Compressing RAW files with Rawsie | Hands-on Review

There are only a few options for compressing RAW image files. Rawsie is a new app that uses sophisticated algorithms to drastically reduce the size of those thousands of RAW files taking up space on your hard drives.

Rawsie Main Interface
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There are many ways to compress and optimize JPGs; I’ve covered some of them before. There are far fewer ways to compress RAW files, which can be among the files with the largest filesize in your workflow. A handful of large RAW files isn’t a problem. But when you get thousands, tens of thousands, or hundreds of thousands of RAW files, that takes up a lot of storage space. That means more hard drives, more cloud storage fees, and slower backups.

That there are few apps to compress RAW files is not just some oversight. There are very good reasons not to mess with RAW files. They’re the digital negative, after all, and once you delete image information from the file, there’s no magic way to restore it.

There might be few of them, but there are some options for reducing the filesize of RAW files. Some of them use lossy compression, and some use lossless compression.

Higher-end cameras often give you the option of using a compressed RAW format.1 So that’s one obvious way of compressing your RAW files to save space, but it has to be set before you take the shot; you can’t run existing images through that process.

Until recently, the best way to compress RAW files after the fact has been to use Adobe’s free DNG converter. And it’s still a great option. It works well. It’s reliable. It integrates nicely with Lightroom and Photo Mechanic. And it’s free.

But there’s a new alternative that I’ve been trying out lately: Rawsie. It’s an app specifically dedicated to compressing RAW files. For now, it’s Mac-only, but you can sign onto the Windows waitlist here.

This app is an outgrowth of academic research into RAW image format compression algorithms–it’s not just some random software put together by an app mill. I’ll say upfront that the math under the hood goes way over my head. So I’m relying on what the Rawsie engineers say about what’s happening. But what I’m most interested in–and what I’m focusing on here–are the practical results and where it might fit in my workflow.

Specifically, I’m interested to see whether it saves enough file space to make a real difference, whether the quality remains high enough, and whether the app’s workflow is a good fit for my broader workflow.

Practical Test

For this test, I ran 500 Nikon NEF files through it. A third of them were images from a Nikon D850, a third from a Nikon D810, and a third from a Nikon D800. I tried to include a mix of scenes with a variety of tones and detail. They were uncompressed 14-bit RAW files with the camera’s RAW compression turned off. The individual files ranged from around 40 MB (from the D800) up to around 90 MB (from the D850). The pre-optimized, original versions of all 500 files totaled 35.6 GB.

When running the conversion through Rawsie, I turned on the option to add full-size previews for PhotoMechanic, which will add a megabyte or two to each file. You’ll also get an estimate for the filespace saved, but the results might vary from that. The advantage is that it speeds up previewing the files.

Once you start the conversion process, it takes a while. Just how long is obviously going to depend on how many files, their types, and your computer.

The resulting files totaled 9.2 GB. So it reduced the total collection by 26.4 GB (down from 35.6 GB). Which is a pretty dramatic reduction.

By way of comparison, I ran the same set of files through DNG Converter (the standalone app). I set the JPG preview option to full size and turned the embed fast-load data on, to be a better apples-to-apples comparison. Lossy compression was enabled with the preserve pixel count option. Compatible was set to Camera RAW 12.4 and later. The resulting files totaled 9.7 GB.

In other words, while Rawsie resulted in smaller files overall, there really wasn’t much in it. And not every file was smaller. It’s not like Rawsie is just using a tweaked version of DNG Convertor. The algorithms are different, and the results are going to vary from file to file. On a few files, the DNG Converter result was smaller. But overall, Rawsie led to smaller files more often.

Which means that image quality is the determining factor. There’s no point in me embedding visual images here to show the results–that would just be rendered and compressed JPGs (or WebP, depending on your browser) and wouldn’t be a useful exercise.

So here are a few original, full files to download and compare side-by-side at full resolution on your own screen, if you’re so inclined.

Original Rawsie Optimized DNG Converter Optimized
D850 Sample 1 Sample 1 Sample 1
Sample 2 Sample 2 Sample 2
Sample 3 Sample 3 Sample 3
Sample 4 Sample 4 Sample 4
Sample 5 Sample 5 Sample 5
D810 Sample 1 Sample 1 Sample 1
Sample 2 Sample 2 Sample 2
Sample 3 Sample 3 Sample 3
Sample 4 Sample 4 Sample 4
Sample 5 Sample 5 Sample 5
D800 Sample 1 Sample 1 Sample 1
Sample 2 Sample 2 Sample 2
Sample 3 Sample 3 Sample 3
Sample 4 Sample 4 Sample 4
Sample 5 Sample 5 Sample 5


It’s important to know that Rawsie doesn’t work with all RAW files. There’s a specific list of cameras and RAW filetypes that are compatible with it. And even then, there are some specific limitations depending on the settings used. So it’s very important to first check that your RAW files are compatible.

