Written by Juan Gayarre of GAYARRE infografía

INTRODUCTION

The addition of sky time-lapses to video and architectural visualization productions is not new. 

This addition to both still as moving scenes is not complicated, as you will see in this easy tutorial. The most complicated issue is obtaining these kinds of files. There are two ways: filming them yourself or getting them from the Internet.

I encourage you to try.  Just go out with your camera. Find the right shooting spot. Be patient and film a few hours. Accelerate the outcome. Do the sequence’s post-production deleting defects and, eventually, prepare the final sequence in HD.

You will soon find it’s quite technically difficult and requires time to get the quality and characteristics desired to use the final files in production.

I encourage you to choose the second option: acquire our skies.

This tutorial will teach you how to do the post-production process with our videos. I will show you how to perform the post-production, the versatility of this files in order to convert still images into moving sequences and how they contribute to enhance your video works. We’ll focus on the details that will make our post-production both credible and professional.

FIRST STEP: PREPARING THE IMAGES

Although it can be applied to moving images, the concepts are the same. The only variation is the time line evolution of the masks.

We prepare the scene using Photoshop.

We select the alpha channel where our time-lapse will move initially.

It will be necessary to shrink the selection borders by one or two pixels in order to make it work properly.

We must understand that adding a sky with accelerated movement to one scene brings consequences. We can’t just add the sky and forget about the rest. What do I mean by this?

If a sky is cloudy, like the one used in this example,  and the scene shows a sunny day, the clouds will have a shadow on the ground. There should be a consistency between the clouds and what they cause, between their movement and the shadows they cause.

We generate a new alpha for each scene that interacts with the sky. Afterwards we select the areas where the shadows of the clouds will apply: ground, trees, etc. differentiating all the different panes.

If our scene includes glass, it will reflect the movement of the clouds. We select upfront the glass that are reflecting.

Please bare in mind that the shadowed areas are not affected, so there’s no need to choose them. Each alpha has to be saved as a black and white file in a folder we previously prepared.

SECOND STEP: AFTER EFFECTS, OUR COOKING KITCHEN

Once we have prepared all our Photoshop files, we have to combine them properly in After Effects.

Let’s import the files we saved:

The render

The time-lapse

The alpha channels

Drag the render or the time-lapse to our composition. When arranging the layers, we’ll obviously set the render in front and the sky behind. This one will be trimmed when applying the matching alpha channel.

First we have to determine the direction of the light. Both layers, render and sky have to be consistent. Normally, the render gives us a hint. We can know the approximate position of the sun by looking at the shadows. Once this position is settled, we can probe the proper sky orientation. Trial and error is the best system in this situation. There are only two possibilities: option A or B as a result of the horizontal flip of the sequence. Only experience will help deciding which fits better.

Next step is retouching the parameters of the sky: brightness-contrast, saturation, … until it fits our scene.

THIRD STEP: APPLYING MASKS IN AFTER EFFECTS

We have to activate the MODES column in the LAYERS panel. This way, we define each layer’s alpha (previously saved file in black and white).

We drag the desired mask to our composition and duplicate the sky. We apply matte luma mode. This way, the sky layer will have the layer above as alpha. Try it. It’s easier doing it than explaining it ;)

REFLECTIONS

We’ll generate the sky’s reflections on windows and reflecting materials. We should not forget about horizontally flipping the sky’s time-lapse in the reflections. If a cloud fades to the right, the reflection will do it to the left.

If the mask is not too complex, we can also generate it manually in After Effects.

SHADOWS

In order to generate the shadows, we’ll duplicate the time-lapse layer, desaturate, blur, invert the color and play with the color values in tone/saturation, until we find the desired effect.

We leave the fusion style as multiply.

As with the reflections, shadows need also a correspondence between movement and shape wherever we apply them. For example, we slightly rotate the shadow in a perspective area in order to create a movement effect from back to front or front to back.

We can give our images a new dimension by applying these easy steps, transforming a still image into a moving one. We can introduce one new element in order to get a more realistic video effect.

After creating a null object, we select all the layers and link them to this null object (primary-null1). Now we just have to animate the null the way we want, and we get a moving video pane.

We can modify the masks we created by blurring the edges to deleting areas where shadows or reflections are not to be applied with high intensity.

I hope this guide helps you to start up. It’s a starting point. You will need to improve on the final result for a perfect integration. Each case is different and needs hours of trial and error to get good results.

Go to 1:05 to see the Timelapse skies examples.