How the frames get lined up with each other.

No Alignment - Tripod

Uses the frames exactly as shot. Right for a solid tripod, for in-camera multiple exposures, and any time you want the frames left alone.

Auto Align - Use All Frames

Lines the frames up and keeps every one. The safe choice for handheld work and for a tripod that got bumped. If the frames were already aligned it detects that and skips the work.

Night Align - Smart Frame Selection

For handheld bursts in low light. As well as aligning, it decides which frames belong in the merge: blurry ones go, ones it cannot line up confidently go, and it favours the stretch of the burst where your hands were steadiest.

Expect it to use fewer photos than you selected. That is the design, not a fault. Shoot twenty or thirty frames so it has something to choose from.

Needs frames of matching exposure. For a bracket, use Auto Align.

Not the mode for light trails. Frame selection is looking for a sharp handheld frame, and a tripod stack of traffic or city lights is not that, so it will throw most of your frames away. Use No Alignment with Lighten instead.

Align Stars - Sky Tracking

For untracked night sky exposures. Aligns on the stars rather than the ground, giving pinpoint stars with the noise reduction of the whole stack. Satellite and aircraft trails are removed automatically, and frames where cloud hid the stars are still used.

Pixel Shift

For sequences shot in your camera's pixel shift or high resolution mode. Gives real measured colour at every pixel, and on the half-pixel modes, extra resolution. Nikon, Sony, Canon, Pentax and Fujifilm.

Select the whole sequence and nothing else. It has to be 4, 8, 16 or 32 frames, or 20 for Fujifilm X-Trans. If a frame got bumped, MergeRAW says so rather than dropping it, since the set has to stay complete.

Merge Raw Files (Advanced) adds batch processing and sensor cleanup alongside the same two columns. All of it is optional, and the defaults match the simple dialog. Pixel Shift greys out Hot Pixel Removal and Demosaic Mode, because it assembles the raw frames directly.

Batch Mode

Hand it a whole shoot and get one file per group instead of one file total.

• Merge All Photos combines the selection into one DNG. The default.
• Merge Each Stack runs one merge per Lightroom stack. Stack as you cull, then merge the lot in one go. It pairs well with Lightroom's own Photo › Stacking › Auto-Stack by Capture Time, which groups a whole card of bursts for you in one step.
• Merge Each Directory does the same by folder.
• Process Each Photo does not merge. It applies your corrections to each photo separately, one DNG each. This is how you dark-frame or flat-field a whole shoot.

Hot Pixel Removal

Finds and repairs stuck pixels without needing a dark frame. The choice exists because a hot pixel and a star look the same to software, so you are telling it what it is looking at.

• Automatic reads each frame's exposure time and overall brightness to work out which of the two policies below fits, and leaves short exposures alone entirely. The default, and right for nearly everything.
• Night Sky is deliberately cautious, because eating real stars is worse than leaving a speck.
• Daylight Long Exposure can be more aggressive, since nothing in frame should be a lone bright dot.
• Off disables it.

Dark Frame(s)

A shot with the lens cap on, at the same exposure and temperature as your photos. It shows exactly which pixels misbehave, so those get repaired and nothing else is touched. More thorough than Hot Pixel Removal above, and worth it for long exposure and astro work.

Flat Field Frame(s)

A shot of an evenly lit blank surface, taken with the same lens and aperture. It corrects vignetting and corner colour shift, the broad smooth unevenness across the frame rather than small spots. Mostly matters for copy and reproduction work, where flat areas need to actually be flat.

Give it flats from several apertures and each merge uses the ones matching its own f-stop, with a nearest-aperture fallback. Still experimental, so check the corners of anything important.

Picking Calibration Frames

Both pickers offer two families. Filter by Filename, Directory, Colour or Stars pulls frames out of the selection you already made, so labelling your darks on import is enough. File on Disk and Directory on Disk reach anywhere on your drive, catalog or not, and remember where you have been.

Several matching frames get averaged into one cleaner calibration frame automatically, so pointing at a folder of twenty darks beats picking one.

Frames picked from disk that are not already in your catalog have to be added to it, and MergeRAW asks first. Lightroom gives plugins no way to remove them afterwards, so they stay.

Demosaic Mode

Raw files record one colour per pixel and something has to fill in the rest. Normally that is Lightroom's job, and leaving it there keeps the most flexibility, but some merges have to do it themselves first.

• Auto does as little as possible: a normal raw file when the merge allows it, the best method for your sensor when it does not. The default, and almost always right.
• Sharper always uses MergeRAW's own conversion, which resolves finer detail on some sensors. Because it always converts, you can point it at a single photo and use MergeRAW as an alternative raw converter.
• Safe hands that step to Adobe DNG Converter. Try it if a merge shows colour artefacts you do not like. Needs the converter installed, and is slower.

• Remove Built-In Profile strips the mandatory lens corrections some cameras bake into their raw files.
• Edit Raw in Photoshop round-trips through Photoshop and comes back as a raw file you can still develop.
• Fix IR PDAF Banding removes row banding from infrared and full-spectrum conversions.

What changed in the latest version is in the change log.