Zenith and Nadir editing overview

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Intro

One of the most problematic points when shooting spherical panoramas is the view straight down also called the Nadir view. Either the tripod is visible or there may be alignment or color mismatches if shooting handheld.

Unfortunately neither the nadir nor the zenith (straight above) area can be edited directly in the equirectangular image since it is very distorted. For this taske we need to either extract a partial view pointing straight up or down or we can cover the relevant section by something else - a mirror ball or a logo f.e.

You find several pages that desribe how to do that. This one is intended to give an overview of the different techniques.

Patching Nadir

There are several reasons why you want to patch Nadir and retouche it such, that nothing of the photographer and his equipement is seen any more. One is that it is somehow annoying if you view a full screen spherical pano and feel very immersed and something not belonging to the scene like a logo pops into sight.

The easiest way to achieve this is to simply shoot nadir. Step aside and shoot roughly from the same position straight down. This gets complicated if the floor is not even or if there are details in different heights because you get parallaxe errors. You will need to use a special stitching workflow to get this right. See Stitching Nadir Shots for details.

If you need to patch Nadir after shooting you need to either move it to a location where it can be edited or extract a view for editing.

Moving Nadir

This technique remaps the whole panorama such that Nadir is on the equator and hence almost undistorted. Zenith can be edited in the same image. The disadvantage is that if you have regular patterns on the floor that you could use for filling the hole they are distorted the further away from the hole they are. Hence this technique seems to be good for small nadir holes or floor with irregular patterns like sand, grass or leaves only:

• Edit zenith and nadir in one go with PTGui
• Edit zenith and nadir in one go with Adjust filter

Extracting and Inserting Nadir

Not as convenient as moving nadir is to extract a rectilinear view, patch it and insert it back into the panorama. This way straight patterns like rectangular stones or wooden planks stay straight and equal spaced, hence it is very easy to patch the floor.

There is a comprehensive overview in Extracting and inserting rectilinear Views and a special tutorial on How to use PTEditor for that task.

Patching techniques

In both cases you need a technique to patch Nadir. One of the most powerfull requires an image editor capable of using layers. Here a workflow for Photoshop:

• Open image to patch
• Keep the layers palette open
• Create layer from background by double clicking it in the layers palette.
• In the layers palette duplicate layer by dragging the layer thumbnail to the 'Create new layer' icon in the footer line.
• Add a mask to the top layer by clicking the 'Add vector mask' icon in the footer line
• Make bottom layer invisible by clicking on it's eye symbol
• Make the mask the painting destination by clicking it in the layers palette.
• Choose a soft brush and black as painting color.
• Paint the mask black where you want to retouche the image - this should result in a hole in the image
• Switch the bottom layers visibility on again.
• Click the bottom layers thumbnail to make it painting destination
• Choose the Move Tool and move the layer by dragging in the image to place some other parts of the floor in the hole in the upper layer
• Edit seams of the mask to your need.
• Once your'e done flatten and save.

There are numerous other techniques to patch an image, including using the patch tool (which requires the area to be patched having similar color and brightness as the surroundings) or the clone stamp. A very nice one that is capable of blending the patched area with equalization of color is described in Using enblend to fill the "Hole in the floor"

Replacing Nadir

The easiest way to cover a tripod head or a hole is to place something else over it. This can be a logo or f.e. a mirror ball. The latter is nice, because it doesn't affect the 'immersive feeling' that much - it could well be part of the scene:

• Adding a nadir cap (mirror ball)
• Adding a nadir logo with text

Erik Krause 16:31, 24 Apr 2005 (EDT)