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Rectify Grid Settings

The settings for the Rectify Grid tool are similar to those of Lens Master Calibration. As always, you can also check the tooltips on the Rectify Grid control panel.

Lens workflow. Drop-down. One-Pass: the output image is the final fully-filled image; some original pixels will be 'cut off.' You must set Fixed size override to specify your desired final image size. Two-Pass: the output image is large enough to contain the undistorted image, containing all possible usable pixels. Typically you will render CGI matching the undistorted image, then redistort it and composite to the originals.

Lens Name Override. Text. You can specify a different lens name here, it is used for the preset name and image map names, so just use simple safe characters such as A-Z, a-z, 0- 9, underscore, and dash.

Put preset/map... Drop-down. With scene file/With image file/in User preset folder/in System preset folder/Other. This dropdown controls where the generated preset and/or image maps will be placed. To make it available for selection on the image preprocessor's lens tab, it needs to be placed in the user or system preset folder. (You must have appropriate operating- system permissions to write to the system preset folder.)

'Other' folder for preset...Browse. Browsable folder. When the Put preset/map... dropdown is set to Other, this field supplies the folder name.

Image Map type. Drop-down. Selects the file type for image maps. It must always support floating point, or at least 16bit, formats. See 'Lens Distortion Interchange via Image Distortion Maps' in the SynthEyes User Manual for discussion.

Map compression. Button. Bring up the compression settings dialog for the selected image map type. Compressing a map file must be done with care: do not use lossy compression methods!

Maintain resolution. Checkbox. When checked using Workflow #2, the output image size will be increased to try to maintain pixel density equivalent to the original image at its center. Recommended!

Square pixels. Checkbox. Make the undistorted image have square pixels, even if they aren't in the original image. This may make rendering and viewing matching footage simpler and less non-standard. Using the two-pass lens workflow, 1:1 intermediate footage will be undistorted back to the original non-square pixel aspect ratio.

Size adjust (%). Number. Increase the output (undistorted) image size by this many percent from the distorted image size. Most commonly used when Maintain resolution is off; this control allows a common large-ish undistorted image size to be used.

Extra padding. Number. This is the number of extra safety pixels around the edge of workflow #2 images. Applied before any final width/height/aspect/by16 override.

Preserve image aspect. Checkbox. When on, the undistorted image will have the same aspect ratio as the original, keeping it simple but perhaps with a slightly larger image. When off, you must be sure to set the image aspect ratio in other apps appropriately (which is simpler if Square pixels is on).

Multiple of 16. Checkbox. When changing the image resolution, make sure the new width is a multiple of 16, which is required for some codecs.

Fixed size override. Text. You can enter a width and height value (separated by a space) to set the final undistorted image size exactly (for example “1920 1080”). Required in one-pass mode!

Overrange OK in map. Checkbox. Turn this on if you want to see red and green values over 1 or under 0 in the image maps for off-edge pixels. These may allow out-of-window pixels to be used in some apps.

Write alpha. Checkbox. Include an alpha channel in the output maps (if supported by file type).

Apply fix to scene. Checkbox. When checked (usually), the newly-computed lens distortion map is applied to the scene, so that you see the final undistorted version of the grid image.

Write scripts. Checkbox. Write Sizzle scripts to configure the image preprocessor to later undistort or redistort a just-opened shot using the image maps we’re producing now. This makes setup easier and more accurate. The scripts are written to the same folders (and same names) as the image maps. Use Script/Run Script to run the script and apply the map preset.

Rough tilt correction. Checkbox. When enabled, Rectify Grid attempts to determine and correct for any off-perpendicular tilt between the camera and lens grid. Off-perpendicularity will result in subtle local shifts embedded in the calibration. Tilt correction will reduce but likely not eliminate them. This correction is necessarily only approximate, so you should make every effort to keep the camera perpendicular to the grid.

Physical grid spacing. Number. The physical spacing between dots, or the size of the checkerboard squares, in the physical lens grid object. This can be measured in any convenient units, typically centimeters or inches, as long as it matches the following distance number.

Preferably this number should be obtained from the construction of the grid; if it must be measured, measure 10 and divide by ten to increase accuracy (or use the entire grid). Note that the horizontal and vertical spacing must always be the same, so only one number is required.

Physical grid distance. Number. The distance between the nodal point of the camera, at the center of the lens’s entrance iris (inside the lens), and the lens grid, along the optic axis of the camera, ie to where the center of the camera view falls on the screen. Measure with the same units as for the grid spacing.

One more thing: Polynomial fit. Checkbox. This brings up an experimental user interface and capability in Rectify: instead of the normal non-fitted “perfect rectification” behavior, it does perform a high-order but dumb polynomial fit, followed by synthesizing a fake tracker grid, then doing the rectification. This can allow a grid to be extended (as does the normal Lens Master Calibration) though this has a large set of coefficients for anamorphic lenses. This is experimental in the sense that it’s new quick experimental code, but also in that it is for doing experiments to see what’s necessary. Start small, don’t turn all the checkboxes on! It can easily produce total garbage. There is an additional capability (Two more things!) here that seems to need some more finesse.

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