Input Compatibility. It’s important to point out that Rawsie doesn’t work with every RAW format from every camera. In part, that’s because of the way that RAW formats have developed.2 There are a lot of proprietary RAW formats out there, and they’re not all equal. Back in the days when RAW formats were young and it appeared that RAW formats were going to multiply and become increasingly proprietary and undocumented, there were efforts to open up RAW standards to universal compatibility and transparency. They’re your images, after all, and you should be guaranteed of being able to see and use them 20 years from now without the risk that some camera manufacturer might lock off parts of the metadata or the file format becoming incompatible. Some of the more notable efforts are no more.

At around the same time, Adobe launched its open DNG RAW format. There are legitimate debates about how truly open DNG is–especially when it’s controlled by a commercial imaging company–but DNG is currently the closest thing we have to an open RAW standard in wide use.3

Some RAW formats use proprietary metadata fields that affect the processing instructions. Some use proprietary compression algorithms, such as Canon’s new CRAW (Compact RAW) format. The practical effect of that is that you can’t just assume that you can throw any RAW file at Rawsie and have it work its magic. Some of those RAW formats might already have lossy compression applied. And some simply might be incompatible. So it’s crucial that you check Rawsie’s compatibility chart beforehand. It’s not absolutely comprehensive–I found the Canon R5 files worked well in it even though it wasn’t listed, for example4–but other formats like NEF files from a D3500 were simply excluded because they’re not compatible. (For my testing, I have been mostly using Nikon D850, D810, and D800 RAW files because I have a lot of them easily at hand.) That said, you won’t break anything if you throw non-compatible RAW files at it–they’ll just be ignored, so it won’t corrupt the files.

In addition to the type of camera, there are quite a few specific requirements for the files that Rawsie can optimize. For example, some of the more important compatibility limitations are:

  • Fuji. Not supporting files with “Dynamic Range” setting switched to other than 100%.
  • Canon. Not supporting files with sRAW / MRAW setting switched on (lossy compression).
  • Nikon. Not supporting lossy-compressed settings, i.e., “Lossy Compression,” “Small” RAW size, and “Nikon Compressed NEF.”

Rawsie also doesn’t support very high ISO images in many cases. You can find more on specific camera models here.

So Rawsie won’t work with every RAW file from every camera with every combination of settings. All of which points to the importance of testing out the trial version on your images first.

Output Compatibility. Also, it’s worth mentioning in terms of compatibility of the output, that Rawsie does not save optimized files as a new RAW format. They’re saved in the DNG format, which is the most widely compatible and standardized RAW image format and used by multiple major camera makers and software developers.

Lightroom Catalogs

One of the options for selecting images to process is via a Lightroom catalog. This has a lot of potential. After all, if you’re processing images that are already in Lightroom and converting them from your camera’s RAW format, say NEF or CR2, it will convert them to a DNG. Without intervention, Lightroom won’t know that .dng should replace the .nef in its catalog.

To overcome that rather big problem, Rawsie has a function that can replace the existing reference in the catalog with the new file. And, crucially, the new file inherits the same develop settings and metadata of the original, so you’re not back to square one.

Recognizing that Rawsie is a young app under active development, there are two weak points in the Lightroom catalog side of it that are worth mentioning. (It’s quite possible–and I hope–these might be addressed in a future version of Rawsie.)

Selecting Which Folders and Files to Process. Rawsie can peer into a Lightroom .lrcat file to find the folder listing. And that’s what you use to select which photos in the catalog to process. Which is a very useful feature . . . potentially.

UPDATE: In May 2021 (version 0.9.92), a new feature was added to Rawsie that lets you sort Lightroom catalog folders in the import list, which addresses this issue.

Rawsie Processing Lightroom Catalog Folders

The catch is that the feature isn’t fully fleshed out (at least, not yet). It comes up as a jumbled list of folders without any way to sort them or search them. They’re not listing chronologically or alphabetically. If there’s a rhyme or reason to the listing order, I can’t see what it is. And if you have hundreds or even thousands of folders, that’s very unwieldy. It’s made even more confusing in that there’s no way to know in the list which folders you’ve already processed and which you haven’t.

Here’s an example of what I mean:

Rawsie Processing Lightroom Catalog

Stacked Images. One neat feature is that in processing the images using Rawsie’s Lightroom interface, the newly generated DNG versions are automatically relinked in Lightroom, replacing the originals. So you should be able to go right back into Lightroom and continue working just as normal, without having to re-import the new versions. In my experience, the updated files in the Lightroom catalog have been successfully inheriting the develop and metadata information.

