Are all the RAW files the same?

Question

I have an android phone that is able to take the photos on RAW mode. Would it contain the same information as a DSLR camera? That brings another question, do the raw photos from all the DSLR cameras contains the same data?

Answer 1

In short, a "raw" file is kind of like a book. Most all books contain ink on paper. But how many pages, what type of paper, the size of each page, how it is bound, what kind of cover, what type(s) of ink, how the columns are arranged and formated, what language(s) are used, what font(s) are used, whether it has a table of contents, an index, a bibliography, etc. can and often will vary greatly from one book to the next.

How much and what kinds of information a raw image file contains and how that information is arranged can also vary greatly from one camera to the next.

All photos taken with digital cameras are based on raw image data collected using a silicon based imaging sensor. That's pretty much where the similarities between all conceivable types of digital imaging device ends.

A "raw" image file is not a file format in the same way that a JPEG or PNG file is. The word "raw' is used to describe information digitally stored in a data file that was gathered using an imaging sensor with minimal processing applied before the analog readings from each sensel are converted to digital information.

There are various ways that the actual analog voltages measured by each sensel (a/k/a pixel, pixel well, photosite, etc.) on an imaging sensor are processed and amplified before being converted to digital information.

There are various file formats used to store that digital information. Many of those different file formats use similar containers to hold the data.

Most camera makers have their own proprietary raw file formats. Nikon uses .NEF files to store raw image data and the attached EXIF info and preview images. Canon uses .CR2 (or the older .CRW for some of the earliest digital models). Other camera makers are similar. There are currently over twenty-five different "raw" file formats listed at the Wikipedia entry for Raw Image Format. There are at least three different types of "raw" image files that use the .raw file extension!

Many "raw" file formats are based upon the .TIFF file format, but they all use that format differently to contain the raw image data. From the Wikipedia entry:

Many raw file formats, including IIQ (Phase One), 3FR (Hasselblad), DCR, K25, KDC (Kodak), CRW CR2 CR3 (Canon), ERF (Epson), MEF (Mamiya), MOS (Leaf), NEF (Nikon), ORF (Olympus), PEF (Pentax), RW2 (Panasonic) and ARW, SRF, SR2 (Sony), are based on the TIFF file format. These files may deviate from the TIFF standard in a number of ways, including the use of a non-standard file header, the inclusion of additional image tags and the encryption of some of the tagged data.

But even among different cameras from the same manufacturer that use the same file extension, if they use different sensors then the applications that interpret the "raw" data must have information about how the "raw" data from that specific sensor should be processed. A .CR2 file from a Canon EOS 7D Mark II should not be processed by the same algorithms that a .CR2 file from a Canon EOS 5D Mark IV should. An .NEF from a Nikon D500 should not be processed the same as an .NEF from a Nikon D810. And so on.

Some raw file formats preserve more of the information gathered by the image sensor, as well as other data about the camera and selected settings at the time the image was captured, than others do. For instance, the Canon .cr2 format preserves the actual measurements taken by masked pixels used to help set black point and determine image noise caused by thermal factors. So do many other cameras. This allows the black point to be set to a different value during external raw image processing. But there are also cameras that go ahead and calculate the black point and apply it to the raw data from each sensel before it is recorded and then discard the information from any masked sensels. This "bakes in" the black point. Many camera makers include additional, non-standard metadata in the 'maker notes' section of the EXIF metadata. Image processing software may or may not use some or all of the 'maker notes' information. Adobe products, for instance, ignore most of it and even strip it out of raw image files when they are converted to the Adobe .DNG format!