problem : warp transform auto proportions

[pierrelabreche]

Auto computation of proportions is off.

Example :
I took a picture of a photo in a museum.
The actual proportions of the photo are 1,382 : 1.
I computed the proportions from another picture provided by the museum.

When corrected automatically using Warp, PWP computes proportions as 1,561 : 1

2024-11-15 PWP Warp auto v1-resize.jpg (119.92 KiB) Viewed 1844 times

To obtain the desired correction, user has to use custom proportions.

2024-11-15 PWP Warp custom.jpg (120 KiB) Viewed 1844 times

[jsachs]

Auto-proportions just makes a guess that assumes the middle of the frame is correctly proportioned. This usually works OK if you photograph something head on, but not from the side.

[pierrelabreche]

The perspective computation could be improved. I compared with DxO Photolab 8.

Photolab automatically computes 1.5, which is much closer to reality.

2024-11-15 DxO Photolab 8 Warp auto.jpg (75.85 KiB) Viewed 1837 times

[jsachs]

Yes, you can do a better correction but only if you know the focal length of the lens and the size of the sensor and do a lot of complicated geometry. The approximation in Warp does a good job on images landscapes and other images if you point the camera up or down a little which is the most common case. Otherwise you can set the proportions manually.

[pierrelabreche]

Thanks, it is good to know those limitations. I was relying too much on Warp for auto proportions.

[pierrelabreche]

Thank you for your analysis.

The aspect ratio could be computed based on the image desired verticals and horizontals, which could be identified by the user or auto-detected by AI analysis of the image. More importantly, the aspect ratio could be computed automatically based on the sensor and optics EXIF or other metadata. If the optics is not built-in the EXIF, the 35-mm equivalent or the exact focal length and sensor size could be asked from the user.