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APP/APG v2.0 Geometry Editing

Correcting Image Geometry

Issues involved :

Two words: framing and perspective. Reframing the panorama is quite easy, there won’t be much involved in this step. Perspective correction in the other hand will require relocation of the horizon at the right place, then choosing the desired projection type: you can let the software manage these steps automatically and you will, most of the time, obtain decent results; but not always...

There are two ways to approach the perspective issues:

  • the trial and error method based on the initial output of Autopano Pro displayed in the Panorama Editor window and choose what you may see fit best.
  • gain an understanding of the mechanics driving the process, what are the available choices and the results you can expect from the different methods.

Autopano Pro is very well suited for the “trial and error” method as it will display almost instantly the results of each change you can make in the geometry variables.

What you must know about perspective is quite simple: if you take a photograph of a tiled floor, the individual tiles naturally line-up on the right perspective path and no trigonometry calculation is necessary to take a picture of a spiral staircase! Since the early stages of photography, comforted by the idea that they did not have to master the perspective concepts, photographers got used to almost ignore the approach to perspective.

For more information on the subject you can read the Understanding Projecting Modes page and learn how Autopano handles these issues.

The Tools

  • Projection: Proj0 mercator.png Proj0 plan.png Proj0 cylindre.png Proj0 sphere.png
  • Image Mode: Layer mode off.png Layer on.png
  • Rotate: Rot180.png Rot90left.png Rot90right.png Yawpitchroll.png
  • Crop: Fit.png Crop.png
  • Point of View: Cross center.png Level.png Vertical1.png

Projection Modes

  • Proj0 mercator.png Mercator Projection
    • Advantages: can handle horizontal FOVs up to 360°. Stretching effect at the top and bottom of the image is reduced compared to the Spherical projection.
    • Downside: all straight lines parallel to the horizon (curbs, building tops) will, to various extends, be bent. The vertical angle is limited, it MUST be smaller than 160° because the stretching effect will start to appear at the top and at the bottom of the image passed 55° from the horizon (over and down).
  • Proj0 plan.png Linear Projection
    • Advantages: always a good choice when working with a small FOV (field of view), recommended for architecture as it is the only projection mode that will not curve any line (the other two modes will always, to a certain extend, “bend” curbs and building tops).
    • Downside: in theory this mode can only be used if the FOV is smaller than 180°, determined by the diagonal of the image. In real world situation the limitation is actually 90° as the stretching produced on both edges of the image is already visible at 90°, and even more pronounced at the corners. Passed 120°, the results become unacceptable as the stretching will produce a significant and uncomfortable loss of sharpness.
  • Proj0 cylindre.png Cylindrical Projection
    • Advantages: can handle horizontal FOVs up to 360°.
    • Downside: all straight lines parallel to the horizon (curbs, building tops) will, to various extends, be bent. The vertical angle is limited, it MUST be smaller than 160°, but a stretching will start to appear at the top and at the bottom of the image passed 45° from the horizon (over and down).
  • Proj0 sphere.png Spherical Projection
    • Advantages: this is the default choice as it can handle any panorama type.
    • Downside: For a direct display on a computer screen (without using a special viewer) or to print the panorama, you must first make sure that the amount of curvature of the lines parallel to the horizon stays acceptable. There is no set rule to determine what is acceptable and what’s not, you must use your best judgment. When the vertical field of view is large, the stretching of the top of the image (close to the zenith) and of the bottom of the image (close to the nadir) can vary from very natural to quite unnatural

The Tools

Layer mode off.png Layer View Mode Layer on.png

The Layer View mode will let you visualize how the original images are arranged in the panorama. Activate the Layer View mode by clicking the button, next run your mouse pointer over the panorama to see the actual photo located under the pointer’s location. If the cursor is on top of an overlap (i.e. stitch seam), use the mouse wheel to scroll through the different pictures overlapping at the current location.

When the mouse pointer is located outside of the panorama area, the whole panorama is shown (i.e. the resulting stitched image with brightness, contrast and colors adjusted on the overlaps).

Another click on the button will exit the Layer View mode.

Icon-tips-24.png Tip:

  • The task bar displays information related to the current selection (i.e. the selected image): number and file name. This is often useful to identify an image we want to exclude from the panorama using the Control Points Editor.


