User Guide


On Microsoft Windows: Double-click the downloaded setup executable and follow the instructions in the setup wizard.

On Apple macOS: Double-click the downloaded .dmg file to mount and open it. After accepting the License Agreement you will be presented with the following window:

Drag the icon to the Applications shortcut to install the slimRAW application bundle on the system. If you already have an older version of slimRAW installed select Replace to overwrite the older version when prompted by the OS. You can then start slimRAW by double-clicking its icon in the Applications folder.


You will need to enter your license key to unlock the application. This can be done by going to the File menu, and selecting Register.

Controls and operation

Tip: Most UI controls will display tooltips with a short explanation of the control's function when you roll your mouse over them.

The following screenshots use the Windows version for illustration but the macOS version has the same controls organized in the same layout. Here is an overview of the controls:

Use the Choose Folder... buttons to select the folder containing source footage and one or two folders to save the output into. slimRAW can output to two locations simultaneously. You will need to select the Enable second output checkbox for this. If you select the same folder for input and output slimRAW will ask for confirmation as this will overwrite the original files during processing. Exercise common sense with this feature. It might not be wise to overwrite important video data. You can always delete originals at a later time.

Use the Compression mode radio buttons to select the type of compression performed by slimRAW. There is a choice of lossless and lossy compression modes. Read more about them here. Note that while losslessly compressed CinemaDNG is widely supported by video production applications, lossy compression support is more limited. Check the FAQ for a detailed list of compatible software.

If one of the lossy compression modes is selected, a Prioritize quality over rate checkbox is enabled. If it is ticked, slimRAW will take extra care of output image quality even if this would mean that the target compression ratio cannot be met.

Check the Premiere CC compatibility option to have slimRAW create losslessly compressed CinemaDNG files compatible with Adobe Premiere Pro CC and Adobe SpeedGrade CC. As of November 2016 support for losslessly compressed CinemaDNG is incomplete in Adobe Premiere Pro CC and Adobe SpeedGrade CC. Checking this option ensures the compressed output from slimRAW is compatible with these two applications but will trade off a little bit of compression. This does not concern Adobe products using Adobe Camera Raw to import CinemaDNG footage (Adobe After Effects, Adobe Photoshop and Adobe Lightroom). If you don't plan to import the losslessly compressed raw video in Adobe Premiere Pro CC or Adobe SpeedGrade CC you can leave this option unchecked. It is possible that Adobe might expand support to the full CinemaDNG specification in the future, in which case files created without selecting this option might work with future editions of Adobe CC.

Use the Downscale 2X option to produce CinemaDNG output at half the original resolution. For example, this option will produce 2K CinemaDNG from 4K CinemaDNG, 2.3K from 4.6K and so on. The main intent of this functionality is generating raw proxies (more on CinemaDNG raw proxies here). But it can also be used for reducing the excessive resolution of timelapse material and for the general reduction of high resolution footage to more manageable sizes when planning deliveries at 1080p/2K. Using this option can lead to tremendous disk space gains, as well as largely reduced CPU and GPU power requirements in post production while preserving a fully raw workflow, but at the obvious expense of resolution. This is a Bayer mosaic to Bayer mosaic downscale so aliasing/moire can be introduced in fine patterns.

Check the Process subfolders checkbox to enable recursive processing of any subfolders in the selected input folder. The folder tree structure will be recreated at the output folder. In most cases you will probably want to leave this option selected.

Select the Copy non-DNG files option to have slimRAW copy any non-DNG files in the input folder(s), like audio or external metadata files, to the output location. This option also enables slimRAW to serve as a general purpose copy/offload utility which can be used to copy any data with checksums generation and verification (see below for checksums functionality), and not just DNG/CinemaDNG raw files.

Use the Existing files policy radio buttons to set how slimRAW should handle any source filenames already existing at the output location. Such files can be skipped or overwritten. This setting is irrelevant when slimRAW is outputting in an empty folder.

When the Generate checksums option is selected slimRAW will calculate and save checksums for every DNG file it outputs. If the Copy non-DNG files option above is selected slimRAW will also calculated and save checksums for the non-DNG files it is copying to the output. Checksum lists are stored in a file called in each folder. Checksum generation is pretty fast and it is even faster (almost free) if you have an SSE4.2 capable CPU.

