Understanding file types for digital photography
Digital images are saved as files after the sensor has captured the scene you want to photograph. The camera saves the files on a memory card and normally you will later transfer them to the computer where you can print them, send them to a friend or client via email or show them on the web. Or you can decide to first adjust the images in the computer and later do one of those things.
Most cameras either capture RAW or JPEG files. Later, on the computer, you can save the files in other formats like TIFF or PSD. Let's have a look at the available file formats and their characteristics, advantages and disadvantages. Only when you know what the difference between the various format is, can you make an informed decision about which format to use.
This is what most people, who want the highest quality, use.
RAW is not an official format like JPEG which is an open standard. Instead most camera manufactures use their own and proprietary format for their RAW files. That is, the RAW file that comes out of a Nikon D3 is different from one which comes out from a Canon EOS 5D Mark II.
RAW files are sometimes called a "digital negative" because it contains the data as captured by the sensor without any processing by the camera applied.
RAW images store settings like white-balance, sharpness or saturation separate from the actual image data. This is a huge difference to other formats like JPEG where the camera applies those settings in camera when producing the JPEG file.
The huge advantage of this is, that you can later adjust all those values yourself using a RAW converter. Every camera manufacturer ships a software that can convert their RAW files. But other companies also offer RAW converters that can work with those files. The most popular is Adobe Camera RAW which comes with Photoshop and is also part of Lightroom.
RAW files store much more information than JPEG files. JPEGs are restricted to 8 bit for each color channel (Red, Green, Blue). This is quite a lot and allows for more than 16 Million colors, more than the human eye can distinguish. But when you edit a JPEG heavily using software like Photoshop, you lose more and more information and after a while and many savings of the file you see the quality degrade heavily.
RAW files store 12 or 14 bit (depending on the camera model) which gives you a lot more freedom when editing those images. A RAW file gives you all the data that you camera uses to produce a JPEG file. But with modern software like Lightroom, you have a lot more options for getting the most out of a RAW file than your camera has.
When you photograph subjects for which the exposure is difficult like a scene with a high dynamic range, RAW files allow for better adjustments and also better recovery of blown out highlights. Of course, if a part of an image is totally blown out (that is all three color channels ore clipped), no RAW converter can restore any image date, but as long as at least some information is available, it is amazing what modern RAW converters can do. No way to do this with a JPEG file.
Nothing's perfect of course, so RAW files also have some disadvantages.
First, to really get the most out of a RAW file, post processing using a RAW converter is a must. Modern RAW converters like Adobe Camera RAW (also used in Lightroom) are quite easy to use and very powerful but still there is some time involved for each image you want to print or make available on the web.
Another disadvantage is that you need a special software (the RAW converter) to view them. Files like JPEG can be viewed by many more programs including all web browsers.
Another disadvantage of RAW files is their larger size compared to JPEG files. This means, you need more storage space in terms of hard disks or DVDs.
RAW files also fill up the buffer in your camera faster. If you shoot a lot of action like sports or birds in flight, the buffer of your camera will fill up faster and more often and you have to wait a short amount of time until you can shoot again. This can mean a lost shot. On the other side, modern professional cameras (for example, a Nikon D3) are so fast that this is less and less of an issue.
For me those disadvantages are not really important and I recommend using RAW whenever you want the best quality. I shoot only RAW, except when I just want to make some quick snapshots of a family event or something else where the quality of a JPEG is enough. But for all my serious nature photography I only shoot RAW.
The fact that RAW files need more space on the hard disk is not really a problem for me. Modern hard disk today are huge - you can already buy internal and external disks with more than 1 TeraByte for a very low price. So storage space is not really a problem.
DNG is a invention by Adobe. It is an open RAW format which Adobe hopes to establish as a standard RAW format. That advantage is that you would no longer work with proprietary formats like those from Canon or Nikon which makes you less dependent on those formats. Some people fear that they won't be able to read proprietary RAW formats in a few years and DNG is the solution as it is an open format. Its specification is available on the Internet (See here for more: http://www.adobe.com/products/dng.
