SIGMA fp fpSup Mods Add OG4K Open Gate – Lossless CinemaDNG, Gyroflow Data, RAW Monitoring

How ToCamera Hacks

by Nino LeitnerToday

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The community project fpSup now gives the original SIGMA fp five extra CinemaDNG formats, up to OG4K at 3840 x 2560 from the full 3:2 sensor, plus lossless compression with the camera’s own hardware codec. Gyro data for Gyroflow, a RAW monitoring view and an anamorphic de-squeeze preview complete a list of features that SIGMA never offered on this camera.

This is part one of our series on camera firmware hacks; our overview article explains how the current wave of AI-assisted mods started. When we reported on the SIGMA fp open-gate hack at the end of September, the news was a single 3K 3:2 recording mode, first shown by developer Vitaly Li and then released in a second build by the fpSup project. One month later, fpSup has turned into a set of tools that you pick in a web page called fpSup-Merge and copy to one SD card. Johnnie reviewed the fp for CineD in 2019, with lab results, and I have to say, I did not expect this tiny camera to get a second life of this kind.

Everything below works on one camera and one firmware only: the original SIGMA fp with firmware Ver.5.02. The project is explicit that this means “not 5.02 or newer”, and that the fp L, with its different sensor, is not supported at all. All of the tools are labeled test, alpha or beta builds.

Why this works without flashing the camera

The way into the fp is unusual. According to the fpSup documentation, firmware Ver.5.02 contains a factory and debug shell with 77 commands, which can read and write memory, set registers, change the sensor’s readout modes and set menu values. At startup, the camera looks for a file called AutoRun.txt on the SD card and runs every line of it through that shell, with no confirmation step. The developer, who goes by bei, 夏曉雨 or ijigen, says AI tools helped decompile the firmware and find this path.

fpSup uses the AutoRun.txt as a loader: it writes a small routine into unused RAM, which then loads the actual tools from the card. Nothing goes into the camera’s flash memory. Without the card, the fp boots stock. There is one detail to get right on removal, though. When you select a new mode in the camera’s own menu, the camera stores that choice in its normal settings, so the project tells you to set the menus back to stock options before you delete the files.

Five open-gate and crop formats

The Res-Custom card combines five recording formats, which appear next to UHD and FHD in the camera’s Settings and Quick Set menus. OG2K records 2000 x 1334 from a 3 x 3 binned readout of the full 3:2 sensor, at 23.98 to 100fps. OG3K records 3008 x 2000 from a 2 x 2 binned readout, also up to 100fps. S16 is a 1:1 window of about 2.9x crop at 2096 x 1238 in 16:9, again up to 100fps. The two new top formats, OG3.5K at 3456 x 2304 and OG4K at 3840 x 2560, use a full 1:1 readout that is then scaled in the camera’s image processor, and they run at 23.98 to 29.97fps. S16, OG3.5K and OG4K are the work of developer Jose Hurtado, whose timings and readout windows fpSup uses unchanged.

The open-gate formats borrow sensor modes from stills, and Jose found that their black level steps from frame to frame at high ISO, which shows as flickering shadows. His fix, which turns on the video clamp, is part of all five formats. Rolling shutter also changes with the mode. fpSup gives 8.3ms for OG2K and 12.44ms for OG3K, compared with 21.1ms for the fp’s stock UHD CinemaDNG mode, which is a nice side benefit of the binned readouts.

Storage is the limit

The data rates explain why the fp never recorded these formats officially, at least in my opinion. In 12-bit at 24p, fpSup lists 98 MB/s for OG2K, 95 MB/s for S16, 219 MB/s for OG3K, 287 MB/s for OG3.5K and 354 MB/s for OG4K. A UHS-II SD card that the developers measured wrote 94 MB/s, and an external SSD on the USB-C port wrote about 390 MB/s. So OG3K, OG3.5K and OG4K need the SSD, and OG2K and S16 sit at the edge of what an SD card can do. If the storage is too slow, the camera stops recording after a few seconds, once its RAM buffer is full.

OG3.5K and OG4K can now record 12-bit in addition to 8-bit and 10-bit, and with Crop Mode switched on, they record the center of the sensor 1:1 at the same DNG size. The project lists what has been tested: 12-bit OG3K and S16, and 8-bit OG4K and OG3.5K recorded with correct DNG sizes and clean pictures. Crop Mode with the two large formats, 100p on OG2K, OG3K and S16, and standby framing on OG4K were not tested on a camera at the time of writing.

