RAW, in depth
A RAW image viewer that opens the folder, not a catalog
Written for Skera 1.0.0 · macOS, Windows and Linux
Nearly every application that can open a camera RAW file wants something in return: import the shoot, let it build a catalog, and work inside its library from then on. That is a reasonable trade when you are editing. It is a bad one when all you want is to look at what you shot.
Why a viewer and not a manager
A photo manager owns your library. It copies or references your files into a database, generates previews on import, and becomes the only place the collection makes sense. The cost is paid up front, before you have seen a single frame — and it is paid again every time you point it at a folder it has not indexed.
Skera has no library, no catalog and no import step. It points at a directory, sorts it the way a file browser would — naturally, so img2 comes before img10 — and starts decoding. It can adjust White Balance, Tone, Presence and Color too, but every edit is a live preview only: the files on disk stay exactly as your camera left them until you explicitly choose Save or Save a Copy.
Which formats open
Standard formats — JPEG, PNG, WebP, BMP, TIFF, GIF — decode through Qt on every platform. RAW goes through libvips, which delegates to libraw, and covers 16 formats across 10 manufacturers:
- Nikon
- NEF, NRW
- Canon
- CR2, CR3, CRW
- Sony
- ARW, SRF, SR2
- Fujifilm
- RAF
- Olympus
- ORF
- Panasonic
- RW2
- Pentax
- PEF
- Adobe
- DNG
- Sigma
- X3F
- Hasselblad
- 3FR, FFF
RAW support by platform
This is the part most download pages leave vague, so plainly: the version 1.0.0 Windows build is compiled without libvips and therefore has no RAW decoder. It opens every standard format and reads the full EXIF record, and a RAW file simply reports as unsupported. macOS and Linux ship the decoder.
- macOS
- RAW + EXIF
- Windows
- standard formats + EXIF, no RAW
- Linux
- RAW + EXIF
Why RAW opens like a thumbnail, and when it doesn't
A camera writes its own rendered preview into every RAW file it saves — the image the camera's own screen showed you. Skera reads that preview directly for on-screen viewing instead of demosaicing the sensor's raw mosaic, so a RAW file opens close to instantly, the first time and every time. The trade-off is honest, not hidden: that preview is whatever resolution the camera embedded, which can look softer than a full decode if you zoom in hard.
Demosaicing — reconstructing a full colour image from the sensor's mosaic — is still genuinely expensive, and still costs roughly one to two seconds. That cost hasn't gone away; it has moved to where it belongs. Save and Save a Copy always perform a real, full-resolution demosaic, because an exported file has to come from the actual sensor data, not a preview. You pay it once, when you export, not every time you look.
Everything else about the cache still applies once an image is decoded either way: an LRU budget of 768 MB of actual resident pixels rather than a file count, decoding in a priority thread pool so the frame you asked for outranks ones being read ahead, and neighbours decoded before you reach them.
Everything from the keyboard
Questions
Does Skera open camera RAW files?
Yes, on macOS and Linux, and with no import step or catalog — you open the folder and the RAW files are simply in it. Sixteen RAW formats are recognised: Nikon NEF and NRW, Canon CR2, CR3 and CRW, Sony ARW, SRF and SR2, Fujifilm RAF, Olympus ORF, Panasonic RW2, Pentax PEF, Adobe DNG, Sigma X3F, and Hasselblad 3FR and FFF. The Windows build ships without the libvips/libraw decoder, so it opens JPEG, PNG, WebP, BMP, TIFF and GIF and reads full EXIF, but not RAW.
How is this different from a photo manager like Lightroom or Apple Photos?
A photo manager wants to own your library: it imports your files, builds a catalog and database, and asks you to work inside it. Skera has no library, no catalog and no import — it points at a folder on disk and moves through it. It can adjust and save a photo (White Balance, Tone, Presence, an eight-channel HSL panel, rotation), but every edit is only a live preview until you choose Save or Save a Copy — nothing on disk changes on its own. It is a tool for looking at photographs quickly and making a handful of adjustments, not a catalog to work inside.
Is RAW slow to open in Skera?
Viewing one is not: Skera reads the preview image your camera already embedded in the RAW file, rather than reconstructing the image from the sensor's raw mosaic, so it opens close to instantly. Only Save and Save a Copy trigger a genuine full demosaic — an export has to be built from the real sensor data — which is where the one-to-two-second cost still shows up, paid once when you actually export a file rather than every time you look at one.
Does Skera send anything over the network?
No. There is no account, no sign-in, no analytics and no telemetry. Your photographs, their filenames, and their EXIF — including any GPS coordinates your camera embedded — are read locally to display them and never transmitted. The only network request is one you start yourself, such as opening a link to this site or to the releases page.
Can I compare two images side by side?
That is what compare mode is for. Press C and the current image is pinned as A with the next one beside it as B; click any thumbnail in the filmstrip to change B. Zoom and pan are linked across both panes, so the two images move together, and both are pinned in the cache so neither is evicted mid-comparison.
Is Skera free, and is it open source?
It is free, with no paid tier and nothing to sign up for. The application's source is private; the binaries are published as public GitHub releases, which is what the download buttons here point at.
Why does macOS say Skera is from an unidentified developer?
The disk image is not yet codesigned or notarized, which requires a paid Apple Developer account. Gatekeeper shows that warning for any unsigned app. To open it the first time, drag Skera to Applications, then right-click it and choose Open rather than double-clicking, and confirm. After that it opens normally.
What does Skera run on?
macOS on both Apple Silicon and Intel, Windows 64-bit, and Linux as a portable AppImage built against glibc 2.31, so it runs on Ubuntu 20.04 and newer, Debian 11+, Fedora 34+ and comparable distributions. It is one Qt 6 and C++ codebase across all three.