Tutorial: Adding texture underneath an object

4.7. Tutorial: Adding texture underneath an object

Problem

Because the object is placed on a stand and pictures taken showing the calibration mat, the underneath of the object is not visible in any of the images. When you build the textured model, the underneath of the model is textured with a plain colour guessed from the surrounding geometry.

Solution

In many cases the plain texture (as seen in Figure 4.7.4) is adequate since you may not be interested in the bottom of the object or it may be plain anyway. If you do want to add texture, the simplest approach with 3DSOM Pro is to turn the object over and take one or two images of the base of the object and add these to the project manually.

Figure 4.7.1. An additional image from underneath the doll figurine.

3DSOM Pro will not be able to locate the camera position for these underneath shots. The Align Wizard is used to manually align each of these additional images relative to the others in the project so that they can be used when generating the texture map.

Starting Point

Create a new project and load in all the photographs. The underneath images without the calibration mat will be marked as "rejected". Alternatively, you can load all the images except the underneath ones, and then add them to the project at the end of this step.

Generate masks for the rest of the images and build the geometry as normal.

TIP:	If the object has few geometrical features but a lot of texture features, it may also be worth generating the surface texture (excluding the underneath) at this stage to help with the alignment.

Step 1

Select the underneath images (it doesn't matter if they are currently marked as rejected) and choose Images > Align Images... menu item. This will open the Align Wizard and update the Thumbnail Window.

The "Align Each Image" option should be selected on the Alignment Wizard: Task Page — each additional image will have to be aligned separately in turn.

Choose Next > button to move onto the next page.

Step 2

At this point, look at View Model Window - it displays the current model semi-transparently over the first of the additional images.

TIP:	It might help to use the wireframe display mode and change the colour of the wireframe from the 3DSOM Pro Settings Window.

Position and orient the model so that it matches the image displayed behind it using the Rotate model button, Move model button, Zoom model button and Spin model button buttons as normal. Use the Next view button (and the Last view button) on the View Model toolbar if you want to move back to where you were previously.

Figure 4.7.2. Wireframe doll before aligning to the underneath image.

Figure 4.7.3. Wireframe doll now aligned with the underneath image.

To position the model more accurately, you may want to see the image in more detail - use the Magnify View button and Pan View button tools to enlarge and move around the background image while you position the model.

Using "Optimise Alignment"

You can use the automatic alignment feature of 3DSOM Pro to fine tune the alignment of an additional image, but to do so you will need to have created an accurate mask for the additional image before opening the Align Wizard.

Press the Start button and wait for the model to be adjusted. Press the Stop button at any point to finish.

Step 3

When you are happy with the alignment of the first image, use the Next image button to move onto the next one. You can always return to the other images later if you wish, but note that pressing Cancel button will keep all the changes you have made to the alignment of all images other than the one currently displayed.

TIP:	You can also simply double-click on one of the additional images in the Thumbnail Window or drag an image from the Thumbnail Window onto the View Model Window to use this as the background image.

When you have aligned all the images you want to, click the Next > button at the bottom if the window to proceed to the final page.

Step 4

Closing the wizard will set the camera orientation for all of the underneath images that you have aligned by hand. 3DSOM Pro will also create masks for each of them using the existing geometry.

They can now be used in the project in the same way that the original set of images were. You can now generate the textures including these images.

Figure 4.7.4. Doll model with no images from underneath.

Figure 4.7.5. Final doll model using manually aligned underneath image.

TIP:	If you have already created an edited texture map you can merge in just the underneath images by selecting each in turn from the Thumbnail Window and then using the Images > Paste Into Model menu item (alternatively, hold Ctrl and drag the thumbnail onto the View Model Window).

You can further adjust the alignment for one or more underneath images by selecting the thumbnails and opening the Align Wizard. You will start the alignment where you left off previously.