Rotations: 90° Left Rot90left.png, 90° Right Rot90right.png, 180° Rot180.png

These three buttons let you rotate the panorama when the original pictures in the source group have a wrong landscape/portrait orientation. Note that even if the panorama looks well aligned in the first place, a 90° rotation can result in a wrong panorama alignment: it is then good practice to use the Auto Level tool after a rotation.

Actions

  • To cancel an action after it is completed use the History by clicking on the History.png icon.


Yawpitchroll.png Numerical Transformation

Transformation numérique

As surprising as it may sound this tool can by itself perform all the panorama modifications allowed by the following tools.

  • 180° Flip
  • 90° Left rotation
  • 90° Right rotation
  • Set Center Point
  • Auto Level
  • Set Verticals

It is obviously more reasonable to hand a camera to a person who never took pictures than trying to explain to that person what you see in the viewfinder when orienting the camera in different directions!

So, it is probably a better use of your time to stitch the example pictures provided with Autopano Pro and to alter the values (let’s say 10 then -10) of the three different parameters provided for this tool. One word of warning however before you proceed: alter only one parameter at a time and never all three of them at once! Try this first with the Spherical Projection, then with the other projection types.

Note that if you do not spend the time to carry out this little tryout you will end up spending much more time trying to fix a panorama without knowing what you are doing, and without even knowing if you even have a chance to achieve what you want.

The idea is to "rotate" the panorama left or right, towards the top or the bottom, or around its center by selecting the Yaw, Pitch and Roll parameters and altering their values.

Options

  • Yaw = Right and Left offset (a positive value moves the panorama to the right).
  • Pitch = Up and Down offset (a positive value moves the panorama down).
  • Roll = Rotation around the set center point (a positive value rotates the panorama clockwise).

The panorama center is materialized by the point formed by the intersection of the vertical and horizontal grey lines displayed on top of the panorama.

The rotation angle is in degrees, the effects of this parameter are stacking: a -10° rotation cancels a previous 10° rotation.

A random use of this tool makes it difficult to understand as the effects are stacking, this would be an unfortunate approach as it is a very powerful tool.

Actions

  • Use the Enter key to validate the changes or click on Check on.png: The panorama’s preview will change to reflect the changes just requested.
  • To discard the changes and come back to the previous state, click on Check off.png.
  • To cancel an action after it is completed use the History by clicking on the History.png icon.


Cross center.png Set Center Point

Positionner le point de vue

This tool centers the panorama on the click location, implying two things:

  • It moves the center of the panorama left or right (the vertical grey line act as a guide).
  • It locates the horizon at the click’s height (the horizon grey line act as a guide).

Regarding left and right centering; note that when using a Planar Projection the perspective paths are affected by the location of the vertical grey line.

Note that when setting the vertical center (i.e. locating the horizon under the horizontal grey line), the click location should be located at the camera's height, unless you are looking for a low angle shot (verticals converging up) or a high angle shot (verticals converging down). To move the horizon up or down it is best to use the Set Verticals tool described in the next paragraph.

Autopan Pro will automatically estimate the location of the horizon before displaying the preview. If you think this estimation was acceptable after you made changes, you can click on Auto Level to go back to the estimated value calculated by Autopano Pro. This being said, it is important to keep in mind that Autopano Pro totally ignores what was photographed. You remain the best judge to determine what is right.

When using a Cylindrical or a Planar projection, the best way to offset the image to the right or to the left without altering anything else is to use the Numerical Transformation tool and acting only on the Yaw parameter.

Actions

  • Checking the "Center Point tool stays activated after use" box allow you to try different Center Point locations in a row without having to reselect the tool every time.
  • To cancel an action after it is completed use the History by clicking on the History.png icon.


Vertical1.png Set Verticals

Lignes verticales

This tool will allow you to straighten-up a panorama by placing vertical lines on the pictures. Here is how to use the tool:

  • Click on the Set Verticals tool, move your pointer over the preview then click/hold the left mouse button and drag the mouse to create and set a line, release the mouse button when done.
  • Locate the blue lines where you are sure there was a straight line in the subject (building corner, doors and windows, furniture). Two or three lines are generally enough, especially if they are far apart from each other, but you can use more as long as you know there is a straight line underneath (be careful with old building walls and with leaning telephone poles). The software will then find the best possible compromise, taking in account your input and the bonds created between the source images.

You can use the tool with a single line to do a quick rotation; the line you traced will then become a perfect vertical.

