Troubleshooting Photos –
About Camera & Photo File Formats
When you took your new digital camera out of the box, it was almost certainly set to shoot in the JPEG format (.jpg), a universal format that is defined here and whose strengths and weaknesses are presented in considerable detail in About JPEG.
JPEG is the basic format for digital cameras, providing high quality reproduction, compact storage and fast processing as well as EXIF photo data (note how EXIF information is used for troubleshooting here, plus you never have to disfigure your photos with visible date stamps). Since digital cameras use JPEG as their primary format, their handling of the format is sure and speedy.
JPEG also gives instant gratification. People used to joke about the hundreds of rolls of film that were shot but never even looked at, because photo editing could be such a chore. JPEG on your computer is fast and fun, so digital photos get looked at, swapped and enjoyed.
JPEG is not, however, perfect for all purposes.
JPEG should never be used as an editing format because if they are opened, saved and closed too many times, JPEG images degrade to the point of developing visible artifacts. Accordingly, if there is a possibility that your work on a photo will extend over a period of time, you should save your working copy in the application's native format or a working format like TIFF (both are discussed below).
As a camera format, JPEG may not be ideal for people who want the last word in artistic control of their photos. When you take a JPEG, the camera quickly performs a series of operations that immediately make the picture an attractive representation of the scene. Those preparations, however, become a permanent part of the original image, so it's effectively impossible to undo them at a later date.
Alternatives for the camera and for editing follow.
RAW & DNG
RAW isn't a format, rather it's a class of file formats – RAW files capture the stream of image data right off the camera's sensor – it's unprocessed, raw data (hence the name) and the formats are individual to the camera manufacturer. Since no processing is done, you are free once you get back to your computer, to set whatever tone curve, sharpening, white balance or profile you want – it's the ultimate in artistic freedom.
RAW files are never directly edited; the RAW processor 'develops' the data and produces a new file in the desired format. Since the original file remains untouched and digital imaging keeps new and interesting options, people anticipate the possiblity of returning to their RAW files with new approaches, much as landscape photographer Ansel Adams returned repeatedly to the same negatives as his ideas and printing options changed. Moreover, since RAW is a 16-bit file (65536 levels per channel) rather than the 8 bits of JPEG (256 levels per channel), you can adjust the tone curve a bit more aggressively with minimal risk of loss of detail or banding.
Use of RAW was once limited to DSLR cameras , but is now included in many premium point-&-shoot cameras.
The camera saved this JPEG with the exposure balanced somewhere between the water and the bird overall, which meant that the white feathers were over-exposed and thus detail-less. Had the picture been shot as RAW, it would have been possible to retrieve some detail. The downside, however, would have been the need to buy more memory to accommodate the large RAW files and longer waits between shots in a camera that provided the RAW option, but wasn't really built for it.
RAW files come at a price:
- RAW files are big, typically about three to five times the size of your camera's maximum-size, maximum-quality JPEG, because unlike JPEG, they're not compressed, so 1) they fill up your memory card fast (less of an issue than it used to be, since memory is cheaper) and 2) they take longer for your camera to write to the memory card, so when the next good shot comes along, your camera may be busy (even with their top-of-the-line cameras, pro sports photographers almost always shoot JPEG for this reason);
- RAW files require computationally intensive processing to achieve their advantages (translation: you need a much more powerful computer, more RAM and more hard drive space than you need for fiddling with JPEGs);
- RAW files are a lot more work to prepare than JPEGs, because instead of the camera making a lot of decisions about the image, you have to sit at your computer and make those decisions, and wait while your computer applies them, which can take a fair bit of time; and finally,
- RAW files are proprietary and can only be read by specialized applications, unlike open formats like JPEG, so pro photographers and image librarians who think long-term are worried that RAW files might someday be un-openable if a major company went under. Although this seems far-fetched, consider that the original video tapes from the first moon landings cannot now be viewed until NASA finds the money to recreate the necessary tape machine.
