|Image Sushi: Raw vs. Cooked Images or
how to decide which digital image format is right for you
by Jim McGee
In his series on digital work flow Moose Peterson advocated using JPEG fine mode for shooting rather than higher resolution TIFF modes or the highest resolution raw file modes that are available with most serious consumer digital and on all pro digital cameras. His theory was that if you do everything right, as you would have to do when shooting film, and nail the image, JPEG will give adequate quality for publishable images. Moose has an impressive record of having exactly these kinds of images published.
In a perfect world where we all get the chance to shoot as much as Moose I would agree whole-heartedly. But there are times when photographers may want to consider shooting in Raw mode.
First you should understand the pros and cons of each mode. JPEG has been widely criticized for the fact that every time you save a JPEG image some image data is lost due to compression. There is a cumulative effect since this occurs every time you save the image. Over time the effects become noticeable as artifacts in the image. Artifacts are things that were not in the original image. They can manifest themselves as apparent color shifts due to compression, banding, boxy areas, and loss of sharpness. None of which is good.
But the amount of image degradation has been greatly overstated in the press, and particularly in some online news groups. These folks would have you believe a hi-res JPEG image you sharpen and save before printing will be somehow flawed. This is pure bull. It takes repeated saving of the data before any kind of degradation becomes obvious. How many times you can save an image before artifacts become visible depends on a number of variables such as file size, amount of compression used, and the nature of the image itself such as how much continuous tone area the image contains (sky for example). As a general rule of thumb low res JPEGs will show degradation much more quickly than hi res JPEGs.
In other words if you know that with your particular digital camera you're going to bring every image in, sharpen it, and tweak the saturation before saving you have nothing to worry about. If you think you may reopen and save it many times as you work with the image, then degradation is an issue. Also if you're doing a lot of digital dodging and burning to an image to create a fine art print and saving after each operation, then degradation may be an issue.
There are a couple of simple ways to deal with the whole issue of JPEG image degradation. You can save all of your original files to one directory as JPEGs and only work on copies. Another solution is to re-save the images created as JPEGs in your camera as TIFF files on your hard disk and then work on them as TIFFs saving as often as you like. There is no image degradation when saving a TIFF file.
If your camera supports it, you can also capture images directly into TIFF mode. As stated above, TIFF files can be saved as much as you want with no degradation. The price you pay is that TIFF files are significantly larger than JPEG files; that means they'll take up a lot more space on your memory card, they'll take longer to upload into your computer, and they'll take up more room on your hard drive once you get them there.
Sometimes You Want to Go Raw
So what is a raw file? Well the details will vary from camera to camera but the basics don't. A digital camera captures an image when the shutter is tripped and the CCD is exposed to light. The camera takes that raw image data and applies a set of filters to the image, just as you would in PhotoShop, based upon your camera settings. The difference is that those filters are optimized to the way your CCD records light - while PhotoShop's are not.
Those image filters typically include things like sharpness, tone, color saturation, and white balance correction. If your camera is set to JPEG mode the final image, after all the corrections, is what is saved to disk. Capture the image in raw mode and the original CCD data along with your camera settings are all captured to the file.
Its important to understand that a print of the raw file without any changes will look identical to a high resolution JPEG file captured at the same time. That is because you'll need special software to read the raw file. That software is usually bundled with the camera as a PhotoShop plug-in. The plug-in applies all the settings captured in the raw file to the raw image data before the file is opened up in PhotoShop - just as the software in the camera would have done. So the file opened in PhotoShop is virtually identical to the file that would have bee saved by the camera.
The advantage to raw mode is that you can use software to change the filters that are applied to the raw mode file. This is the equivalent of being able to change your mind about your camera settings after your capture the image. Even one, two, or five years later!
Now imagine this scenario. You go out and do a model shoot. On your laptop screen everything looks OK. You shoot the equivalent of 15 rolls of film or 540 images. A day later you're looking at the images on your workstation and you notice the white balance is off a bit on all the images. This is the equivalent of using the wrong film type and/or filters for the available light.
If you shot in JPEG you'd have a choice of editing 540 images in PhotoShop or redoing the entire shoot. Both are expensive and ugly options.
But if you did the shoot in raw mode you have the option of changing the white balance after the image is captured. Depending on the software for your camera, you might even be able to do this globally for an entire directory in a single operation! That is powerful. More importantly it could save your butt.
A Learning Tool
Let's say you shoot mostly landscapes. It's near sunset and the light is tricky. You set up on a tripod and bracket at 2/3rds of a stop above and below the meter reading in raw mode.
Now back at your desk load the images in and choose the one you feel is the best starting point. Most photographers use different films in different situations to control saturation and mood in their photos. Experiment with tone and saturation of your image to get a combination of settings that imitate a favorite film or films. Record those settings so you can choose what kind of "film" you want to use in the field - just as you would with a film camera.
Next, experiment with the white balance. White balance is probably the most misunderstood setting in digital photography and the accuracy of white balance settings varies greatly from camera to camera and under differing conditions.
Is auto white balance the best answer with your rig - or do your images look better with some white balance compensation dialed in? How about sharpness? Are you better off doing some sharpening in-camera, or doing it all in PhotoShop? If there's no difference let the camera do it to save you a step later. But beware! The amount of sharpening you want to do may change with the subject you're shooting.
The Bottom Line