PTGui tips and tricks
Tuesday, September 10, 2013
PTGui is the professional choice for panoramic photography creation, and our favorite tool to create calibrations for VideoStitch. It shines with its convenient user interface that allows easy editing of control points and tweaking of all optimization parameters.
This article points out some tips that are usefull when creating camera array calibrations for VideoStitch.
Chose carefully which video frames you work with
When extracting images from VideoStitch to work in PTGui, chosing a good frame set is the key to successfull stitching. It should provide enough details in overlapping areas for adding control points. The following images were extracted from the same videostitch project :
The first set was extracted at 00:00:00, the blue sky doesn’t offer any visible detail to add control points between images 1 and 4 :
After seeking a better frame and extracting the images from VideoStitch again, we can easily add control points were they were missing :
[tip]When extracting images from VideoStitch to overwritte a previous frame set, PTGui will update automatically.
This allows to easily combine control points from different frames.[/tip]
Generate control points in a specific image area
This is probably the first step if you are getting started with PTGui : adding control points where the images don’t stitch properly, in order to provide PTGui with the informations it needs to adjust images parameters.
PTGui offers multiple options to automatically generate control points : between image pairs, and between all images. These commands are all available in the main window’s “Control Points” menu.
But what if we want to generate control points automatically in a specific area ?
Of course, there is a very convenient way to do this :
- In the control points tab, while holding the “Shift” key down, click & drag your mouse to define a selection.
- Right click on this selection, and chose ‘add control points here’ to generate more control points within this area.
[tip]The selection can also be used to remove multiple control points at once. Just hit your keyboard’s ‘delete’ key.[/tip]
Optimize parameters wisely
By default, PTGui provides a simplified interface to it’s optimizer. But stepping into the advanced settings it is possible to get finer control.
Start, with the default setting, by optimizing globaly lens fov, the lens b distortion parameter, and image yaw, pitch and roll. ( b distortion is refered to as ‘Medium’ lens distortion in the optimizer ‘simple’ interface ).
Optimizing Shift for each image individualy is another trick specific to 360 video rigs. Make sure to check “use individual lens parameters” in the “lens settings” tab enable this feature.
When you have good alignement with ‘Medium’ lens distortion, optimizing ‘heavy’ lens distrotion ( lens a and c parameters) isn’t necessary, but may improve the results but require that your control points are well spread over the entire overlapping areas.
[tip]Disabling yaw, pitch, & roll optimization on one of the images ensures the panorama global orientation is preserved during optimization.[/tip]
Re-initialize your project when optimization fails
If PTGui’s optimizer keeps giving you erroneous results, don’t forget to re-initialize your project. This will get you back on tracks most of the time.
Follow the control points assistant
The “control point assistant” window can help you improve results by giving you suggestions on improving the project.
You can access it anytime by clicking on the control points table button.
Make sure that all overlapping image pairs have control points.
Remove worst control points
Sometimes, a few missplaced control points can introduce optimisation error. Remove these control points can help to achieve a better optimization, and thus better visual output.
PTGui has a dedicated function to remove the worst control points. It can only be used after a first optimization has been done, since the ‘worst control points’ are those that yield the most optimization error.
Control points can also manually be removed directly in the control point lists : the ones that show the most ‘distance’ can usually be considered outliers
To locate and view a control point in the image, just double click on it in the list, it will display and be selected instantly in the control point tab.
Draw straight lines with the mask tool
VideoStitch automatically imports PTGui pro ‘s red masks (it doesn’t take the green mask).
Did you know, it is possible to draw straight lines with the mask tool ?
- Simply chose the pencil to draw red masks, and click where you want the line to start.
- Press and hold the “Shift” key down, and click where you want the line to stop.
Change the “Align Image” behavior in your templates
PTGui pro users can change the “align images” button behavior in the “project settings” tab. These settings are also saved in PTGui templates, so that when this project is applied as a template, it will keep the “align images” button behavior.
Need more tips for your camera array calibrations ?
Our support forum has a section dedicated to PTGui, Hugin and camera array calibration.