In VFX today Gary has been teaching us how to lie. I mean teach us how to doctor pictures. I mean show us how to sky replace.

What surprised me is how easy it is to do. There was two ways we could do this, one with a Linear Key and another with a Colorama.

Firstly, the Linear Key. This is useful with skies (or I’m presuming other things not just skies) of one colour, like blue skies on sunny days – picture below.



So to begin with I found a starry night sky and added this and the above picture into After Effects. Then I duplicated the picture and inserted the stars in between these. Next, I added the Linear wipe to the middle, starry, layer (Effects > Liner Wipe) and altered the transition to 30% and Wipe Angle to 0.

NB. I later found out that the transition can be altered from picture to picture as a 30% transition cuts off the bottom 30% of the picture, therefore a 50% transition would cut off the bottom 50% etc. How much cut off is needed depends on the pictures being blended.


Next, I checked the eye button to hide the top layer and dragged the feathering option to an amount which helped the pictures blend together. In this case a 2.0 feather seemed to work well.

The top layer was turned back on again and now I found a Linear Colour Key through the Effects and Presets panel applying it to this top layer. From here I used the dropper tool and selected the blue sky. Immediately the blue sky disappeared and was replaced with the starry sky.















After this I practiced on a couple of other shots with sunsets;


I’ve used the same techniques with pictures 2 and 3 as I have with one but as I’ve gotten to know what I’m doing that little better I feel like I’ve been able to blend the pictures together with better results, especially with the city skyline above. I know and can see there’s a few parts that would need more detailed work to, but I’m proud of what I’ve made nonetheless.

I did try the Colorama method too on a fourth picture where the cloudy sky of the beach picture above would be removed and replaced with the clear blue but as you can see from the two images on the right, something went a bit skew-iff. I do have the tutorial on my hard drve and when I get a few spare minutes I’m going to try again and sky replace this picture. I’ll update the post when I do.



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