The yellow dotted line attached to the blue line is used to straighten the horizon. In landscape or nature photography is it quite frequent to shoot a subject with no verticals, when very often this subject will have a horizon. So instead of using a vertical as a guide you can adjust the verticals by placing the yellow dotted line on the horizon. The use of 3 or 4 lines on the horizon is generally enough to straighten it.

Note: the blue line should be traced from top to bottom to apply a small transformation to the panorama. If the blue line is made horizontally the panorama will rotate a quarter of a turn, if made from bottom to top the panorama will flip 180 degrees: You might be a little surprised by the results if you do not follow these guidelines, so be aware of the way you are creating the blue lines.

Options

The Horizontal line tool is used to straighten a crocked horizon. It works in the same way as the Verticals tool: You just need to draw a line on the line you want to be level. Be aware that this tool is only available in the Linear projection mode. If you wish to stay in Spherical or Cylindrical projection, use the doted yellow lines of the Verticals tool to locate the horizon.

Actions

  • To erase a line just click-select it and use the Delete keyboard key.
  • To modify a line’s orientation or its length, click-select the line then use the red handles located at each end of the line.
  • Use the Enter key to validate the changes or click on Check on.png: the panorama’s preview will change to reflect the changes just requested.
  • To ignore the line you just drew and come back to the previous state, click on Check off.png.
  • To cancel an action after it is completed use the History by clicking on the History.png icon.

More on this subject

Find out How to straighten a panorama using the Verticals tool.




Level.png Auto Level

Even if the original pictures where shoot with the lens pointing up or down Autopano Pro will often produce a leveled panorama, to a point where one could think that the tool doesn't work, as there is no visible difference between “before” and “after”!

If, in the other hand, the previous Yaw, Pitch and Roll tools were used to modify the panorama and/or if the center point was relocated, the effect of the Auto Level tool becomes visible.

Although Autopano Pro tries its best to produce acceptable results, it does not always succeed:

  • If the rotation axis of the camera wasn’t vertical when going from one shoot to the other (handheld shoot, tripod axis or panohead axis not well set) it is possible that parts of the resulting panorama will not be straight.
  • If all the pictures are leaning in the same direction (with a panohead this should no arise, with a tripod it's a difference between two settings), the whole panorama will not be straight.

In both cases the Set Verticals tool should be used to straighten everything up.

Actions

  • To cancel an action after it is completed use the History by clicking on the History.png icon.


Crop.png Crop

Tailler

This tool will allow you set the framing of the panorama. It works in the very same way as the Adobe Photoshop crop tool except that the original setting is automatically set to the maximum rectangular surface of the panorama. None of the rectangle’s surface is left empty; the automatic framing is quick and precise.

Options

  • Crop zone: The settings present under this heading will allow you to set the crop area very accurately:
    • Theta refers to the frame’s width
    • Phi refers to the frame’s height
    • Rotation is used to rotate the frame
    • Full Sphere is used to crop the panorama in case it belongs to a full spherical panorama (in some virtual tour cases)
  • Ratio is used to set the frame ratio, useful to set a panoramic crop for printing or framing, or to obtain a constant ratio across several panoramas.
  • Transparency is used to set the brightness of the area located outside the cropping frame in order to help visualizing the final effect.

Actions

  • Use the handles located on the outside edges of the frame to resize the cropping zone. Maintain the Ctrl keyboard key down to resize the frame from its center.
  • To move the frame around, place the mouse pointer inside the cropping area. It then changes into a hand.
  • To rotate the frame, place the mouse pointer outside the cropping area. It then changes into a rotation arrow.
  • To validate any change you made, press the keyboard Enter key, click on Check on.png, or double-click inside the rectangle: the panorama’s preview will then refresh to reflect the changes you just requested.
  • To discard the changes and come back to the previous state, click on Check off.png.
  • To cancel an action after it is completed use the History by clicking on the History.png icon.


Fit.png Auto Fit

When you press this button, the produced effect is the exact opposite of the one produced by the Crop tool: the panorama is included in a rectangle as big a needed to include all the pixels of the panorama.

If you previously used the Crop tool, then modified the panorama’s geometry, by let’s say applying a rotation, this tool is useful to recover the areas that are now excluded from the image.

As long as this button remains down the totality of the resulting image will remain visible, whatever you do.