A RAW refresher: the differences between JPEG and RAW.

Started Oct 7, 2012 | Discussions thread
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howardroark
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A RAW refresher: the differences between JPEG and RAW.
Oct 7, 2012

A recent thread on this forum reminded me of a certain way of thinking about digital photography that I honestly thought had died out.  An argument was made about the value of storying digital images in JPEG vs. RAW formats, basically saying that most people don't need to bother with the RAW format.  In the literal interpretation of that argument I have no disagreement:  a vast majority of people buy relatively inexpensive cameras or use their smartphone as a primary photographic tool, and it is that majority of people that should neither be bothered with the hassle of editing nor would they pay much attention to anyone talking about editing technique or fine art in the first place (not having the option of RAW makes it easy to not worrying about editing RAW files).  Posting pics on Facebook or Flickr from the phone doesn't require much precision or care nor is its main focus art or expression of any deep meaning.  They are usually snapshots of people that would most likely be a part of the old fashioned family album.  In that capacity they are still very important and worth recording, but it is the connection to a memory or important event that is the primary focus.  Or perhaps people have simply learned how their camera behaves, what settings they like, and are very happy with the JPEG files it outputs for their intended use, whether that's artistic, professional, or casual.  Different strokes and all that.

For photographers that take pictures for artistic purposes perhaps editing is more important.  I'd argue that even those who have become familiar with editing and how certain file types respond to editing would probably agree that applying that skill is quick and simple enough that even snapshots would benefit from the most flexible set of editing tools possible.  To those of us who shoot for both art and for the fun of taking snapshots I think it's safe to assume we've learned that it's hard to tell when a snapshot will have the unexpected potential to be a great work of art; when a snapshot not perfectly composed or exposed could end up being the shot of your life or possibly just a very important snapshot to go in the album.  In those cases having a RAW file could be important.

I'm not saying that JPEG is useless and RAW is the only thing any sensible human on the planet would use, but I do think people should be aware of the differences so they can make an educated decision.

To remind myself of some of the technical details of how JPEG and RAW files are encoded I went to Luminous Landscape to re-read an article that I read ages ago.

http://www.luminous-landscape.com/tutorials/understanding-series/u-raw-files.shtml

Good, quick refresher.  But the problem was it only discussed 12-bit RAW files and then only split the dynamic range into five stops of dynamic range.  I wanted to see what 14-bit encoding could do and a more realistic representation of current dynamic range.  I ran across the site below that had some very detailed breakdowns of the processes for encoding JPEG and RAW files. The section labeled "Human Vision and Tonal Levels" was very enlightening.  It discusses how the human eye responds to tonal levels in the darker and brighter levels.  As explained in the previous article: "Both the sRGB and Adobe RGB colour spaces use a gamma 2.2 encoding. Gamma encoding reallocates encoding levels from the upper f-stops into the lower f-stops to compensate for the human eye's greater sensitivity to absolute changes in the darker tone range."  The article below shows values for the more common 14-bit A/D converters currently used.

http://www.normankoren.com/digital_tonality.html

Of note after the chart showing how each level breaks down:

A few things are evident from this chart.

  • Levels are lost when converting from a 12-bit RAW format (4096 levels total) to an 8-bit file (8-bit B&W or 24-bit color). But image quality in an 8/24-bit file will be adequate, though just barely, if the exposure is correct and little editing is required. This is achievable in studio environments, but less often when using "natural" (i.e., uncontrolled) light.
  • 16-bit files (16-bit B&W or 48-bit color) have plenty of levels (65,536 total). You can edit to your heart's content without fear of banding or other artifacts arising from limitations of 8-bit files.
  • When RAW conversion is performed within the camera, i.e., when you save JPEG (or other standard) files instead of RAW files, you have little control over the process. The Canon EOS-10D has a contrast setting that gives a small amount of control, but it's awkward to access and it makes little difference.
  • If you save files as RAW (the sensor's native format) and convert them later on a computer, you have enormous control over tones when you convert.

