Tutoriel pour faire un diaporama animé

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Synfig propose plusieurs manières de créer un diaporama depuis une séries d'images. La plus simple est probablement d'utiliser l'import de séquence pour importer une séries d'images. Cependant, cette méthode qui fonctionne pour des images matricielles est incapable de générer des transitions. La technique expliquée ici est légèrement plus complexe, mais elle permet de créer une présentation depuis une série de calques indépendamment de leur taille ou type. Cette méthode réalise un effet de fondu enchaîné; un effet plus complexe nécessite une technique plus avancée.

Description Technique

Synfig crée les animations à partir d'une série de calques, ils existeront tout le long de l'axe de temps. L'objectif ici est de rendre visible chaque calques durant un temps donné. Même s'il existe plusieurs façons d'atteindre cet objectif, ce tutoriel explique comment garantir que un seul calque soit visible grâce aux Paramètres du Mode de Fusion et (en) Quantité de chacun des calques.

Tous les calques graphiques dans Synfig ont ces deux propriétés essentielles. Le Paramètres du Mode de Fusion définit comment l'image vas être mélangé avec celles du dessous, la quantité définit l'ampleur du mélange. Dans le mode de fusion par défaut, Composé, les objets sont simplement placés les un au dessus des autres. Dans ce cas, la valeur Quantité détermine le niveau de transparence global du calque : avec une valeur de 1.0, le calque est entièrement visible, avec une valeur de 0.0, il est entièrement transparent. Entre les deux, les valeurs correspondent à une transparence partielle, c'est ce qui vas créer la transition. These properties can be used to display a series of pictures. Each is its own layer and at any given point in time, one layer's amount is set to 1.0 while all others equal 0. However, there is a more efficient way of accomplishing the task. This method requires switching all images to the Straight blend mode.

This blend mode has an advantage: all layers below the current one are hidden. Therefore it is no longer necessary for layers below the current one to have a an Amount of 0. Using the Amount for crossfade still works, but it now needs to be changed only once: all layers start with a value of 1, and then be made transparent from the highest to the lowest.

The effect could be animated with two waypoints per layer. However, Synfig offers an even simpler method that does not require using the animation mode. Instead, linking functionality can be used. The data type for Amount is currently set to be a real number. Instead, let's replace that with a special function by converting the layer to Timed Swap.

Now we examine the parameters of this new data type. The first is the initial value (1.0), the second is the final value (0.0), and the third is the time when the values will switch. If we want the image to display for two seconds, we can set the Swap Time to "2s". (Note: this assumes we are starting at 0s). Then the amount will be 1.0 for three seconds (image visible) and 0 for the remainder of the timeline (image hidden). The last value will be the duration of the crossfade transition. Note that the transition takes away from the time for which the image will be displayed. For example, a value of "1s" means that the image will be fully opaque for one second, fade in one second, and then remain faded for the remainder of the animation.

Applying successive times to layers from the top down will fade them one by one, creating the desired slideshow effect.

Step-by-Step Instructions

Here are step-by-step instructions for applying this principle to an animation.

Setting Up

Open a Synfig document and import any images, canvases, etc. Images can be imported using >File>Import (The first ">" signifies the Caret Menu). Note that importing links to the image using a relative path. Take care to maintain the relative positions of the files when moving them. If multiple layers represent a single image, encapsulate them into an Inline Canvas. Then arrange the images in the order they will be displayed, first image on top.

Blend Method

Select all layers in the layer panel. Then go to the parameters panel and set the Blend Method to Straight.

Timed Swap

Unlike Blend Mode, converting to Timed Swap must be done individually for each layer. Set "Before" to 1.0 and "After" to 0. Suppose you want the images to swap every 4 seconds, using 1 second transitions. Then set the "Duration" to "1s". Afterwards, set Time for the first layer to 4+1=5. Then increase the time for each successive layer (5,10,15,20,...). The Swap Time is the point where the image fully disappears. Configure these values to fit your needs.

Animation Length

Now that times have been configured, your file must be configured to render the full animation length. Go to >Edit>Properties and switch to the "Time" tab. Set the end time to equal the last of your time values. You can add a few seconds if you want a blank/black screen at the end, after the images have faded.

Extra: Background

You may have noticed that the Straight Blend Mode removes any backgrounds from the image. Here are two methods to add a background:

a) Encapsulate all image layers. Now the Straight blend mode only works within the inline canvas. Once this is done, add any backgrounds below the canvas, and any foreground above the canvas.

b) Add a background layer/canvas to the top of the layer list. Since it is above all other layers, the Straight layering mode doesn't affect it. However, it would normally shroud all the images. To make it appear below everything else, set the Blend Mode to Behind.

Endnotes

Congratulations! You have now finished reading the slideshow tutorial. Please leave me (nikitakit) a comment about your thoughts concerning this page.

GNU/Linux users may also be interested in AkhIL's imag2sif shell script. It imports images into Synfig and creates a rotate and translate layer for each.

The explanation of the "Straight" blend mode in this tutorial lacks a screenshot. Feel free to add one.