What is Lossy Compression?

What is lossy compression?

If you’ve ever tried to send an email attachment that was too large, then learning about compression can make your life much easier!
Some types of media file formats are “lossy”, while others are “lossless”. Below, we’ll explain what the terms mean and the advantages of each.   

Compression, Explained

We use compression to make files smaller, so that they take up less storage space and can be downloaded more quickly. For example, when you take a photo, your camera captures light with its sensor and produces a digital image. If you save the image in RAW format — which keeps all of the light data your camera’s sensor received — then your photo may end up as large as 40 MB, depending on the resolution. Files that large can be very unwieldy.
If you’re uploading these large, uncompressed images to a website or attaching them to an email, you may run into problems. A gallery of RAW images can take up hundreds of megabytes of space, which is definitely too large to send over email. Professional photographers prefer to shoot RAW images, but they’re not always ideal for the average user.
Instead, our cameras and smartphones can also record images as JPEG files. JPEGs are much, much smaller than RAW files. This is because some of the image is “thrown out” when the JPEG is saved. This results in a much smaller file, one that we call “compressed”. If done properly, the resulting JPEG can still look great, though you may see compression artifacts, like blurring or pixilation. 

Lossless vs. Lossy Formats

RAW is a lossless format because it preserves all of the file’s original data. On the other hand, JPEG is considered a lossy format because some data is lost in the compression process.
However, RAW and JPEG aren’t the only lossless and lossy formats. Below are some common file formats for images, audio, and video.

  • Images: RAW, BMP, and PNG are all lossless image formats. JPEG and GIF are lossy image formats.
  • Audio: FLAC and WAV are lossless audio formats. MP3 and MP4 are lossy audio formats.
  • Video: There are only a few lossless video formats available to consumers, and some of the most popular are MKV and WMV.

Lossy Compression

Lossy compression is useful because of its ability to shrink a file to a more convenient size. In essence, it removes bits of information that are harder to see, or less obvious to the viewer.  
Many of today’s cameras have multiple quality settings for saving your photos as JPEGs. As a general rule of thumb, using a lower quality setting will result in a smaller JPEG file, while using a higher quality setting will result in a larger JPEG. If lossy compression is done well, you won’t notice a huge change, but the file size will be significantly reduced.
Lastly, if you decide to shoot in JPEG format, you cannot convert the JPEG file back into an uncompressed RAW file. You’ll be stuck with your camera’s “reinterpretation” of the original data.

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