And:

  • If you choose to save images in RAW format, you should expose to capture maximum information: to maintain as much highlight and shadow detail as possible, even if the middle tones aren't what you want in the final print. You should strive to capture all highlights except for bright light sources and specular reflections. You should expose enough to capture detail in large shadow areas. I mostly agree with the Luminous-Landscape.com article, Expose (to the) Right, which recommends setting the exposure to the maximum value that doesn't burn out highlights. (This applies only to images saved in RAW format.) However I wouldn't go too far. A little margin doesn't hurt; there are plenty of levels in 12-bit A-to-D converters. In extreme situations, you may want to make two exposures and combine them. Shadow and highlight detail are extremely important in fine full-toned prints. To my eyes, a print with dead shadows or burnt out highlights looks amateurish. One of the things that distinguished the glorious prints of Paul Strand, Edward Weston, and Ansel Adams is the tonal detail in shadows and highlights, as well as middle tones. If you haven't seen original prints by these great artists, it's time to make a pilgrimage.

A great Adobe white paper on Gamma Correction can be found here:

http://www.adobe.com/digitalimag/pdfs/linear_gamma.pdf?PID=5145718

One useful quote among many was this:

"You may be tempted to underexpose images to avoid blowing out the highlights, but if you do, you’re wasting a lot of the bits the camera can capture, and you’re running a significant risk of introducing noise in the midtones and shadows. If you underexpose in an attempt to hold highlight detail, and then find that you have to open up the shadows in the raw conversion, you have to spread those 64 levels in the darkest stop over a wider tonal range, which exaggerates noise and invites posterization."

Now, to be fair all of these articles were written several years ago (considering they mention the 10D or 12-bit RAW encoding that is no longer common today) and there have been advances in JPEG encoding.  The point is that there are limitations inherent to every method of encoding that can not be undone once processed and saved to your camera's flash memory.  The article below discusses the proprietary aspect of RAW files.

http://www.luminous-landscape.com/essays/raw-flaw.shtml

Almost every manufacturer except for one notable medium-format back maker share their RAW codecs with everyone who wants them.  They may not give away every detail, but viewing and editing RAW files isn't difficult to accomplish.  Also, with the advent of DNG as a universal RAW format and a converter that will allow you to change any existing RAW file into a future-proof and open format for eons to come there's no reason to be afraid of losing support in the future.  If you're worried about it set the converter to work before you go to bed and in the morning you'll have a future-proof archive.

This is not intended as anything personal, but when outdated modes of thought are presented to those in this forum I can't help but attempt to set the record straight.  Having hard data and correct explanations of how digital image files can be very important for pros, amateurs, and enthusiasts learning everything possible alike.  The information presented above does not necessarily invalidate some of the points made in this post http://forums.dpreview.com/forums/post/50005989 but it does refute many technical points that are either factually incorrect or misleading due to lack of a complete explanation.  Even the first comment about underexposing is proven incorrect in the previous articles.

For a long time I believed such claims, but as I learned from reading and from giving RAW a try firsthand they are by and large invalid.  Hard drives are cheap as are flash memory cards, so space isn't much of an issue.  Converters turn your RAW files into a universal, open format if you're really paranoid about that kind of thing.  And if you ever have a file that you want to edit to its maximum potential, RAW is very important to have.  Modern RAW editors have advanced right along with anything that will edit JPEGs or camera processors that will create JPEGs.  And the comment about getting the exposure correct the first try implying one is "lazy" if unable to do so or photographers not being able to do as good a job as a Digic processor are non-starters, especially when the optimum exposure is to the right as opposed to one-stop under exposed.

Exposure is often subjective and open to interpration from an artistic perspective, and editing an optimized file to achieve the proper look of an exposed shot is very easy to learn.  Yes, you can quickly learn how to get more out of a RAW file because you have an editor with tools a camera can't even dream of.....and it doesn't take a computer scientist or Ansel Adams to figure out how to use those tools.  If you can do a good job editing a JPEG you can do an amazing job editing a RAW.  Editing any file to maximum effect will require tight control over monitor calibration and printer control (home or pro labs), but the same is true no matter what you're editing.  The point is getting the best result from what you have and learning how to improve if you want to continue growing as a photographer.

 howardroark's gear list:howardroark's gear list
Canon PowerShot G1 X
Canon EOS 10D
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