"Stereo Framing: Lesson 1" transcript
©2011 Eleanor (Lea) Tesoro / Opal Lei. All rights reserved.
Welcome! My name is Eleanor Tesoro, known in Second Life as Opal Lei. This video is part of a series of tutorials on Stereomasken.
To install Stereomasken, go to www.stereomasken.de. In this tutorial, I am using version 1.20, which is the b.zip file in the English version on a PC.
In Lesson 1, we will cover opening a pair of stereo files and talk about the basic concepts of stereoscopy, then we will create a rectangular frame, then we will save the new framed stereo pair.
OPENING A STEREO PAIR
We start by loading a pair of stereo photos.
Stereomasken saves the mask in a file, separate from the stereo pair. So the mask can be loaded and used with another stereo pair. But, since we are creating a new mask entirely, we only need to open the stereo pair. We can do that either by clicking this icon in the icon bar or by choosing File > "Open Left and Right Image".
Under Choose Input Format, be sure to select "Two images: left and right". Then click "Choose Files" and find the files you want.
Choose the left eye photo first and open it. Notice that, after choosing the first file, Stereomasken infers the name of the second file by replacing the last letter in the file name.
To preview the thumbnails, click on the "Cross View" icon and view the thumbnails cross-eyed. If the stereo looks like it's inside out, click "Swap Images" so they would look right. Then click OK.
BASIC CONCEPTS OF STEREOSCOPY
In this photo, I have objects that recede to the background in stages. My avatar is in the foreground, then I have the mermaid sculpture and the pelicans, the number "5" and the balls below it, the rocks, then the skull and the mountain.
We know that my avatar is in front of the skull, because the avatar covers part of the skull. That's called occlusion, and it is one way the brain determines depth, especially in a two-dimensional photo.
Another way that the brain determines depth is by the differences between the left and the right images. Look at the images separately. Notice how my avatar shifted between the two images. In one image, one eye of the skull is completely covered by my avatar. My scarf went from here ... to here. That is a wide shift.
In comparison, look how the head of the left pelican shifted compared to the plants on the mountainside On the left side, it starts at this point. Then it moves slightly to the right, from here to here. That is a smaller shift. And that's because the pelican is farther away from the viewer than my avatar is.
FRAMES WITH DEPTH
The edges of the pictures comprise the frame. And the frame in a stereo pair also has depth. View this pair cross-eyed and look at the upper part. Particularly the upper left part.
The shift in the position of the frame edges tells our brains that the frame is behind the mountain. At the same time, the frame covers parts of the objects in the foreground, and, in terms of occlusion, the frame must logically be in front of those objects. Is it behind the mountain or is it in front of the foreground objects? The brain tries to resolve the inconsistency. But it cannot. So we feel uncomfortable looking at it. In stereoscopy terms, we call it a window violation.
The simplest fix to a window violation is to move the window forward. In future lessons, I will teach you how to SHAPE a window, but let's start with the basics.
CREATING MASK POINTS
Framing is essentially selecting which parts of the photos we want to keep.
In this lesson, we are going to create a simple rectangular frame, so we start with creating a mask with four points.
This group of icons in the icon bar has to do with manipulating the points in a mask. Create, edit, delete. The functionality is also available in the Mask menu. Create, Edit, Delete. By selecting one of these, you are changing the mode of your mouse clicks.
We start by creating new points by going into the Create mode. Just click this icon or choose Mask > "Create New Mask Points". If the icon is already depressed, that means you are already in that mode.
Click on the photo on the right side to create the initial shape of the mask. I prefer to define the mask on this side, because the depth is defined by the mask on the left side, and I'll demonstrate that later.
To switch to the Edit mode, click this icon or choose Mask > "Edit Mask Points". Notice, that after creating the third point, the rest of the photo turns green to show which parts of the photo will be cropped out. You can change that setting with this icon or go to View and toggle the "Transparent Mask" option.
SELECTING MASK POINTS
The points that are currently selected are yellow and the points that are deselected are green. To deselect all points, click anywhere outside the mask until they're all green.
To select the first point, you simply click on it, and to select additional points, you hold down the Shift key and click. When aligning, the second point and subsequent points will be adjusted to match the first selected point.
In cases where you don't care which point is the first selected point, you can simply draw a selection box around the points you want.
POSITIONING MASK POINTS
These icons allow you to shift selected points in different directions: up and down in the y axis, left and right in the x axis, or in any direction on the XY plane. And this is the icon that shifts the depth. The same functionality is available in the Move menu; "Shift to Stereo Window", "Shift in Depth", "Shift in X", "Shift in Y".
Now, let's select a point and try out these modes.
"Shift in Y" allows us to move up and down, but not left and right.
"Shift in X" allows us to move left and right, but not up and down.
"Shift to stereo window" allows us to move in any direction in the XY plane.
Now, cross your eyes. Notice that the frame created by the mask is still behind the mountain.
So I'm going to select all points. Then choose "Shift in Depth".
Now, watch as I move the frame forward, so that it looks as though it is in front of the avatar. ... In front of the avatar ... Behind the avatar ... In front of the avatar ... Behind the avatar ....
Now, UNcross your eyes and notice that the left mask is moving left and right, and the right mask remains static. In this mode, I cannot move the points up or down, because depth is defined by the horizontal shift, not the vertical shift. That is because our eyes are aligned horizontally, so our brains are programmed to determine depth by horizontal shifts, not vertical shifts. ... Of course, "horizontal" depends on the position of your head. So if you tilt your head, "horizontal" is the same level as your eyes.
ALIGNING MASK POINTS
Let's go back to shifting the points in the XY plane.
This group of icons makes it easy to align the points -- we can do that either horizontally, vertically or in depth. The same functionality is available in the Align menu... "Adjust Horizontally", "Adjust vertically", "Adjust Depth".
In order to use them, you must first select at least two points.
So, let's align the points to make a nice rectangle.
Click on the first point, then Shift-click the second point, then "Adjust Horizontally".
Notice that the second point adjusted itself up to the same level as the first point.
Now, let's do the bottom edge. Click, Shift-click, Align Horizontally.
Now, the vertical.
CHANGING MASK SETTINGS
Now that we have the frame adjusted, we can adjust the mask settings by going to Edit > Settings. We can change the color of the mask here. Color of Mask >Edit Color ... then choose the color you want... and click OK.
I usually prefer to save my mask as white for two reasons: 1. white is least distracting especially if the background is also white. and 2. white is easy to mask out in Gimp or any other photo editor just in case you decide to change your background to transparent.
Stereomasken also adds a fine border around the frame. Like this one. You can choose to leave it as a decorative element and adjust its properties by going to Outline Frame and adjusting it right here. However, it is only ideal if all points of the stereo frame is on the xy plane, because the width of the frame [line] is the same throughout, which causes a disparity when the stereo frame flows forwards and backwards. Our brains expect things to get smaller as they get farther away; that is, the width of the line must also get narrower. So it is not a problem with the frame we created today, but it could be a problem in frames that we create in future lessons.
So, for now, uncheck the Apply box and click OK.
SAVING THE STEREO PAIR
Now, to save the stereo pair and the mask, then use this icon "Save Masked Left and Right Image", or go to File > "Save Masked Left and Right Image".
If the files already exist, they will show up as red. You can check Overwrite and they will turn blue. Be sure to select bitmap to avoid lossiness with JPG.
If you want to change the directory where you want to save them, click "Choose Files".
Otherwise, just click OK. And say "Yes" to the confirmation.
This concludes Lesson 1 of Stereo Framing with Stereomasken.
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My name is Opal Lei. Thanks for watching.