Cfrgtkky

Many digital cameras use lossless compression with raw files. That means the size of raw files from the same camera is somewhat content dependent.

The more detail and different colors a scene contains, the larger the file will be. The more homogeneity a scene contains, the smaller the file will be. The degree of the differences will also be governed by differences in things such as noise in dark areas (noise usually adds to a file size by creating a greater number of unique brightness levels).

A picture being worth a thousand spreadsheet cells, here is an histogram of the size of the RAW files from my camera for 2018 (EOS 70D, 20Mpx). Sizes are in 1000's of K (not really MB).

For the mathematically inclined:

Average:    24538

Median:     24300   

Std dev.:    2119

A little extra info: If the raw file includes a preview (they generally do) that's likely to be jpeg compressed and will cause a small variation in file size.

Checking some raw CR2 files I shot yesterday (I keep an old Canon 350D in my desk), 3 shots of essentially the same scene vary by about 3%. I was fiddling with the lighting and used a very black background so one has both blown highlights and (almost) pure black, both of which compress well even losslessly.

However in terms of load balancing you're probably fine: averaged over a sensible number of images the load will be sufficiently similar unless your system is right on the edge, and transfer- or decompression-limited.

There are two main types of compression methods:

1. lossless compression


2. lossy compression

As you mentioned, JPEG is a lossy compression method which uses some mathematical tricks to save data, therefore losing picture information resulting in quality loss.

Basically, if you save a picture and store the color information for every pixel without any encoding, then every picture would most likely be exactly the same size.

But as there exist lossless compression methods, you have the ability to save file size without losing any quality. The most basic example would be Run-length encoding where you can combine identical successive information and thus save the space you would need to store them one by one. For example you would store the information like "2 white, 3 black" instead of saying "white, white, black, black, black".

This results in pictures without much variance being compressed to relatively small file sizes, while this is not possible for those with a lot of variance in them.

This is why different raw pictures taken on the same camera will most likely result in different file sizes.

This may be camera-dependent, but for my Canon EOS 7D Mark II, different raw images are definitely not the same size:

# ls -l *.cr2

-rwx------ 1 tew tew 23868042 Jan 21 10:59 20190121105920-6996.cr2

-rwx------ 1 tew tew 24408037 Jan 21 11:07 20190121110757-7002.cr2

-rwx------ 1 tew tew 25928707 Jan 21 11:08 20190121110823-7003.cr2

-rwx------ 1 tew tew 23777211 Jan 21 11:08 20190121110852-7004.cr2

-rwx------ 1 tew tew 25369539 Jan 21 11:09 20190121110922-7005.cr2

-rwx------ 1 tew tew 22675822 Jan 21 11:11 20190121111113-7006.cr2

-rwx------ 1 tew tew 23377077 Jan 21 11:11 20190121111119-7007.cr2

They are all pretty close in size, but there's definitely some variance, which is primarily due to compression of the raw sensor data as well as the metadata and embedded JPG preview image.

Now, in case you are also interested in less popular brands, here is how Sony handles RAWs.

Currently used RAW files (file extension ".ARW") come in 2 types: 8 bits per pixel (called "Compressed RAW") and 16 bits per pixel ("Uncompressed RAW"). Some cameras are limited to 8 bit, the high end cameras can write either type.

Consequently, all RAW files from a given camera are nearly the same size, equal to the number of megapixels (for 8 bits) or twice the megapixel count (for 16 bits). Actual file sizes fluctuate a bit because of the embedded JPEG preview but the RAW data itself is always constant size.

Raw files potentially have the exact same size, but in practice, they almost always don't. Reasons include:

• Variable size of metadata. (twalberg)


• Variable size of JPEG preview thumbnails. (Chris H, szulat)


• Lossless compression. (Michael C, sLaiN)


• Lossy compression. (sLaiN)


• Reduced resolution raw files.


• Reduced bit-depth raw files.

Without knowing exactly what devices you are using, it is impossible to directly and accurately answer your question.

• Canon – CR2 files are losslessly compressed. (Chris H, twalberg, xenoid)


• FujiFilm X-Series – Cameras using G1/G2 X-Trans sensors (16mp) and Faux-X Bayer sensors do not use compression for raw data. G3 and later X-Trans sensors (24mp) have the option to use lossless compression.


• Nikon – ???


• Olympus – ???


• Panasonic – ???


• Pentax – ???


• Sony – (szulat)