Reduced-resolution RAW image files

June 25, 2013

The new small RAW options have the potential to save a lot of hard drive storage space over time.
This article was originally published on March 28, 2011 and has been updated to include current product information.

Starting with the EOS 50D and EOS 5D Mark II of 2008, mid-range and high-end Canon EOS Digital SLR cameras share a feature that’s been frequently requested by experienced photographers: the ability to shoot RAW image files at reduced pixel resolutions. The so-called “small” RAW image quality option provides all the flexibility that RAW file processing has always given, but in reduced resolution files. With the ability of most EOS cameras to approach or exceed 20 million pixels, small RAW images become an intriguing option that enthusiasts and professionals alike may want to experiment with.

To take advantage of the reduced-resolution RAW file capability we’re discussing here, you need a camera like the EOS 50D/60D or higher in the product line. EOS Rebel models can certainly shoot RAW images, but only at full resolution (this reduced-resolution RAW capability is one of the features you get as you move higher up in the Canon EOS line).

What are the benefits of shooting RAW images?

RAW images are an invaluable safety net for photographers at any level. Since the image is not processed into a finished file in-camera, the photographer has total control over many aspects of how the finished image will look after processing in the computer. Most importantly, RAW images allow the user to totally change various picture-related camera settings when the image is processed. Using a RAW image conversion program like Canon’s Digital Photo Professional (packaged with every EOS cameras), you can completely override settings such as white balance, picture style, tonal curve, contrast, saturation, sharpness and so on. Images can even be intentionally lightened or darkened by up to two full stops. For years, advanced amateurs and pros have relied on the flexibility of RAW images to make creative changes and, perhaps even more importantly, for its ability to bail them out of mistakes in exposure or white balance.

Why shoot RAW files at reduced resolutions?

Most digital SLRs can only shoot RAW images at full resolution. This means using all the pixels on the camera’s imaging sensor, which can mean very large files. With the 22.1 million pixel sensor on the EOS 5D Mark III, for example, each click of the shutter (at full-resolution RAW) writes about a 27 MB file onto your CF card. When that file is processed and brought into an image-editing program like Adobe Photoshop™, by default, it opens up as about a 63 MB file and over 126 MB if you save it in the 16-bit per channel mode to preserve the inherent full bit-depth of the image.

Think about it: if you processed and saved finished 16-bit .TIF images (at full resolution) onto 4.7GB DVDs for a client, you’d completely fill a DVD with only 36 processed RAW images. With today's digital cameras, it's not uncommon for an advanced amateur or professional to shoot hundreds to thousands of images per assignment. Particularly with high-resolution cameras, that means a never-ending quest for space to store original files and finished images.

Full-resolution RAW files are still necessary in some situations. A commercial photographer shooting images for a double-page advertising spread or a fine-art photographer expecting to make poster-size prints of a detailed landscape are two common examples.

However, not all professional applications require full-resolution images – a perfect example is a wedding shooter. They may need full-resolution images for some shots (such as family group portraits or formal shots of the bride and groom) that would potentially be printed in very large sizes. However, many candid shots taken at a typical wedding reception will rarely get enlarged beyond 8x10 inches (smaller than A4 size) and most prints will be even smaller.

Another example is a photographer called upon to photograph images for web use. In assignments like those, it may be preferable to shoot at smaller resolutions — still perfectly acceptable for online viewing, but much more manageable file sizes that are easier to store long-term. Unlike reduced-resolution JPEG images, Canon's small RAW files give almost the same control over image processing that you get with a traditional full-resolution RAW file. And, they are recorded at full 14-bit per channel bit depth, which is the same as full-resolution RAW files from EOS Digital SLRs.

"sRAW" options explained

Initially, EOS cameras like the EOS 50D designated reduced-resolution RAW image files by “sRAW 1” and “sRAW 2” (small-resolution RAW 1 being roughly equivalent to a Middle resolution JPEG and “sRAW 2” being similar in pixel dimensions to a Small JPEG file).

Canon has changed this on recent models to avoid confusion. The reduced-resolution RAW options are now more clearly labeled “mRAW” (Middle resolution RAW) and “sRAW” (Small resolution RAW). Here’s a look at the break down in terms of pixel resolution and approximate file size (in MB) for each image on the memory card, using the EOS 5D Mark III and EOS 7D as examples:

 

 

EOS 5D Mark III

EOS 7D

Effective sensor resolution 

22.1 MP

17.9 MP

RAW 

22.1 MP

17.9 MP

mRAW 

10.5 MP

10.0 MP

sRAW 

5.5 MP

4.5 MP

File size on card (in megabytes)

 

 

RAW 

27.1 MP

25.1 MP

mRAW 

19.1 MP

17.1 MP

sRAW 

15.1 MP

11.4 MP

CF Card capacity (images on 8GB card)

 

 

RAW 

260

300

mRAW 

370

420

sRAW 

480

675

Please note: figures above are approximate and will vary depending on subject matter, ISO and shooting conditions

 

You may notice that even though the resolution/pixel count follows a general ½ ~ ¼ pattern, compared to a full-resolution RAW file, that the file size does not. The reason is that these smaller sRAW files still retain a wealth of tonal information and detail (that’s largely why image quality from them remains amazing). While this does result in larger files than a reduced-resolution JPEG, they’re compact enough to significantly increase the number of shots you can fit onto a memory card. And, more importantly to some users, they’ll take up less space for long-term storage on external hard drives or wherever you permanently store your original RAW files.

