Questions and Answers about slimRAW

Is CinemaDNG lossless compression truly lossless?

Yes. CinemaDNG lossless compression is an entropy compression. Once imported and decompressed in your video processing application of choice the image is exactly the same as the initial uncompressed image. You can think of CinemaDNG lossless compression as an analogue to RAR or ZIP compression but taking advantage of the specifics of raw images.

Is this the same lossless compression as used in the Blackmagic Pocket Cinema Camera and the Blackmagic Production Camera 4K?

Yes, but slimRAW will generally achieve a bit better compression ratios since it is not limited by in-camera processing.

What's the deal with recompression?

slimRAW can recompress CinemaDNG/DNG files which are already losslessly compressed by other means. You can either recompress such files losslessly to optimize and shrink them further, or you can do lossy recompression for a more significant gain of disk space.

What about recompression of lossy CinemaDNG to lossless CinemaDNG?

slimRAW can transcode lossy CinemaDNG from Blackmagic cameras or from the lossy compresion modes of slimRAW itself to standard lossless CinemaDNG. The intended use of this feature is import of Blackmagic lossy raw and slimRAW'ed lossy archives in applications which only support lossless CinemaDNG (like Premiere, After Effects, etc).

Note that transcoding from lossy to lossless will usually increase size significantly. Also note that lossy to lossless transcoding doesn't mean that the initial lossy compression is somehow reversed, but merely that the raw image is re-encoded as widely compatible standard lossless CinemaDNG.

What compression ratios does slimRAW achieve?

CinemaDNG lossless compression ratios are not fixed and depend largely on the amount of image detail. Footage from cameras with anti-aliasing filters and images containing larger out of focus areas will compress better. Compression ratios ranging from 1.5:1 all the way to 2.8:1 can be achieved, resulting in reduction in data size ranging from 66% to 35%.

When doing constant bit-rate lossy compression, slimRAW targets the user specified compression ratio (currently, a choice of 3:1, 4:1, 5:1 and 7:1).

As with lossless compression, variable bit-rate lossy compression ratios are not fixed. VBR HQ lossy compression will typically result in average compression ratios in the range of 3:1 to 4:1 (but may get as high as 5:1). VBR LT lossy compression will typically achieve 4:1 to 6:1 (but may get as high as 8:1). These ratios are based on uncompressed input sizes.

What recompression ratios does slimRAW achieve?

When losslessly recompressing CinemaDNG footage that is already losslessly compressed slimRAW can further reduce size up to 20%. For losslessly compressed footage from Blackmagic cameras typical reduction is 2.5-5%. For losslessly compressed footage from DJI Zenmuse X5R typical reduction is 6-15%.

When doing lossy recompression the resulting ratio will depend on the level of compression in the source files. For example, if the source is 1.5:1 losslessly compressed, and 3:1 is selected as target, then the result will be approximately 2:1 (for a total of 1.5*2 = 3:1), or size reduced down to around 50% of the original size.

Tell me more about the different compression types in slimRAW.

Read more about the compression modes in slimRAW here.

What happens with the metadata in the original CinemaDNG files?

All embedded metadata is preserved in the compressed CinemaDNG output. This includes all color related metadata, time codes and frame rate metadata.

What CinemaDNG footage and cameras are supported?

Most 8-, 10-, 12-, 14- or 16-bit standard uncompressed CinemaDNG or DNG footage. Cameras and recorders outputting this raw format include:

  • Digital Bolex D16;
  • Sigma fp;
  • Sigma fp L;
  • Sony FS5, Sony FS7 and Sony FS700 2K and 4K uncompressed CinemaDNG raw video recorded on Convergent Design Odyssey 7Q/7Q+ or Atomos Shogun/Shogun Inferno/Shogun Flame;
  • Canon DSLR Magic Lantern RAW/MLV raw video, converted to uncompressed DNG or CinemaDNG;
  • uncompressed CinemaDNG from Kinefinity's Kinemini 4K, Kinemax 6K and KineRAW cameras;
  • DJI Zenmuse X5S;
  • DJI Zenmuse X5R;
  • DJI Zenmuse X7;
  • Panasonic VariCam LT raw recorded through Convergent Design Odyssey 7Q/7Q+;
  • Panasonic AU-EVA1 raw recorded through Atomos Shogun Inferno/Sumo19;
  • Canon C300 Mark II and Canon C500 recorded on Atomos Shogun/Shogun Inferno/Shogun Flame;
  • Blackmagic Design Cinema Camera (pre-firmware 2.1);
  • Achtel 9x7;
  • Ikonoskop A-Cam dII;
  • Indiecam indieGS2K and indiePOV (uncompressed 12-bit CinemaDNG video as exported by Indiecam Instant-RAW software);
  • uncompressed DNG frame stacks from Fastec Imaging TS and HiSpec series cameras (10-bit in a 16-bit container and 8-bit).

Losslessly compressed CinemaDNG video from:

  • Blackmagic Pocket Cinema Camera,
  • Blackmagic Cinema Camera (firmware 2.1 or newer),
  • Blackmagic Production Camera 4K,
  • Blackmagic URSA,
  • Blackmagic URSA Mini,
  • Blackmagic Micro Cinema Camera,
  • DJI Zenmuse X5S,
  • DJI Zenmuse X5R,
  • DJI Zenmuse X7,
  • most other standard compliant losslessly compressed CinemaDNG/DNG files, including DNG raw stills.

Lossy CinemaDNG from:

  • Blackmagic Micro Cinema Camera,
  • Blackmagic URSA Mini,
  • Blackmagic URSA.
Is slimRAW only useful with footage from the supported cameras list?

slimRAW can be used to safely offload or copy any kind of footage or any kind of files with checksums generation and verification. Checksums help ensure that data is safely copied and also allows for subsequent integrity checks through post and archiving. None of the data integrity features of slimRAW depend on a specific input file format. The supported cameras list only relates to slimRAW's compression functionality and lists the sources of uncompressed CinemaDNG/DNG footage supported by slimRAW. Any files or footage from other cameras will be safely copied to the output in their original form. See the user guide for details.

Which video processing applications support losslessly compressed CinemaDNG footage as output by slimRAW?

Blackmagic Design DaVinci Resolve, Blackmagic Design Fusion, Adobe Premiere Pro CC, Adobe SpeedGrade CC, Adobe software using the Adobe Camera Raw import engine (Adobe After Effects, Adobe Photoshop, Adobe Lightroom), Assimilate Scratch, FilmLight Baselight, The Foundry NUKE, Lightworks. Any other software conforming to the CinemaDNG standard and importing standard losslessly compressed CinemaDNG.

Which video processing applications support lossily compressed CinemaDNG footage as output by slimRAW?

Currently lossy CinemaDNG is supported by Blackmagic Design DaVinci Resolve and Blackmagic Design Fusion.

Does slimRAW modify or overwrite the original files?

Output files are saved in a location specified by the user. slimRAW does not overwrite, nor modify any input files unless explicitly instructed and confirmed to do so by the user. We do not recommend overwriting originals during processing. You can delete them at your discretion once you are sure the compressed output is correctly stored.

How reliable is slimRAW file output?

About as reliable as copying files can be. RAM errors, storage device errors, OS errors, unexpected power-offs, etc. can all affect writing output data.

So what about checksums?

Checksums help track the integrity of slimRAW generated output, but they can’t help if there is an error in the original file in the first place. Nor do they guarantee data integrity through the production pipeline and into archiving. Checksums do not prevent errors in data, they only help find errors.

What checksum does slimRAW use?

slimRAW uses CRC-32C checksums. They provide very good error detection and are extremely fast to calculate on Apple Silicon and x86 CPUs with the SSE4.2 instruction set, but also pretty fast on earlier x86 CPUs.

I am using a Mac and lossily compressed CinemaDNG frames appear black in Finder/Preview?

Finder/Preview only understands and displays losslessly compressed DNG. The lossily compressed files will still work fine in supported video production software.

Can I compress DNG stills with slimRAW?

Yes. See the user guide for details.