What's So Good About RAW?
photographers talk about something called "RAW". Usually accompanying this is some
strange talk about a so-called "digital negative". What's all
this about? What is a RAW file, anyway? Why would
someone use it? These are just a couple of the questions we'll
deal with here.
If you've been around here for a while, you may wonder "What's with all
the digital photography articles, anyway?" Don't worry, I'm not
ditching film. Actually, these articles about digital are going
up here so new readers understand that all this "I love film" talk is
not out of some willful ignorance. In other words, my
choice of film is not because I'm some kind of holdover from the Civil
War or something; instead I've chosen it because I know exactly
what digital has to offer, yet I prefer film anyway. I don't
reject digital completely; in fact it's a great tool for many
things. (You'll see in these articles, hopefully, just how much I
do appreciate digital photography.)
Anyway, let's get on with the topic at hand here.
What's Wrong With JPG?
In most cases, nothing.
We're going to explore the special-use case of landscape
photography. Well, it's not strictly landscapes, but any photo that
has large areas of tone gradient.
Just so you know, I greatly prefer film for landscapes. I even
prefer the look of a grainy 110 color negative to an ultra-crisp Canon
5D Mk III landscape shot, most of the time. That said, my
favorite "serious" landscape medium is either 120 or 4x5 Velvia
film. However, I do bring a digital camera with me, just
because. And so, this is where JPG vs. RAW shooting becomes an
A color image file has three color channels: red, green, and blue
and B). In a JPG file, each color channel has 8 bits of data,
means the number of shades available in each channel is equal to 2
the 8th power. That's 256 shades in each channel. Three
channels times 8 bits per channel yields 24 bits of color. 24
bits is equal to 2 raised to the
which is about 16.7 million colors. In practical terms, that's
enough color to look realistic to the human eye. By the way, most
digital cameras don't yield images with the full 24-bit color
depth. Just to pick out two common ones: according to the
bencharks, the effective JPG color depth on
the Canon 1100D and 650D is only 21.9 bits. That provides only
distinct colors. Well, in theory it should provide the full 24
bits, but chroma noise sort of takes away from that. I still
don't see how a little chroma noise could turn 16.7 million colors into
only 3.9 million, though, but I'm not going to spend this article
criticizing someone's test methods. Maybe some other
time. The point is that whatever the "effective" color depth
of these cameras, the JPG images look just fine if you get the picture
right. I shoot a lot with the 1100D (Rebel T3) and I have no complaints at all about the color depth.
JPG works great for a lot of things, but the one place it's really
lacking is when you try to do a lot of adjustment to an image
file, especially when there are big areas with color gradients. Because there are only at most 24 bits of color
information to begin with, the computer has a hard time filling in
values when you start stretching the color and tone gradients.
Actually, the values aren't there; the histogram gets a
bunch of spaces or gaps in it.
The real-life outcome of this is that your JPG files get "tone banding"
or posterization. Large, graded areas of color, such as blue skies, look
artificial and nasty. The same thing can
happen with any JPG file, even if it's from a scanned slide or
negative. Once a picture gets crammed into the 24-bit color
space, it doesn't have much room to spare for image edits.
Here's a digital photo, shot in JPG, that can illustrate the
point. It was underexposed because, well, I think it looks
cool. The only reason I'd actually want to
image is to compensate for the darkening that happens when you print it
on photo paper. (Photos always look brighter by emitted-light
than they do when printed.)
Mouse-over to see the limitations of JPG.
First version: the JPG as-taken.
Extreme tone banding! This is a little bit exaggerated just to
show you the effect, but even fairly tame curve adjustments can start
to show color zoning.
Poorly-written software makes matters worse. On my old flatbed scanner,
the bundled "film scanning" software was so bad that it caused tone-banding on every scan that had big expanses of sky. Just using different software made a big difference.
Using better software has its limits, though. Even the
best-written software is still going to leave gaps in the histogram
when you do curve adjustments, drastic saturation changes, etc.