Small RAW files for on-screen uses

When shooting for web use, remember that even the lowest-resolution sRAW settings on either camera will produce significantly higher resolution than most computer monitors currently deliver. For example, the sRAW setting in the EOS 7D generates a 2592x1728 pixel file, which slightly exceeds the pixel dimensions of Apple Computer’s™ 27-inch LED Cinema Display monitor. And the sRAW pixel resolution greatly exceeds the 1920x1080 pixel resolution of today’s Full HD display devices.

For typical on-screen use for websites, email or Microsoft PowerPoint presentations, these sRAW files provide more than enough resolution for image display.

mRAW is ideal for 4K-ready images

As 4K monitors, digital projectors and display devices begin to enter the marketplace, users may wonder how reduced-resolution RAW files in an EOS SLR match up to 4K resolution. Here’s a quick look:

  • 4K pixel resolution: 3840 x 2160 pixels (8.29 million total pixels; 16:9 aspect ratio)
  • EOS 5D Mark III “mRAW” resolution: 3960 x 2640 pixels (10.5 million total pixels)
  • EOS 7D “mRAW” resolution: 3888 x 2592 pixels (10.0 million total pixels)

In other words, the middle resolution RAW settings on most EOS cameras will produce a file with slightly greater horizontal pixel resolution than the official 3840x2160 count for 4K devices. mRAW settings may be ideal for users who need imagery for the web and 1080 “Full HD” devices today, but who want to be ready for the advent of 4K output devices in the future.

Obviously, shooting full-resolution RAW files and reducing their pixel count for on-screen use remains a viable option for many shooters while providing the peace of mind of knowing that if a large print is needed in the future, their files can handle it. For users who know that they’ll need to archive thousands of images for years, there will be cases where on-line or on-screen use is the only likely way their images will be used. And for these users, the reduced-resolution RAW options of recent Canon EOS SLRs is something that they may want to experiment with and get to know.

Prints from reduced-resolution RAW files

High resolution images are recommended for producing quality large prints. A conservative estimate of the largest prints a critical user could expect to get, with good levels detail and print quality, might be as follows:

 

 

EOS 5D Mark III

EOS 7D

RAW 

30"x40" or longer

20"x30" or longer

mRAW 

13"x19"

11"x14"

sRAW 

11"x14"

8.5"x11"

 

Please keep in mind that these are approximations. Some photographers may find they can print at sizes even larger than those indicated with quality that’s perfectly acceptable for their needs. Again, we strongly suggest that any EOS owner shoot some reduced-resolution RAW test images and create prints to check how the new small RAW feature will work for them. Understand the capabilities as they apply to your particular needs and you’ll be equipped to use the tools available in your camera to meet the needs at hand.

Added burst-rate performance with small RAW images

Since reduced-resolution RAW file sizes per image are smaller, it should come as no surprise that during high-speed continuous shooting, the “burst rate” (the number of continuous shots you can fire in a row without slowing down) increases.

An EOS 7D (equipped with firmware v. 2.0 or higher) can shoot up to 25 full-resolution RAW images in one uninterrupted, 8 fps (frames per second) burst. But if a shooter knew if their files would likely be strictly used for on-screen viewing, for example, switching to sRAW would roughly double the burst rate (48 continuous images; 53 if a fast UDMA-7 type CF card was used).

Two memory cards, two different RAW files of the same image

While all EOS cameras are capable of shooting RAW and JPEG image files (including the combination of a reduced-resolution RAW image and a full-resolution JPEG file on the same memory card), high-end EOS models that accept two memory cards, like the EOS 5D Mark III and EOS-1D X, add another capability: record one type of RAW file on one memory card and a different RAW file size on another memory card.

When card management is set to “Record Separately,” for occasions when two cards are installed in either the EOS 5D Mark III or EOS-1D X, users can freely set either card to record any of the possible file recording types offered by the camera. Thus, one card could record “mRAW” or “sRAW” images, while the other records full-resolution RAW image files.

Summary

Canon’s reduced-resolution RAW option directly addresses requests from different Canon SLR owners and provides them with an answer to an age-old problem: how to retain overall high image quality while reducing the overhead required to store the increasing number of files. There are certainly plenty of times when EOS owners will want to shoot RAW files using the camera’s full resolution. But when a reduced-resolution file will get the job done, the new small RAW options are a great tool to use instead and ultimately have the potential to save a lot of hard drive storage space over time.

The CDLC contributors are compensated spokespersons and actual users of the Canon products that they promote.

All images are copyright Bob Davis, Erika Silverstein

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