Convert top-and-bottom 3D to side-by-side
Some rips, some phone exports and a lot of VR180 footage stack the two eyes vertically. Most headsets and players want them side by side. This page re-packs the image — and works out, from the pixels alone, which half is the left eye.
How it decides which half is the left eye
The two halves of a stereo pair are the same scene seen from two viewpoints, offset horizontally. For anything closer than the screen, the left-eye picture draws it further to the right — so the direction of that offset identifies the eyes.
The tool measures it directly: both halves are converted to greyscale and matched against each other over a range of horizontal shifts, and the shift with the smallest pixel difference wins. It then reports three things — the offset in pixels, how much better that offset matched than no offset at all (the confidence), and which half it assigned to which eye.
- High confidence (over 25%) — the assignment is almost always right; the pair has real parallax and a clear near/far structure.
- Low confidence (under 5%) — the scene has little depth, sits entirely behind the screen, or the halves are already identical. The tool falls back to the usual convention (top = left) and says so. Press Swap eyes if the result looks inside-out.
This is a measurement, not a guess, but it is not magic: a frame where everything is at the same depth carries no direction information at all, and no tool can recover it from that single frame.
What it does to the pixels
Nothing but a re-pack. The top half is drawn to the left slot and the bottom half to the right (or the other way round, when the measurement or your swap says so), at full resolution, then saved as a PNG. There is no scaling, no re-encoding and no re-compression of the picture, so the result is bit-for-bit the same pixels as the source halves — only their arrangement changes. A thin divider is drawn in the preview only; the downloaded file keeps the two halves clean.
Limits, stated plainly
- Images only. For video, the same layout change is per-frame work — convert the clip instead, or re-mux it with ffmpeg.
- Exactly half and half. The split is taken at 50% of the height. A file with letterbox bars baked in will keep them, which is correct, but a file cropped unevenly will come out offset.
- No vertical alignment correction. If the two halves are also misaligned up and down, that stays as it is.
- Half-TB stays half-TB. This changes the arrangement, not the resolution per eye.
Why would a file be top-and-bottom in the first place?
Top-and-bottom (also called over-under, or OU) is the other packing a stereo pair can use: the left eye on top, the right below. 3D Blu-ray rips and some VR180 exports use it; most headsets expect side-by-side instead. The layout that a file uses is not written into the picture, so a player has to be told — and when it is told wrong, you get two shrunken views instead of one 3D image.
What if the output looks inside-out?
Press Swap eyes. Converting a pair to the wrong arrangement shows depth reversed — near things recede. It is a one-click fix and does not re-run any measurement.
Can I check the result before downloading?
Yes — the preview above is the exact image you will get. Viewed with free-viewing (or in a headset) it should read with the subject in front of the background. If it reads backwards, swap.
Related: About DepthSnap · Play SBS/TAB files in the browser · SBS vs top-bottom, explained · Fix the 3D flag in an mp4 · All tools
DepthSnap — free browser-based 2D to 3D SBS converter. No upload, no signup, no watermark.