Those gaps in the histogram indicate the boundaries of the tone
bands. There is no longer a smooth, natural-looking gradient of
color and tone.
So, what's the answer to this problem? In concept it's very simple: include more colors in the image!
Billions and Trillions of Colors
A TIFF file can have 16 bits per channel, for a total of 48-bit
color. That's not twice the number of colors in a 24-bit JPG
image; it's actually way more. A 24-bit JPG can render
2^24, or about 16.7 million, distinct colors. A 48-bit image file can
render 2^48, or more than 281 trillion distinct colors! A trillion is a million times bigger than a million.
camera manufacturers have designed different "RAW" files to be
able to export somewhere between 16 million and 281 trillion
colors. The upper end of the scale gets into some very
large file sizes. If you think your camera's RAW files are big,
try dealing with a 48-bit TIFF scan of color film, scanned
at the highest dpi setting on the scanner. If it does't
freeze your computer, it'll wear out your hard drive bearings with all
memory swapping. For a while, I got accustomed to dealing with
300-megabyte TIFF images from my film scans, until (believe it or not)
my hard drive
bearings actually did wear out. The reason I scanned files that
big was in the hope that I could archive them until image-editing
software got better. Problem was, my scanner was not that good
(here's a better way to scan film.)
So anyway, full 16-bits-per-channel files are a little bit much.
They're good for archiving pictures (even though CD's and such are not
archival), but for image editing they're actually more than we
need. Cameras seldom even offer the full 16-bits per channel in
their RAW files. The most you'll usually see is 14 bits per
Even though the RAW file is really just the data from each sensor pixel
(which is either red, blue, or green), the output of that file has to
combine the channels to produce a picture that humans can look
at. That's why we often talk about RAW files as if all channels are
combined, as they would be in a JPG or TIFF file (or whichever file type you choose when exporting from RAW).
The point is that when the RAW information is converted into a real
image file, that image file can have up to 281 trillion colors.
It probably has less, because few digital cameras are even capable of
recording a full 16 bits per channel. Nikon "NEF" files, for
example, can have 12 to 14 bits per
channel. With three channels, 12 bits per channel could export an
image having 36
bits of color. 14 bits per channel would yield 42 bits of
color. Remember that the total number of colors rendered equals 2
raised to the number of total bits. Thus, 12-bit RAW files (being
able to output up to 36 bits total) could yield a picture having up to
2^36 colors, or about 68.7 billion colors. 14-bit RAW files
(having 42 bits
total) would offer images having up to about 4.4 trillion colors.
The output from a 14-bit RAW file has up to 64 times more colors than
the output of a 12-bit RAW file. That's a lot of colors.
Anyway, a RAW file that has 12 bits per channel is still a lot better
than a JPG file that has only 8 bits per channel. An output
file having 68.7 billion colors is obviously going to be much better
than a JPG having only 16.7 million colors.
Hey, wait a second! If we know the human eye can differentiate only 4 to 16
million colors, then why would we need RAW files anyway?
The reason, again, is that if there are more
colors, you can do more substantial image edits without causing tone bands and
other unsightly artifacts.
the way, I've said before that megapixels are overrated.
That's generally true. However, one advantage of having
more pixels crammed onto a sensor is that curve adjustments are less
likely to yield tone banding. In the extreme, picture a sensor
that had only 1,000 pixels on it. There aren't even enough pixels
to represent the tone gradient of a sky. If you adjust the
curves, adjacent pixels are going to have more drastic differences
between them. Now consider a sensor with ten million
pixels. This will be more able to display a good tone gradient,
even when you start adjusting the curves. I haven't sat down and
figured out how much this effect contributes, but once you get past
(say) 10 megapixels, the color depth is probably more important than
how many pixels.
Once you have the ability to make drastic tone & color adjustments on a photo without tone-banding,
you can then "develop" underexposed pictures to your
liking. As you might remember from Camera vs. Log,
digital does very poorly with highlights, but it happens to do well with shadow detail. Shooting in RAW and
underexposing is the best way to handle this. Then, your "developing" can turn into
a chore that's even more time-consuming than scanning film. Welcome to the club!
