Import arm and its division to Photoshop, fill them with color black, create a new layer, and Ctrl + click the division layer to get its selection. Hide the arm layer then add a layer mask to the division layer, now select a soft brush of size 100px and color #434343 and paint through the one side of the arm to make it shading, now unhide the arm layer.
Next, select brush of color #787878 and create lights on another side of the arm, experiment with the opacity of brush and size to get the best results, again select another brush of color #9d9d9d and create bright light to create finer lights on the arm. Be careful while creating lights and pay attention to the direction of light and light source to create natural light.
Now select a soft brush of color black and add shadows to the highlighted areas by red color. Experiment with opacity and size of brushes to get perfect results.
Next, select arm layer and press Ctrl + click on arm layer to get its selection then go to Select > Modify > Contract and contract the selection to 4 pixels then add a layer mask to the layer. You will get finer divisions in the arm, repeat the same procedure from step 5 to step 11 to create other arms too and place them into our scene. If everything is done right, then your result may look like this.
Step 12 – Adding demolition to buildings.
Group arm layers, right-click and convert it to smart object and rename arm to “tentacle”, again group all tentacles and name this group to “tentacles”. After placing octopus arms, we have a rough idea about which building to be demolished and where destruction to be added. So, let’s start with center building, select the pen tool, turn shape layer on and create a demolition area. In this area, we will add destruction to the building, name this layer to “demolition area”.
Fill that area to color black, import “demolished building 1.jpg” and isolate its demolished part. Duplicate this texture, transform and flip horizontal and vertical to extend the texture. Use the clone stamp tool to extend texture seamlessly.
Clip mask this texture inside “demolition area” layer, Ctrl + click on this layer, select a soft brush of color black and create shadows along edges of the area. Create some windows to match with the building structure, so create some window squares filled with color black then add some more shadows to it.
To make destruction more realistic we need to add some cracks to the walls. Select brush tool, right-click and load “crack1.abr” & “crack2.abr” brushes. Select any crack brush and create cracks along the edge of demolition.
Next, we will add destruction to the right side of the building for this, create another demolition area, import “demolished building 4.jpg” and clip mask this image to the demolition area. Add shadows inside the edges and cracks outside to the demolition area. Add a layer mask and hide unnecessary part of the demolition.
Now you can notice that after hiding the right part of demolition has revealed the original undamaged part of the building. Select the city layer then select the clone stamp tool and clone roads and shadows of buildings in the background.
Open “demolition.jpg”, remove its background and place it below the building. Add some shadows relative to our source of light, this will give our scene more realism. Repeat this step to add demolished scrap to other buildings too.