What “4K photo” really means
A UHD 4K frame is commonly 3840 × 2160 pixels, roughly 8.3 megapixels. That tells you the image dimensions, not its true sharpness. Video compression, focus and shutter speed all influence detail.
Avoid accidental downscaling
Use an extractor that draws the decoded video at its native videoWidth and videoHeight rather than capturing the scaled on-screen preview. Our extractor is designed to do that, bounded by the device’s browser memory and canvas limits.
How to verify the result
After exporting, inspect the image information on your device. Dimensions around 3840 × 2160 are expected for UHD video, while portrait and cropped videos can differ. Try a JPG if PNG exports are too large.
When 4K is not enough
Motion blur from a slow shutter cannot be repaired simply by exporting more pixels. Recording in brighter light or using better stabilization often improves action photos more than changing export settings.
We have automated verification for 640 × 360 source-resolution output, not exhaustive testing across 4K/8K phone models. JPEG is lossy, while PNG is lossless relative to the browser's decoded image; neither restores details already lost in video compression.
- Check width and height in the source video's properties.
- Export a frame as JPEG and locate the saved file.
- Inspect the exported image dimensions. They should match the decoded orientation and dimensions of the source, not the on-screen preview size.
- Zoom to 100% and examine edges, fine hair, or lettering. Large pixel dimensions don't rule out motion blur or compression artifacts.
What to measure after exporting
A UHD clip contains 3840 × 2160 = 8,294,400 pixels per frame. A 1920 × 1080 file contains 2,073,600 pixels. The UHD frame therefore has four times as many pixels, but only twice the width and height. If a tool draws the video onto a small 640 × 360 preview and exports that canvas, it discards most of the available pixels. Our frame extractor instead uses the decoded videoWidth and videoHeight for the export canvas, provided the device can allocate it.
Worked example: pixel dimensions versus saved quality
Related guides
Check portrait and preview dimensions
A portrait UHD clip may decode to 2160 × 3840. Compare width and height in the extractor’s Export studio with the properties of the saved photo. Zooming the preview does not change the saved dimensions. Try a short local copy if the full clip runs out of memory.