Ken Rockwell calls film "the real RAW", and he's right. Film has,
in theory, practically an infinite range of color and tone
values. In practice the number is limited (temporarily) only by the method we
use to digitize it. 281 trillion colors is within reach, if
you scan as 48-bit TIFF (i.e., 16 bits per channel). Film
also has that beautiful, deep tonality to begin with. Speaking of which, the tonality of film is more than simply a
result of color depth. I say that because, even in a scan that has
only 16 million colors, the film scan JPG looks richer than a JPG made on a
digital camera. There are probably at least a couple of reasons for this.
Anyway, if you can
scan negatives or slides in 48-bit TIFF, there's enough color and tone
information that it can sort of act as a "digital negative". In
fact, that's exactly what many people call these files. (Save the
and negatives, though..... "digital negatives" are not truly archival, and they're nowhere near as information-rich as film.)
Ken is right about something else, too. Most of the time you can just shoot in JPG,
if you know what you're doing. I know a lot of people who
do this. I usually do this. Actually just the other day (before I wrote this) I was talking to a
portrait pro who said she never shoots RAW. It just so
she's also been shooting film for many years.
Hmm, I see a pattern here.
We've seen that JPG has some limitations, and we've also seen that
don't care. Why choose RAW? Well, it depends on your choice
of subject and shooting conditions. For pictures with a lot of
sky in them, RAW is a
much better idea, especially if you have to underexpose to avoid
clipping the highlights (such as cloud detail). Even
if you do get the exposure right, I've found that saturation
adjustments on a JPG can cause tone-banding anyway.
Why is JPG sufficient for most everything else? Experienced photographers
work to get the exposure right the first time, and if they can't, the
"keeper" is probably in one of their two bracket
shots. JPG is viable there. Of
course, since JPG takes up less space on the memory card and writes a
lot faster, it's easier to make those bracket shots. I like
shooting RAW for sunsets and skies, but waiting for these massive files
to write to a memory card is not exactly fun when you're trying to
shoot action sports. (On a side note, my old bridge camera at a
wedding reception was probably slower than if I'd brought a Crown
Graphic 4x5 with flash bulbs. f/8 and be there!)
Formulating a Workflow
The "workflow" is the series of operations you do on pictures to make
them look the way you want. It could also include getting the
pictures ready for a printing process of some kind. Thus,
you could have a RAW workflow, a JPG workflow, or one that incorporates
both at different stages. (Just to nitpick: There's no actual
"RAW" workflow, technically, because as soon as you export that sensor
data to a human-viewable image, it's not RAW anymore. Common file
types are TIFF or PNG, if you want the 48-bit color depth).
The workflow should be designed to preserve the maximum quality, while
not being ridiculous. There are some editing operations
that don't actually need to be done on a 300-MB TIFF file. (Glad
of it, too... and so are my hard drive bearings...)
There's one more thing I'd point out here. Just because you have
a program that can edit TIFF or imported RAW files, that doesn't mean that
program will do the best job on the image. In fact, it doesn't
even mean that program will do as well as some other program that only
works on JPG files! The reason I say that is because I was using
a certain program, and I noticed it had its own
algorithm. So I tried that, and I found that not only was there
too much detail loss, but there was also.... tone banding!!
Arghh! I think I said it before, but:
Poorly-written software or algorithms can introduce digital artifacts
into your picture.
Learn which functions of your favorite programs are the least
destructive to your photo quality. The "tone curves" setting in your RAW
editor might be pretty good, but some other function might be very
sloppy and ruin the picture. In the example I mentioned above, I
found that I could adjust tone curves, saturation, and levels without
too much problem, but most of the other functions are probably better
off being done after exporting to JPG and opening the picture in some
other program. That's part of how you develop a workflow that works.
What's the bottom line here? JPG is good enough for most
stuff; RAW is great for landscapes and such. (For your main
This has been a look at JPG vs. RAW. I hope you've found it helpful! You can help me out by shopping for your stuff through the links or banners on here.
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