The upshot is that RAW is not for everyone, and even for those for whom RAW is right, it's not the best choice all the time. Who wants to go through 400 holiday snapshots and individually white-balance them? ...and if you're just going to batch-process them, why not let the camera do it? Use RAW (if your camera offers it) in situations where you're not sure of issues like tone or white balance, when the light is really strange, etc. and want maximum freedom to make adjustments later. If you're interested in using RAW, check to see if your camera will record both a RAW and JPEG file of each shot. Often the JPEG will be in the camera's most compact size, but this gives you something to help you decide whether you want to expend a lot of effort on the shot (and it gives you something to e-mail to friends, if that's what you decide to use the shot for).
Adobe has attempted to address the issues of longevity and universality by promoting an open and universal format, DNG – a Digital Negative that:
- should be as accessible to future photographers as a 100-year-old film negative is to a contemporary darkroom; and
- that preserves all the RAW data;
- but that can be read by any editing or cataloguing application now and in the future.
It's a good idea, but at present, it seems to be treated as a solution in search of a problem.
TIFF
TIFF (Tagged Image File Format or .tif) is an old but flexible format that has been upgraded steadily since the 1980's (which makes it one of digital imaging's dinosaurs – but a dinosaur with legs). TIFF files are big, even when their built-in compression is on; a 1,000 x 1,000 pixel TIFF will be a 1 MB file, whereas a high-quality JPEG of similar size might be 200 kb (one-fifth the size) or less. On the plus side, they are:
- universal – as with JPEG, every computer image-editing and publishing program can handle them effortlessly;
- capable – since they can record a file at a bit depth of 8 or 16 bits per color channel, they are equally useful for day-to-day and fine-art-quality imaging; and
- lossless (compressed or not), so you can open a TIFF, work on it and save it all but endlessly without it suffering significant degradation – along with application files, they're a good choice as an editing file format while you're working on a photo.
The only limitations of TIFF are that it will not be able to save all the working steps of a complex editing process; usually you need to use your photo editor's own file format for that. Also TIFF cannot be used to display images on the Web.
Application or Program Files
Application or Program files are the application's proprietary file format. Examples are .psd for Photoshop and Photoshop Elements and .psp for Paint Shop Pro. They are not universal (although .psd can be read by many other programs) but they will save just about any operation that your image-editing application is capable of performing, so they're good working formats if you're doing something tricky.
GIF, PNG, Etc.
GIF is an old, all-but-obsolete format that should not be used for photos (because its limited color palette causes banding). It's good for Web icons and illustrations that have a limited palette because the files are small, they're understood even by the oldest browsers and they allow transparency, so a colored or patterned background will show through.
PNG is a recent format originally intended to end-run a legal threat to the continued use of GIF on the Web. As implemented, it became more than a free alternative to GIF, supporting a wider range of colors, better compression and smoother transitions between colors.
PNG is not normally thought of as a photo format – for comparable quality in a simple photo, it makes larger files than JPEG – but it is useful for making illustrations that combine text and photos or artwork because it excels at smooth color transitions while preserving the crisp edges that are essential for type. To achieve the same quality level in such a combination in JPEG requires a much larger file. PNG is used on this site when an accurate representation of a problem photo is needed; its fidelity means that a screen shot of a problem JPEG, for instance, is not further degraded by being re-saved.
Both of these images have transparent backgrounds surrounding the dice (which is not possible in JPEG), but the GIF on the left (12kb) has a much harder time handling the color transitions of the dice. Note the bands of color in the dice in the GIF, particularly in the green one, while the PNG (16kb) has the smooth transitions of a high-quality JPEG. GIF and PNG aren't normally used as photo formats (except for the situation described for the PNG above), but GIF's inability to handle color transitions demonstrates one important quality in a photo format. It's not uncommon to see a photo that has been accidentally saved as GIF and posted on the Web. The posterization (aka, banding) destroys any sense of reality.PDF and Other File Types
PDF (.pdf, Adobe Acrobat's file type) has the virtue of being readable by many applications, but is not necessarily editable by them and the files can be very large.
Other file types such as BMP, PICT, EPS, Pixar, Scitex and Targa are included as options in many applications to maintain backward compatibility with photos saved by older software. There is no reason to use them for new files.
