The fade-out effect is a very subtle way of transitioning from one image to another whether in slideshows. Most would use slideshow applications with fade-out effects but you can also achieve these effects with GIF animations which does not require any plug-ins for it to be played on your browser. You can create GIF animations with most graphic software, such as GIMP which is a freely distributed imaging program comparable to Photoshop.
It’s important to note that as much as GIF files allow transparency in your images, it is not always the case for GIF animations. In creating fade-out effects, one might think merely of adjusting the opacity or transparency of the image at your GIF animation file which, in my case, gave me fully opaque frames of the top image, never showing the lower level images despite opacity adjustments.
To really achieve the fade-out effect, you will need two GIMP files : one working file in which you can adjust the opacity of the images, then copy the visible image to a second file which serves as your GIF animation frame. At your GIF animation file, each frame should be the combination of two images where the top image is slowy fading letting the lower image show through.
First, open your image files with GIMP and make sure all of them have the same dimensions for uniformity. You can crop out large images using the Rectangle Select tool to highlight the part of the image you want to retain. The expanse of your Rectangle selection can be seen at the bottom part of your GIMP window whenever you’re adjusting the selection with its arrow guides. At the menu bar, click IMAGE->CROP TO SELECTION to crop out the rest of the image.
Now, put all of your images in one working file by clicking EDIT->COPY then EDIT->PASTE AS->NEW IMAGE at your first slideshow image which automatically creates a new working file. For the other image files, click EDIT->COPY then EDIT->PASTE AS->NEW LAYER at the file created by the first slideshow image. At this point, you can close the photo images discarding the changes you’ve made to the file. Arrange the images using the Up and Down arrows at the bottom of the Layers dock.
For your first slideshow transition, make only the first two slides visible by clicking the eye icon of the other layers or images to toggle their visibility. Only the first two slides should have the eye icon thus making them the only visible images. Now, go to the first slide and lessen the opacity by 10% or 20%. This should make the lower image slightly show through. At the menu bar, click EDIT->COPY VISIBLE then EDIT->PASTE AS->NEW IMAGE which will automatically open a new window that will also serves as your GIF animation file.
Now go back to your working file and lessen the opacity of the top layer again by 10% to 20%, depending on your preference. Once the opacity is adjusted, click EDIT->COPY VISIBLE then go to the second window at your GIF animation file then click EDIT->PASTE AS NEW LAYER. You should now have two frames for your animation which you can preview the animation, by clicking FILTERS->ANIMATION->PLAYBACK at the GIF file menu bar. Repeat the same steps above until you’ve reached the zero opacity for the first slide image.
For your second slide transition, go to your working and untoggle the eye icon or visibility of the first slide image. Make the third slide visible by clicking the box where the eye icon should be. This should make only your second and third slide visible. Repeat the same steps from the top wherein we adjusted the opacity by a certain percentage then click EDIT->COPY VISIBLE at the working file menu bar. Go to the animation file and click EDIT->PASTE AS->NEW LAYER. Repeat the same steps until you’re finished with all of your slides.
Once you’re finished, save this file with a GIF extension then choose the Save As Animation option at the next dialog box. You can adjust the speed of the animation by specifying the millisecond value at another pop-up dialog. You might want to make the main photo slides to show for a longer time than the transition effects. You can do this by opening your newly saved GIF file. Right-click on your selected frames then click EDIT LAYER ATTRIBUTES and change the number before the millisecond(ms) unit.