Image File Formats used in Digital Signage (and when to Use Them)
The first thing that you need to know is that files can either be compressed or uncompressed. Compression "repackages" a file in order to cut down on its file size. We want our digital signage to look good, right? Unless you're hurting for storage space, or you're using digital signage hardware and software that either can't handle large files or only allow the usage of compressed file types, there's no need to use compressed image files. Compressed video files can be a different story; we'll talk about that in a future video file format post.
GIF (.gif) - Graphic Interchange Format
These compressed files should be avoided in digital signage; they are primarily used for the web as banners or small animations. GIF files have a limit of 256 colors, so if you use them in your digital signage it may end up looking like you just pulled something off of the web. This isn't PowerPoint afterall, this is digital signage. The same picture saved in JPEG format will not only look better, but it will also be a smaller file size. If you need transparency, which GIF supports, I recommend using PNG files.
JPEG (.jpeg) - Joint Photographic Experts Group
These compressed files are a widely-accepted, compressed file type. So long as they are not too heavily compressed, they'll probably look good and have reasonably small file sizes. The drawback is that they don't support transparency, so you'll need to mask something over them unless you like plain rectangular images in your digital signage. JPEGs handle photographic images best; don't try to work text or logos into your JPEGs and they'll probably look fine. If you have the storage space, use BMP instead.
PNG (.png) - Portable Network Graphics
My personal favorite. Not only do PNG's look good, but they also support transparency. By using transparency, your digital signage can have organic graphic overlaps that look much more interesting than standard rectangular images. PNG's will automatically assign transparency where there is no pixel information, saving you from having to worry about alpha channels. If you like having some control over alpha channels, or PNGs aren't coming out how you need them to, I recommend using TARGA files. If you don't need transparency, use BMP or JPEG depending on how much file size you have available.
TARGA (.tga) - Truevision Advanced Raster Graphics Adapter
While the file size is larger than PNG format, TARGA allows you a greater level of control over your alpha channels and transparency. This is handy if you work in Photoshop or other editing software, but chances are, you won't need to use this file type if PNGs are working well for you. PNGs are smaller and normally look quite nice.
BMP (.bmp) - Bit Map Picture
This uncompressed file type, while much larger in size than a JPEG file, will always look better than it's compressed JPEG counterpart. If at all possible, use this file type for your images not requiring transparency.
TIFF (.tif or .tiff) - Tagged Image File Format
TIFF files are unique uncompressed files, because a user can actually save layers inside of one. This allows a designer to open a TIFF file later and continue editing where he or she left off. Like Targa files, you probably won't ever need to use them.
To recap, if media storage space is not an issue use BMPs for images not requiring transparency. If you have limited storage space, use JPEGs for images not requiring transparency. For all images requiring transparency, I recommend using PNGs.
There are, of course, several other types of image file formats, but the ones listed above are the most common in the digital signage world. If you have any questions, including questions about file formats not mentioned above, feel free to ask!
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