Photo measure

How to measure something in a photo

It's simple to determine distances on maps or technical drawings such as architectural (floor) plans when you have its scale and a ruler.
Because everything is in a single plane, measurements can be taken directly. The real-world dimensions are then obtained by simply applying the scale.
Photos on the other hand are a two-dimensional projection (image) of the three-dimensional world (object).
As a result, objects appear smaller with increasing distance — that's called perspective.
Without additional information, it cannot be determined whether it is a small object nearby or a large one far away (depth perception is more difficult with one eye closed).
Consequently, to determine the size of an object from a single image, a reference object for scale needs to be in the same image plane, i.e. close-by and at the same distance from the camera.
Additionally, camera lenses cause distortions (think fish-eye view).
As a result, expect this method to be useful only for estimates. The accuracy depends very much on the image.
So please don't blame me if e.g. your kitchen furniture don't fit - No Warranty

Detailed instructions

1. or drag&drop an image anywhere onto this page. The picture will be scaled to fit the page width.
2. Expand the editor area for a larger view
3. Rotate the image as needed (Limitation: measurement lines can't be rotated with the image)
4. Create the reference dimension (red) by click-and-dragging the first measurement line onto an object with known size.
5. Enter the real-world length of the first dimension as reference - the other measurements will be scaled accordingly.
6. Create measurement lines (green) by click-and-dragging (remove them by clicking on the 'remove' link in the measurement table below).
7. Save the annotated image and the measurement data via the respective buttons or right-click the image and "Save Image As ..."
   (Bug: Saved with the current resolution, not the original. Working on it.. )

Hints

Further tips for using the tool:

• Drag an endpoint to adjust a line
• Hit (or click) DEL to remove the last measurement
• Use the measurements table to remove any measurement
• Press (or click) ESC to abort drawing the current line or clear all measurements. Hit it twice within 1 second to clear the image.
• Hold (or click to toggle) CTRL while dragging to "snap" horizontal/vertical lines
• You can enter a unit in the scale, it'll show up in the results (it does not affect the measurements).
• Leave the scale empty if you want to measure pixels (pixel measurements will be off for scaled images).