Lossless CinemaDNG from the camera’s own codec

For many fp owners, fpSup-Lossless is perhaps the more useful tool. The fp has a hardware codec for lossless compression that the stock firmware never uses for video. fpSup-Lossless adds a Lossless RAW row to the SHOOT menu and, according to the project, typically turns a 3K 12-bit frame of 9.1 MB into about 3.2 MB without changing a single pixel value. When the codec cannot finish a frame in time, that frame is written uncompressed, so a clip can mix both kinds of frames, but no frame is dropped. Community member CorNy found that DaVinci Resolve plays such mixed clips without flicker only when the first frame is uncompressed, so every take now starts with an uncompressed frame.

The tested list includes OG3K 12-bit 29.97p to SD in takes of 10 to 15 seconds with about 92% of frames compressed, FHD takes at 24p and 59.94p with every frame after the first compressed, and an earlier build recording 3K 12-bit 48p to an SSD for 15 minutes. UHD, 10-bit and other frame rates are not tested, and a reported freeze at 100p with 10-bit and Lossless switched on is still under investigation. Since the compression brings OG3K close to SD card speeds, Lossless and the open-gate formats are a natural combination, and the project confirms that both run together on one card.

Gyroflow data, RAW monitoring and more

Gyro2 writes the fp’s gyro and level data into every CinemaDNG frame. A modified version of the Gyroflow OpenFX plugin for DaVinci Resolve, published by fpSup under the GPL-3.0 license, reads the data from the frames and stabilizes the clip, with no sync step and no lens profile for electronic lenses. For manual lenses, you enter the focal length in the plugin. The Mac version is not notarized by Apple and has been tested on Apple silicon only.

RAW-View adds a RAW row to the COLOR menu. In 12-bit CinemaDNG, the screen then shows the RAW image that the camera is about to record, with the recording gain applied in standby and sensor saturation shown as white, so what clips on the screen clips in the DNG. Its display curves build on cinematographer Ole Berek’s SIGMA fp Rec709 LUT guide, and according to the project, live view resolves about 10.9 stops below clipping. A test build called fpsup-desqueeze shows a de-squeezed anamorphic preview at 1.33x, 1.6x or 2.0x, ScreenFlip rotates or mirrors the rear screen, and Tap to Zoom magnifies live view by 2x around the point you touch, with 4x and 8x on the command dial; it now also works while recording and together with the de-squeeze preview. The newest test build, fpsup-unlocked-writer, changes how the camera writes to the card: it writes the recording data without holding the file-system lock, so the two tasks run at the same time. On SD cards, it switches on by itself, and on an SSD, it needs Write Mode. My guess is that this is aimed at the formats that are close to the card’s speed limit, but the project does not publish test results for it yet. Split Record, HDRx, LUT preview and autofocus improvements are listed as in development.

A small user base with a lot of developers

There is something special going on here. The fp was always a niche camera, and SIGMA’s last official firmware for it, Ver.5.02, dates back to 2023. Yet the fpSup project credits several outside developers and testers by name, publishes a list of what is and is not tested with every release, and gives away tools, research notes and AI instruction files for free, with a Ko-fi page to support the work. The developer writes: “I really love the fp’s design, so I stubbornly stuck with it.” I can relate to that.

My feeling is that SIGMA should take a close look at this. The SIGMA FP2 now records 6K open gate officially, so the question of whether open gate is a selling point has been answered by SIGMA itself. (A small official update for the original fp, even just the lossless CinemaDNG option, would be a nice thank-you to the people who bought into the fp idea in 2019.)

Price and availability

fpSup is free and open source, with downloads, install and removal steps on the fpSup website and source code on GitHub. It is not affiliated with or endorsed by SIGMA, and the developers warn that using it may cause failed recordings, data loss or an unusable camera. The original SIGMA fp is still listed at B&H as a refurbished body. CVP no longer lists the original fp. For more information, please visit the SIGMA website.

Are you still shooting with a SIGMA fp, and would you try one of the fpSup tools? Which format would you use first, OG3K or OG4K? Let me know what you think in the comments below!