on 3:2 desqueezes to 2.25:1 without cropping the sides. The trade-off is pixel count. At 3008 x 2000, each frame holds about 6 megapixels, compared with 8.3 megapixels in UHD, so the mod exchanges resolution for sensor area.

For a camera launched in 2019, that is a meaningful addition, particularly for owners who bought the fp for its CinemaDNG output in the first place. It is still unofficial software, and anyone trying it should check every take before relying on it.

Price and availability

Both builds are free. Vitaly Li’s prototype is available as a download via Google Drive, and the OG3K and OG2K releases can be found in the fpSup repository, which accepts voluntary support through Ko-fi. Each requires a SIGMA fp running firmware Ver.5.02; the fp L is not covered.

For more information, please visit the fpSup project page.

This article is NOT encouraging anyone to use unofficial or unsupported firmware on their SIGMA fp cameras. Installing such firmware is at your own risk!

Do you still shoot with a SIGMA fp, and would 3K open-gate RAW change how you use it? Don’t hesitate to let us know in the comments below!