For the quality of scanned photos, both the choice of suitable file formats for images and the appropriate resolution are essential. Which image format offers the best quality, is supported by as many devices as possible and has only a small memory requirement?
The choice of right file formats for images depends also very much on the type of further processing of your file. In certain processes, applications or output devices, some formats do not work – or only to a limited extent under certain conditions.
The following paragraphs give you decision-making aids to determine the optimal one out of the different file formats for images:
- JPEG
- TIFF – Tagged Image File Format
- RAW
- DNG – Digital Negative Format
- PDF – Portable Dokument Format
- PSD – PhotoShop Document
- JPEG 2000
JPEG file format – compact but lossy
The term “JPEG” is an initialism/acronym for the Joint Photographic Experts Group, which created the standard in 1992. JPEG originally referred to a specific compression algorithm. Files of this type with the extension .jpg, .jpeg or – less often – .jpe are one application of this algorithm. The JPEG format can save up to 16.7 million colours per image. This is virtually the entire spectrum that can be perceived by the human eye.
The JPEG format works with lossy compression. It reduces the Raw data supplied by the digital camera or a scanner to a fraction of the original size. When you open a JPEG-file, the compression is reversed and the image unpacked into the working-memory (RAM) of the displaying device (PC, notebook, smartphone, tablet etc.).
The small size of the files has many advantages: more files fit on a data carrier and you can use them on the Internet without any problems. Also, JPEG is probably the most common standard. Virtually all viewing devices and photo editors support the format without any compatibility issues.
But it also has a serious disadvantage: You irreversibly loose image information by compression. The amount of the loss depends on the compression level you select. One can only achieve the minimum file size with high compression, resulting in a high loss of details.
JPEG is the most widely used of all file formats for images; it provides good, but lossy compression. If you don’t intend to further edit your files or if you need to save data-storage space, JPEG is probably the format to go for.
TIFF format – lossless image compression
TIFF (sometimes also TIF) works with almost all programs and under all operating systems as it is not a proprietary format. The ability to store image data in a lossless format makes a TIFF file a useful image archive. Unlike standard JPEG files, you can edit and resave a TIFF file using lossless compression (or none) without losing image quality.
You can choose between uncompressed or compressed TIFFs and you can also choose between LZW and the ZIP compression. Both methods work without loss, so the data compression does not deteriorate the picture quality.
You can use TIFF with almost all image editing and layout programs. If you intend to do further processing (or don’t know if you might in the future), the TIFF-format is the format of choice.
RAW-File formats for photos
A RAW format does not really exist. It is rather a generic term for the manufacturer-specific data formats of digital cameras. Almost every manufacturer created their own “secret raw-format”. There are now about 160 RAW formats. Known formats include CRW from Canon, NEF from Nikon, RAF from Fuji or PEF from Pentax. The term “raw” refers to the status of the data that is unprocessed.
A raw-file is thus a kind of digital negative. But before you can view it you need to process it. This is done already inside the camera or in an external raw converter, which is an own software (like Lightroom).
The software inside a camera processes the image with its own colour profile. It saturates the colour, compresses the image and then sharpens it. The result of this processing, which you can only influence very little, is then an image format file, like JPEG. Of course, you can also further process TIFF and JPEG images in a graphics program. Although, the basis is always an already changed or reduced amount of information.
Raw now offers the possibility of processing the raw data, i.e. the data recorded by the camera’s light-sensitive CCD chip, as they are. The is especially interesting for photographers and image editors with high demands who are prepared to invest a little manual work for a perfect picture.
Therefore, we always recommend taking photos in a raw-format (rather than jpg).
DNG – Digital Negative Format
Each camera manufacturer has different RAW-Files. Accordingly, there is a desire of many users to use a manufacturer-independent format, which enables you to use the file format even after a system change.
The intention of the digital negative (DNG) file format is to provide a uniform standard for camera raw files. Who knows if imaging programs will still open your camera’s own raw files in a few years. Adobe‘s freely accessible “digital negative” format records raw files from all manufacturers. Likewise, several cameras write DNG files directly.
Compared to standard camera raw files, DNG has some important advantages:
Compatibility for raw files
Software for DNG will probably be around longer than for the raw format of your particular camera model. You can therefore use the DNG file very well as an archiving format when you want to retain the raw data. The format ensures that the archived files are still accessible for several years.
Storage space
DNG files are effectively and losslessly compressed and have lower data-volume compared with other RAW formats, it has a lower data volume.
Clarity
DNG saves technical data of the camera (EXIF) as well as your IPTC texts directly in the DNG image file and not in separate »subsidiary documents« (XMP etc.).
PDF – Portable Dokument File
Adobe developed the PDF file format in the 1990s to present documents, including text formatting and images, in a manner independent of application software, hardware, and operating systems. It allows multi-page documents including watermarks, slide shows, annotations and password protection.
PDF files may contain a variety of content besides flat text and graphics. It can include logical structuring elements, interactive elements such as annotations and form-fields, layers, rich media (including video content), three-dimensional objects and various other data formats.
PSD – PhotoShop Document
The Photoshop file format PSD is used for montages, special cases and for versatile export to other programs of the Photoshop manufacturer Adobe, such as Illustrator, InDesign or GoLive;
It partially adopts Photoshop layers, effects, dissolving techniques and other specialities. Alternatives are: TIFF and PDF.
JPEG 2000
The JPEG process is not the only existing process for lossy compression of pictures. JPEG 2000 is a further development of the JPEG-format. It supposedly should achieve a better compression. However, is also has serious disadvantages, for example the computing capacity needed is higher and licence fees apply for the implementation into a software. So far on a broader level JPEG 2000 couldn’t establish itself and many graphic applications don’t support it.