When Generate checksums is checked the Run a verification pass checkbox is enabled for user selection. If Run a verification pass is selected, slimRAW will automatically verify output for checksum errors once the compression/copy process is finished. This will ensure output files have been correctly written to the output device.

Use the Start Job button to initiate processing once you've selected the desired settings.

During processing a Pause Job button and an Abort Job button are enabled. Since slimRAW may consume a lot of the available CPU resources (as long as the storage system can keep up) the Pause Job button might be useful if you need CPU power and the current job is not finished yet. The Abort Job button is self-explanatory.

A few more options are available in the Other options dialog accessible from the File menu. The Maximum compression option ensures that slimRAW will produce the smallest possible files. The default compression profiles of slimRAW are already pretty good so usually savings are marginal. The downside of this setting is that slimRAW will run a bit slower (approx. 1.5X longer processing). On the other hand, if your processing is storage bandwidth limited enabling Maximum compression may not result in longer work times.

Conversly, the Fastest option ensures the fastest processing possible at the expense of some compression. It might be useful when compressing high resolution video (4K or larger) under time pressure. Again, if your processing is storage bandwidth limited enabling this option may not result in shorter work times. This option also produces losslessly compressed files that Preview/Finder in Apple OS X 10.9 reads correctly. Preview in OS X 10.9 has incomplete support for losslessly compressed CinemaDNG so special handling is needed in slimRAW for files to appear fine in Preview. Note that this only affects appearance in Preview. The compressed files will work fine in video applications even without this option. OS X 10.10 has improved support in Preview/Finder for losslessly compressed CinemaDNG so enabling this option isn't necessary for Preview to display images correctly. Fastest and Maximum compression are mutually exclusive. Note that these two options only affect the lossless compression mode.

By default, slimRAW compresses all uncompressed DNGs and recompresses all compressed DNGs it encounters in the input. Recompressing suboptimally compressed lossless CinemaDNG can reduce size further, sometimes up to 20% with no quality loss whatsoever. And recompressing lossless to lossy will usually yield much more significant size reduction (but will trade off some quality). Check the Don't recompress any compressed input option if you only want to compress uncompressed input files. This will copy any compressed DNG files straight to the output without modification.

Enable the Preserve creation/modification file times option to replicate input file times in the output. Note that file time resolution depends on both the operating system and the file system of the storage devices, so it might be impossible to replicate input file times exactly.

Enable the Sound notification on job done option to have slimRAW play a notification sound when processing finishes.

The Adjust Digital Bolex D16 metadata option can be used to address some black level related issues in D16 raw footage. It will only modify metadata in files sourced from the D16 camera, so it is safe to use in a mixed camera input. This is an utility option and it is unrelated to compression. For best results with D16 CinemaDNG make sure your camera is upgraded to the latest firmware (version 1.5 at the time of this writing).

The Set DNG WhiteLevel to this value option can be used to force a specific white level value for all the output DNG footage. This advanced setting is unrelated to compression. It can be used for fixing miscalibrated (tinted) highlights. See more here.

You can also select a folder where checksum verification logs are written to in case issues are encountered during verification.

During processing progress and elapsed time are displayed for reference. Once processing is finished some statistics are displayed, most notably the achieved compression level. If slimRAW encounters any DNG files it can't handle, they will be copied to the output without modification. Such files include files in any unsupported uncompressed or compressed DNG format and invalid/corrupted DNG files. All of these are being counted under the DNG files copied without compressing tag.

Checksum verification

Next to each of the selected input and output folders is a V button. Use these buttons to verify the content of the corresponding folder against any previously generated checksums. Checksum verification honors the Process subfolders setting so the content of entire folder trees can be verified with a single click of the mouse. Once finished, slimRAW will signal in red text if errors are encountered. Possible errors found include checksum errors, missing files and corrupted checksum lists. If any errors are found, up to 20 issues will be reported in the log text control. If there are more issues, the full error log will be saved in a text file for reference and its location reported in the log control.

Note that Adobe Camera Raw overwrites metadata in DNG files so applications importing and processing CinemaDNG through Adobe Camera Raw will invalidate any checksums generated beforehand.