Right now some camera manufactures support DNG but as long as the two big ones (Nikon and Canon) use their own format, it will never become a true standard. Adobe provides a tool that allows you to convert your proprietary RAW formats to DNG. If you use Lightroom, you can convert them to DNG when importing them into your Lightroom catalog.
I don't think that Nikon or Canon shooters won't be able to read their files in the future. Even if one of those companies will go bankrupt in the future there will always be some tool to read them (including Adobe products like Lightroom of Photoshop). And some company or programmer will provide tools to convert them into something like DNG.
At the moment using DNG is a matter of taste. I don't use it right now but may do so in the future.
JPEG is the most common format to show images on the web. If you show your pictures in a photo forum, you will normally use JPEG files (most forums don't even allow other formats).
One great advantage of JPEGs is, that all web browsers like Firefox, Safari, Google Chrome or Internet Explorer can display them without the need to install additional plugins.
JPEG uses a lossy compression algorithm, which means when you save a JPEG file, image data is lost. This helps to save data and reduce the file size. This is great for storing huge amounts of files and for showing them on the web of sending them via email. JPEG allows for a pretty strong compression without much loss of quality. Still, if you want to preserve the highest quality possible, make sure you choose the highest possible quality when saving.
When saving JPEGs in programs like Photoshop you can choose different quality settings. A high quality setting will compress the data only slightly and produces high quality and large files. A low quality setting will produce much smaller files but the image quality will suffer.
Only save an image as JPEG after you've done all the editing. If you save a JPEG file, open and save it again, you will lose some quality. Every time you save a JPEG file, you reduce its quality.
JPEGs use only 8 bit for every color channel instead of RAW files which use 12 or 14 bit with most cameras. This reduces the flexibility when editing your images (see above in the RAW section for more information).
A big advantage of JPEG is speed. You can apply many settings like white-balance, sharpness or saturation in camera and if you've done everything right (like correct exposure), you can get a high quality file out of the camera. Sport photographers who need their images published often minutes after they took them, often use the JPEG format.
Many other photographers like portrait or nature photographers normally use RAW files as they give them more flexibility and allow a higher quality if processed correctly.
For all my nature photography, I shoot only RAW.
TIFF stands for Tagged Image File Format. Now, only few cameras offer the option to save TIFF images instead of JPEG or RAW. And when they do, often only 8 bit TIFFs are stored in order to save space on the flash card. TIFF files are larger than JPEG files but don't offer all the advantages of RAW files so there is no point in using them when taking the picture. But TIFFs are very popular as a format for saving after you have edited a file in Photoshop. TIFF, contrary to JPEG, supports 16 bit for each color channel, allowing a higher quality and more room for future edition. So, when saving TIFF files from inside Photoshop, make sure you save them as 16 bit files.
PSD stands for Photoshop Document Format. It's used by Adobe Photoshop to store image data. It supports 16 bit for each color channel and can also save layers. It is not as widely used among non Adobe software as the TIFF format. If you process your files in Photoshop and make heavy use of layers, PSD is an option, especially if you use only Photoshop or other Adobe programs to read them.
The above mentioned formats are all that you need for serious work. When presenting files on the web, GIF and PNG are popular. GIFs are not really suitable for photos as they allow only 256 colors which would ruin your pictures. GIFs are normally used to display graphics like buttons.
PNG was invented to replace GIF as there were patent issues with GIF. For photographs, JPEG is preferred over PNG on the web as PNG uses a lossless compression which would make the files bigger than JPEGs which uses a compression algorithms designed for photographic data.
If you want to best quality and total control in the digital darkroom, shoot RAW. Some cameras allow to shoot both RAW and JPEG at the same time. This may be a good idea if you want the advantages of the RAW format but also want something to use right out of the camera. I don't shoot both formats as I can always generate a JPEG from the RAW file and normally I don't need my pictures right away.
I try to do as much as possible in Lightroom and only "develop" my RAW files there. When I need them for the web I export them as JPEG. For many pictures, this means I never have to touch Photoshop and there is no need to save an image in TIFF or PSD. Lightroom does not alter the RAW file but stores everything as metadata in its database so the original RAW files are not altered and I can always get back to the original.
When I do use Photoshop, because I want to do something to an image Lightroom cannot do (for example when I need layers), I save the result as a 16bit TIFF file.
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