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(Pocket-lint) - The most fiercely fought of battles when it comes to smartphones is in camera performance. It's the first port of call when it comes to comparisons, it's where the fans compete and contrast their devices.

Smartphone cameras have been getting more sophisticated and one of the recent additions is raw capture. It's something that camera fans will be all too familiar with, but what is it, and do you really need it on your smartphone?

We'll guide you through what it is, how it works and whether it's worth it, so read on.

What is raw?

Raw (sometimes referred to as RAW) is the actual data captured by the camera sensor. Raw is sometimes called a digital negative, alikening it to film cameras. 

When you capture an image with a digital camera (be that a smartphone, compact camera or DSLR), the raw data from the sensor is processed before it is presented and saved as a final JPEG. At the same time, raw files are usually presented with JPEG thumbnails, so your thumbnail usually doesn't match the raw file exactly.

It's that unsullied data in its original form that's called raw. There are different raw formats, the common universal type is DNG and that's what you'll likely get from a smartphone, but manufacturers like Canon and Nikon use their own (CR2 and NEF, respectively).

Why shoot in raw?

The advantage that raw offers is that you get access to that original data, rather than just the JPEG that's been processed. JPEG files are usually compressed for convenience so a lot of data is lost at that time. Using raw gives you access to all that data before anything happens.

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The advantage is that you can then make wider decisions about the processing you can make to your file, as the raw file has data in areas such as shadows, or in highlights, that the JPEG loses during compression.

Many pro and enthusiast photographers choose to shoot in raw because it gives more options when it comes to finalising the image you'll use and gives you the chance to correct things that the settings on the camera might have got wrong, such as the colour temperature.

In raw files you can make wide changes to the exposure, the white balance, shadow depth, highlights, black levels, white levels, saturation and more, and in many cases you can do so without having a detrimental effect on the rest of the image, which isn't the case with JPEG processing. 

Why not shoot in raw?

Principally, because of the size. The data that comes from the sensor is probably around the 20-30MB mark in raw form, whereas the compressed JPEG is maybe 3 or 4MB. This depends on the size of the sensor and how many pixels of data you capture.

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Not only does that raw file take a lot of storage space, but any processing you might want to do on it needs power. Nothing like the sort of power needed to crunch through video, but it's still a demanding task given all the processing options you have. It's also a highly visual process, so much better suited to a computer than a small smartphone display, as are the controls for the sorts of tools you often use to do the job.

Then you need something to process the raw files. Applications like Photoshop or Lightroom are common (and expensive), while Gimp is a popular alternative on a desktop. We also use Photoshop Elements, which has basic but powerful processing tools.

There are apps to process raw images on a phone or tablet, but they often cost and, thanks to the small display, it's going to be a fiddly process rather than a nice smooth workflow. Arguably, however, with the advent of devices like the Microsoft Surface, the line between tablet and laptop is blurring, but there's a big difference between your Android smartphone and your MacBook Air.

But isn't the camera/smartphone processing raw anyway?

Yes it is. When you take a shot, the image is processed and a JPEG is produced, using a range of pre-set values. In many cases, the raw and JPEG are saved together, so you can instantly share one, then perhaps tweak it if you think it could be better later on. This is separate from common JPEG image editing tools that are offered on most smartphones.

In a lot of cases the raw file won't look as good as the processed JPEG, so some of those pre-set processes include corrections for things like lens distortion or imperfections. Many of these things you won't see, but it's here that manufacturers can tweak how the output looks - for example increasing the saturation perhaps for bluer skies, processing away high ISO noise for a smoother finish in low light and so on. 

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This is where access to raw files gets interesting, because you can see what the manufacturer is doing to try and produce the best final image in a smartphone. 

What smartphones offer raw capture?

Nokia was one of the first manufacturers to offer raw capture, aiming to bolster the armoury of skills that the Lumia 1020 offered through the Lumia Black update. Subsequently we've seen others offering raw capture, like OnePlus One.

In more recent times we've seen HTC add raw to the One M9 and Samsung has been talking about its introduction with Android 5.1.1 on Galaxy models. We've been playing with raw capture on the HTC One M9 and used it for the examples below.

In some ways, raw has become the thing to add to be seen to be progressing your camera, even if, in reality, the vast majority of users use the default auto mode and that's about it.

Smartphone raw samples

We can't embed a raw file here, so we've created a JPEG with no processing. This gives you can idea of what the sensor is actually capturing, compared to the processing that goes into a JPEG.

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The immediate and obvious difference is the vignette. The centre of the raw image is lighter than the edges. In the JPEG the smartphone produces, this is levelled out for a more even exposure across the image. 

At the same time, you'll notice that the colouration changes. The raw is closer to the actual scene in real life, but after processing in the phone, there's a slight green-yellow tinge, especially noticable in the blue of the sky (typical of the HTC One M9 camera). Elsewhere you can see the sharpening to put some texture back into those trees.

Flip to something that's much darker, and again we see the same characteristics. The centre of this night shot is lighter than the edges. It's skewed in the image in our gallery, because of the streetlight illuminating from the right-hand side, but evident on the left.

When this is processed into a JPEG by the smartphone, we can see added noise appearing in the sky, which is noticeable immediately. The processing evens the frame and adds that sharpening again for a final image that is perhaps a little more processed than you'd want it to be. 

In an ideal world, the raw from the smartphone would let you tweak these colours yourself, but the biggest barrier is the unevenness across the frame. Unlike the raw files you'll get from a DSLR with better optics, these raw files from the HTC One M9 are more difficult to post-process and need a lot more work.

It's worth noting that the raw capture on the HTC One M9 shares the UI with the manual camera, so you get to set the ISO, shutter speed and so on. We used a 2 second exposure to create those light trails from a passing car.

Is raw in a smartphone worth it?

We're fans of raw shooting. Even for the most basic of photography tasks, having the option to change something like the shadow weight or white balance without destroying the image is really handy. But we're also fans of shoot and share photography a smartphone offers. Both have merits but the use cases are different in many ways. 

We always have a phone and we use the camera a lot. Things have come along leaps and bounds in the last few years. In good light, a shot from the iPhone 6 or Samsung Galaxy S6 is really very good, but if you know that quality is important, you can't beat a proper camera, with a proper lens. In most situations we use a DSLR, because you're going to have quality and depth that a smartphone can't match, especially if you're cropping in and displaying large.

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Yes, the cheap end of the compact camera market can't compete with the convenience of a smartphone any more. But once you add in raw shooting and the need to then process those files on a PC before you can do anything with them, then we question why you'd then compromise on a smartphone, when you could use a camera that's going to be better photographically in almost all areas. 

We'd urge camera users to experiment with raw and see just what it can do, but for a smartphone we are less enthusiastic. If you think that a smartphone is going to give you enough quality then fine, but the need for somewhere to carry out the processing after the fact negates the smartphone's primary appeal and you might as well use a camera.

Offering raw isn't the final position for smartphones. Giving the user the power to really tweak what's happening, perhaps to adapt some of the elements of the camera they don't like, is more useful to a power smartphone user. But ultimately, offering great auto shots with no intervention, so they can be instantly shared remains the big attraction of smartphone photography.

Writing by Chris Hall.