Checksums can be verified cross-platform in case of a mixed OS production environment: checksum lists created by the Windows version can be verified on macOS, and vice-versa.

Customizing the finished job notification sound

You can customize the sound used for notifying job finish in slimRAW. In Windows, go to Control Panel. Search for Change system sounds. In the program events list set the Asterisk sound to any system supplied or custom sound you like.

In Apple macOS, go to System Preferences -> Sound -> Sound Effects and select an alert sound from the list of available sounds.

Data integrity

ALWAYS shut down the operating system properly after processing if you want to power off the computer. ALWAYS eject and disconnect external storage devices properly, do not simply unplug them. Modern operating systems employ efficient caching algorithms which greatly improve performance when using storage devices, especially when writing out data. If you don't shutdown the OS properly or don't disconnect external storage properly, you risk losing data.

Backup of important data is always a good idea. While data errors are not extremely common, they probably happen more often than you'd expect. A lot of things can go wrong in a computer: RAM errors are not always apparent but may silently lead to corrupted data; storage devices may defect; operating systems may crash; power goes off unexpectedly. And these are just the trivial possibilities.

Checksums will help track the integrity of slimRAW generated output through the production pipeline and into archiving, but they can't help catch any errors in the original input files. Nor do they guarantee data integrity: checksums do not prevent corruption, they only help find corruption. Handling any data errors, should they occur, is easier if you have backup.

Notes on performance

When processing big amounts of data there are three possible performance bottlenecks: input storage bandwidth, CPU power and output storage bandwidth. Outputting to the device which streams the input footage will impede performance, as reading and writing data will compete with each other for bandwidth and in the case of hard drives will also add to drive head movement.

In a lot of cases processing will be limited by the bandwidth of the storage device streaming the input files. Data can only be processed as fast as the input storage device feeds it to slimRAW. Note that for external storage devices bandwidth may be limited by connection specifics. For example, externally connected SSD drives may have a hard time showing their true speed.

Output storage bandwidth will generally be less of an issue. Output files will be compressed, hence less bandwidth needed.

Since slimRAW is optimized for multiple cores and makes good use of available CPU power as long as storage can keep up, CPU processing is likely to be the bottleneck only when storage bandwidth is abundant.

As a conclusion: SSD and/or RAID will probably help performance the most in case of performance hiccups.

slimRAW and DNG raw stills

slimRAW can be used to compress uncompressed DNG raw photos and to optimize size of already losslessly compressed DNG photos. If the Premiere CC compatibility option is selected the output can usually be imported in Adobe Premiere Pro CC and Adobe SpeedGrade CC. This has been tested with DNG photos from cameras like the Pentax 645z or Leica M Typ 240. Note that the metadata of some stills cameras is too complex (or non-standard) for Premiere to handle and it will reject both the original uncompressed and the slimRAW losslessly compressed files. Premiere may also reject vertical stills. slimRAW can also be used to get non-DNG raw photos into Premiere/SpeedGrade but the files will need to be converted from their native raw format to DNG before being passed through slimRAW.

Note that when (re)compressing DNG stills slimRAW will remove any thumbnails and preview images embedded into the original DNG file. This is needed for compatibility with some video apps but also helps reduce filesize a bit.

Support for DNG stills is currently experimental since we can't test all possible sources of DNG stills. Use the trial to test with files from your particular camera model if you are considering slimRAW for this feature alone.

Miscellaneous notes
  • The Ikonoskop Audio Tool, used for extracting audio from the Ikonoskop DNG files, won't work if there are any non-DNG files in the DNG sequence folders. In particular, it won't work if the folders contain checksum files.
  • Importing footage through Adobe Camera Raw invalidates previously generated checksums because ACR modifies metadata inside the files.
  • When importing in Adobe Premiere Pro drag the first frame of the sequence in the media pane. If footage is imported as a folder Premiere will choke on the checksum file (if checksums have been generated). Importing folders is also significantly slower in general because Premiere attempts to load the whole folder immediately.
  • Don't bother with the Premiere CC compatibility option if you are not using Premiere. Note that footage can always be reprocessed with this option enabled if the need arises at a later time.