As the megapixel values of our DSLRs increases every year, we create larger and larger data files that slow us down and give us a storage headache. Yet the data of our digital pictures can be miraculously shrunk using a compression format such as JPEG.
Compression is not to be feared, and is a good thing so long as you control it carefully throughout your shooting, editing and output workflows. If you want to make your workflow leaner and more efficient, read the following advice on how to get the best out of your files.
What exactly is compression?
JPEG compression breaks fine details into blocks and makes later editing near impossible. The JPEG compression routine never changes the pixel dimensions of your image file as data only describes the colour value of each pixel block, not its size.
Pixel size is always fluid and user-defined, and can be set in-camera as 300ppi (pixels per inch), or reset in image-editing software to a different value such as 240ppi or 72ppi.
So, if you’re shooting with a top-of-the-range camera such as the Nikon D810, and making enormous 7,360×4,912-pixel images, they will retain the same dimensions whether you shoot JPEG or raw. They will also have the same potential to be printed at maximum size.
The JPEG routine was developed by the Joint Photographic Experts Group and involves a clever algorithm that reduces the need for a discreet bit of code to recreate each colour pixel. Instead, areas of the image are grouped into 8×8 blocks that are then recoded using less data.
JPEGs can be created with enormous savings at one extreme, or roughly halved in size at the other. The key, however, lies in knowing how much you can squeeze your files before you start to lose image quality.
Poor-quality JPEGs are simply the result of careless workflow.
Extreme damage is caused by repeatedly saving low-quality JPEGs, visible as blocky patterns that cannot be removed easily. This damage looks like a crude pattern of disjointed blocks appearing in previously detailed areas in your image.
Like the compressed MP3 music format, low and medium-quality JPEGs can also feel washed out and lack punch.
Shrinking digital data with JPEGs gives smaller files and makes uploading faster. Shooting JPEGs also allows you to make a longer burst of continuous shots as the camera’s internal buffer does not fill up as quickly as it would if you were shooting raw files.
In practice this is very useful, so if you are shooting fast-moving action on a DSLR such as the Nikon D750, its buffer can hold 87 Fine Quality JPEGs compared to only 15 14-bit raw files.
Unlike other file formats, JPEGs vary in data size depending on the kind of image that you shoot.
Generally, subjects that have multiple colours with sharply focused edges and details need more data than softly focused images with fewer colours. In practice, the former could be 5MB and the latter less than 1MB in size.
Despite such drastic data savings, high-quality JPEGs are an ideal format to shoot with, where the benefits easily outweigh the disadvantages.
If you have been shooting 100MB raw files with your DSLR, then you can easily shoot and store the same image as a 20MB JPEG.
Finally, just like raw files, JPEGs can carry metadata and a colour profile of your choice, so there’s plenty to shout about.