With one important exception: stacking status. This becomes an issue when you’re using derivative versions. And, unfortunately, I tend to use stacks quite a lot in my workflow. As an example, I often process images in DXO Nik Color Efex or Silver Efex. That generates a TIFF file that sits stacked on top of the original. And I know that that is the best version and the one I want to be using for exporting, sharing, or printing. That’s the version I use in my publish collections, smart folders, and the versions that have keywords and other metadata updated. But when you reprocess the underlying RAW file in Rawsie, the new, processed version is no longer stacked with the TIFF, essentially orphaning the TIFF. Which leads to more clutter and confusion. This isn’t going to be an issue for everyone, but it’s a rather large issue for me.

Compression of an Archive

This is the most logical use of Rawsie in its current incarnation: to compress an archive of existing images. Because the chances are that you’ve accumulated a large archive of images that are taking up space. You don’t want to delete the RAW files just in case, but you probably also don’t need them to be full-blown uncompressed RAW files.

This is also the most logical option to use when you’re converting new images at the start of your workflow.

Using this is straightforward. You can either drag and drop the images from Finder onto the drop panel or use the Browse button.

Rawsie Process Individual Images

Compression on Ingest

I’m focusing mainly here on compressing archival images. That is, RAW files that have been accumulating on my hard drives from previous shoots.

But another logical place in a workflow to insert the compression step is when first ingesting new images. And doing this would avoid some of the Lightroom integration issues I describe above.

The logical option to use for this kind of workflow is the “Optimize individual raw files” option. Don’t be put off by the “individual” there; you don’t have to do them one-by-one. You can process batches of images or folders at once. It’d be especially useful for photographers that routinely come back with a large number of images from a shoot–things like wedding photographers or sports shooters.

This is an area where DNG Converter has a distinct advantage, because it’s built right into Lightroom’s ingest function. There, you can choose the Copy as DNG option to convert and, with appropriate settings, convert the RAW files as a single process (or, at least, an automated one). So the advantage that DNG Converter enjoys is that it’s a one-step process. With Rawsie, you’ll need to copy the files to your hard drive, wait for them to finish copying, convert them with Rawsie, wait for it to finish, and then import them into Lightroom or another image browser/editor. DNG Converter isn’t necessarily any faster at any of these steps, but in combining them in one single, chained process, it is much more convenient.

Things Worth Knowing

You’ll need a recent version of Adobe DNG Converter installed alongside Rawsie. It’s not clear to me how exactly Rawsie is using it behind the scenes, but you’ll get a warning message if you don’t have a recent version installed. You might also get prompted to update Adobe DNG Converter when you try to install some Rawsie updates.

Rawsie DNG Converter

When using the “Optimize Lightroom catalog folders” tool, Lightroom can’t be open.

Wrap Up

As I said upfront, I’m interested primarily in two things: the practical results and where it might fit in my workflow.

I can’t quibble with the results. The files are drastically smaller, and if there’s any real drop in quality, I’ve been unable to spot it. And the files remain fully editable and compatible. So this box seems easily checked.

The workflow part is trickier. Simply put, I’m having a hard time finding a place for it my workflow–at least, not one that keeps things efficient and doesn’t add a few extra steps. Of course, everyone’s workflow is different. In my case, the complication is that while I use Lightroom as my workflow hub, I routinely process some images with external editors such as Photoshop or Nik Collection or Silver Efex or FilmPack. And in those cases, it saves a new version as a TIFF file and separates the master file and the derivative versions, making it hard to keep track of what’s what.

But Rawsie is a young app, and there’s plenty of opportunity for growth and refinement moving forward. I’ll be watching with much interest.

  1. What options you have here varies from camera to camera. Some cameras only use lossy compressed RAW files. Some give you the option of using either uncompressed or compressed RAW files. And some offer the option of choosing what kind of compression to use. Newer Canon cameras even give you the option of what kind of RAW format. 
  2. There are other reasons: compressing an already-compressed RAW file doesn’t make much sense, and some cameras–notably from Fujifilm–use a unique sensor type that works differently than other digital image sensors. 
  3. When converting to DNG, you also have the option of embedding the original RAW image in the file. Doing that won’t do you any favors if you’re trying to minimize file size, but it will ensure maximum compatibility in the future. 
  4. R5 compatibility has since been officially added with version 0.9.89 on January 27, 2021
David Coleman / Photographer
by David Coleman

I'm a professional freelance travel photographer based in Washington DC. Seven continents, up mountains, underwater, and a bunch of places in between. My images have appeared in numerous publications, and you can check out some of my travel photography here. More »

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