Detailed analysis of the base projection informed the strategy for addressing the resolution issues and patching the areas affected by artefacts such as texture doubling, smearing, missing coverage and insufficient image resolution.
Image Set A
A single patch is required to fix the doubling artefact on the roof and window on the rightmost building of this set. The image below) is taken from the shot camera on frame 38 but with a reduced focal length of 35 and rendered with a commensurate increase in resolution to compensate for the Overscanning.
This projection setup allows the affected area of the roof to be corrected and also provide texture to patch the extreme elements of both buildings where texture smearing and potential loss of resolution s present.
The image (below shows the patch, confined just to the offending areas using masks.
This image, taken from frame 20, shows the successful repair to the roof on the rightmost building.
This image, taken from frame 40, shows reinstatement of texture resolution on the dome (left) and the stone wall (right).
Image Set B
A single patch projection is required for the set in order to fix the loss of resolution on the stone texture at the far side of the arch, evident in the latter stages of the shot as the camera passes. This was anticipated during the checkerboard projection test and visible when the base texture is applied. This also revealed a small amount of texture doubling in the window areas on both sides of the arch.
A patch camera was created by backing off to frame 75 so as to remain within the resolution threshold and with an Overscan to extend the coverage enough to bring the windows into view and therefore allowing these to be fixed as part of the same projection. The image (below) shows the patch, rendered at a higher resolution (based on a calculation established in previous projects) in order to compensate for the magnifying effect of the wider focal length.
The patch is constrained to the affected areas only using masks on the alpha channel.
The image (below) shows the layered section constrained to the affected area with no overlap onto adjacent surfaces. The green tint is applied temporarily, just to highlight the effect of the mask
The image below shows a section of the leftmost arch at frame 75. Note that resolution is restored to the stone texture and the doubling artefacts on the window have been overpainted.
Image Set C
Minor texture doubling was present on both buildings in this set following application of the base texture.
On the leftmost building the brick texture on the front arch is doubling into the recess and onto the rear tower. The stair areas on both buildings are also affected by this artefact.
My first patch on leftmost building is derived from the shot camera on frame 98 with Overscan of 38 added to capture the full front façade. The affected areas on the archway, rear tower and steps are painted and the patch is reprojected over the base texture.
The image below shows further doubling evident on the building later in the sequence, in this case frame 105.
The shot camera is advanced to frame 115 to expose more doubling and then overscanned to reveal the full stepway
The image below shows the completed patch
For the walkway on the rightmost building in this set, a camera was derived from the shot camera on frame 112 and an Overscan added to bring both pillars into frame in case these are needed for masking
The image (below) shows the patch
From frame 100 the patches can be seen to have fixed the offending areas.
Image Set D
For this set, implementation of the projection strategy requires cameras, taken from the motion path of the shot camera, at frames 0, 80, 115, 140 and 200. The base projection, seen below from frame 80 shows the removal of the near-most tower and patio elements such as the rails, pillars and lamps.
Other that the separating of these elements for projection via their own shaders, the rightmost building is unaffected by projection artefacts. This is because the building rotates very minimally from the perspective of the shot camera so the only issue is maintaining resolution up to frame 140 when it is entirely off screen.
The leftmost building is a different proposition entirely as this acts as the ‘hero’ building that the camera rotates to frame its patio area and eventually settles to form the end view.
Note that some texture doubling is evident following the base projection.
The next logical step is to work out whether these areas are visible to the shot camera, once all the other geometry is in place. The video (below) shows the areas of this structure that are occluded by other geometric objects from the shot camera perspective.
The benefits of taking this step are really valuable yet extremely simple conceptually. Because camera-projected matte painting is only ever concerned with what the shot camera sees, there is no need to patch anything that is obscured and indeed, to do so would be a waste of time and effort.
Additional work is needed to fix an area of texture doubling on the patio of the building. The image (below) shows image from the perspective of the shot camera on frame 170. Note how strips of texture from the upper edge of the steps, double across the patio.
Initial tests patching the area using projection camera along the path of the shot camera proved unsuccessful as the offending artefacts reappeared every few frames. My estimation was that, over the affected duration (frames 115 to 200) a new patch would be needed every five frames. This equates to 17 patches which is clearly excessive in terms of time and effort.
There was scope to split the stepway geometry from the main structure and construct a separate shader network, similar to the approach taken with the patio elements and protruding parts of the structure. However I wanted to first experiment with a different approach, which was to perform more of an orthographic projection by completely breaking a camera from the motion path and transforming it to create a top down view.
A coverage render could be taken from this vantage point, repaired, and reprojected from the same camera. The patch could be constrained to just the patio using a mask on the alpha channel.
The marching ants show the boundaries of the patch following a cloning operation in Photoshop. This will be the area defined by the alpha channel.
Once the patch is projected onto the geometry, using the orthographic camera, the area of texture doubling, and smearing is repaired. A single patch addresses the issue across all the offending frames, seen below from frame 170.
Image Set E
No patch projections were required on this image set. Moreover the default projections all provided overlap where natural joins in the geometry could be used to terminate the alphas.
The image pair (below) shows the leftmost building from the standard projection camera on frame 200. Note how the mask terminates the texture along the border of the brickwork above the windows. A small amount of alpha blending is used on the right to fade in to the shadows in the recesses.
The Ground
Minimal work was needed on the ground other than some texture smearing on front face of curb.
This was resolved using an approach similar to that used to repair the patio area on image set D. A patch camera was broken from the moving shot camera path at frame 200, rotated and translated to provide an orthographic view of the offending curb. A coverage render was taken, patch-painted and then reprojected back over the geometry. A mask was used to limit the patch to just the curb.
The following video shows the ground playing through all frames with with the curb patched
Peter Holmes PhD Journal 