File Size in Animations
Animations can vary in file sizes and this is completely dependent on the content of the animation. An animation with more colours, frames per second and length will be larger in size thus taking longer to load on the internet. These animations would be of high quality at the cost of high file size. Lower quality animations would be lower in file size.
Frame Disposal
Frame disposal is a method used in animations for the reduction in its file size. Frame disposal simply removes the current frame before the next frame is brought up, so the two are not existent at once which makes for the lower file size each time a new frame is introduced - it is removing unnecessary frames. The obvious benefits are that it reduces file size, can make the animation smoother and might even improve the animation by reducing the number of repeated images/frames in an animation. However frame disposal could lose some of the animation's content as it's getting rid of some frames.
The image above shows options of frame disposal. The automatic option will remove a frame if the coming frame has layer transparency. 'Do not dispose' disables disposal in the frames, and 'Dispose' will dispose of the frame regardless. Adobe have a guide on animations here.
The two animations above are made differently, with transparent backgrounds. The first image is made with the 'Dispose' option, while the second is made with 'Do not dispose'. This is evident as the previous frames are still present during movement, while in the first one the previous frame is removed as the second one comes on. In an animation with a background this is not an issue as it is in the second animation, however due to the transparent background it does not appear well and would require the dispose option.
Auto Crop
Auto crop is a feature present in many programs and is used to clear the blank space on the canvas in order to decrease file size and reduce/remove unnecessary space. It simply crops down to the furthest edges of the drawings to remove blank space wherever it can. The image below is a cropped version of the image above. The tool used here was the Trim tool, highlighted in the Image menu. This allows one to base the trim off whichever pixel (I based it off the bottom left, which was white). It cropped accurately to the edges.
Other Factors Affecting File Sizes
Colour Depth/Number of Colours
More colours in an animation will obviously increase its file size. This is because more colours are stored and represented in the animation. Simple animations featuring fewer colours will load much faster and can afford to be longer because of the fewer colours. It is a matter of balance. Reducing colour will take a drastic hit on the quality but also on the file size, thus making it easier to load.
Transparency
Background transparency in an animation can reduce file size. This is because there aren't extra pixels present for the background - without these extra pixels the image reduces slightly in file size, and transparent animations are preferred usually over ones with default backgrounds because they take on the background of the site itself and it looks well blended in and fitting.
Sounds
Sounds in animations are not always common but it goes without saying that including them into an animation will boost the file size. Higher quality sounds will make the animation even larger.
Resolution
Better resolutions for animations will make the file much larger which can be worth it for the noticeable quality. However resolution might need to be sacrificed for a lower file size, and sometimes it would need to be reduced anyway for mobile devices because high resolution images could be larger and thus being unable to fit properly on a phone screen.
Frame Rate
This is very simple - higher frame rate means more frames in a second, meaning more loading due to the file size. Higher frame rates deliver better quality and smooth animations, but with this comes longer loading times with the large file size. Reducing frame rate is the obvious solution, along with others offered by some sites such as skipping every 5th frame for example, it will give a choppier animation but will be lower in file size.
Content
After numerous attempts at compression an animation might not be accepted by some sites (for example a site might only accept 5MB or lower animations). Some of the content might have to be cut from the animation or one could reduce some frames as mentioned above for a choppier performance but enough for it to be uploaded/used properly.
