General Media Recommendations
Specifications and guidelines for digital media should come from specialists in the areas of Acquisition, Processing, and Archiving of digital media. "Archiving" includes the desire to keep the digital object into perpetuity.
The iDigBio DROID working groups have created workflows specific to image acquisition of museum specimens.
The Sustainability of Digital Formats Planning for Library of Congress Collections site is a good reference for images as well as other media types.
The following are examples of archival formats.
- Still Image
- TIFF (Tagged Image File Format)
- JP2 (JPEG 2000)
- DNG (Digital Negative)
- Moving Image
- MPEG-2 with AAC audio
- EPUB (Open eBook Publication Structure)
- PDF 1.4 (PDF/A)
Image recommendations are divided into four clusters: image acquisition, image archiving, image derivatives, and image distribution.
iDigBio offers the following recommendations for capturing, processing, archiving, and distributing digital images based on work of the Developing Robust Object-to-Image-to-Data Workflows Working Group (DROID), a review of industry standards, input from the broader collections community, and feedback from iDigBio staff.
Image Acquisition Recommendations
- Camera RAW is the preferred format for initial camera acquisition (this differs from the recommended Archiving format, see below)
- Scanner images should be recorded in 24 bit or higher at 300-600 ppi in TIFF format.
- Record at the highest native resolution available for the imaging device.
- Adjust white balance settings to match the light source.
- A visible color checker and scale are recommended, as appropriate.
- Color Spaces
- Adobe RGB or sRGB are the preferred color spaces and should be stated in the metadata.
- CMYK color space should be avoided (the intended output of CMYK is ink on paper, not a digital presentation).
- Image file names should be restricted to alpha numeric characters, without spaces or other special characters, underscore (_) and hyphen (–) excepted.
Image Archiving Recommendations
- Archiving images is strongly recommended and is viewed as a data provider's institutional responsibility, governed by institutional policy.
- Archived image files should be permanently retained in a secure, redundant environment on institutional infrastructure or commercial back-up services (not iDigBio)
- Uncompressed DNG or TIFF Uncompressed Bitmap TIFF at True Color (24 bit) or higher are the preferred archival formats.
- Images captured in proprietary camera RAW format (e.g., CR2, NEF, PEF, etc.) should be converted to Digital Negative format (DNG).
- Conversion to DNG can be accomplished via Adobe DNG Converter, available free from Adobe.com, or via Adobe Photoshop or Adobe Photoshop Lightroom.
Image Derivative Recommendations
- JPEG and JPEG 2000 images should be saved at their native dimensions (spatial resolution).
- Manually increasing resolution (e.g., alterations to image size or ppi or dpi settings) beyond that recorded by the camera may insert derived data or unwanted visual artifacts into an image file and is not recommended.
- EXIF, IPTC, and other image metadata (including JPEG 2000 XML data), including that added at time of processing, should be preserved in perpetuity and distributed with all derivative and distributed copies of images.
- Image processing should be carried out only on DNG or other RAW files to prevent accumulated data losses and potential image degradation by repeated processing of JPEG and TIFF image files.
- Excessive image manipulation or compositing, including sharpening, enhancing color saturation or balance, and adjusting contrast should be avoided.
Image Distribution Recommendations
- Images uploaded to aggregators and portals should be ‘fit for display’ on the web.
- JPEG format at camera's native resolution and with minimal compression is preferred.
- Lower quality images and lower resolution images should be distributed to aggregators and portals only when there is no higher quality image available.
Sounds, Documents, Models, and other types of Media
Recommendations and Standards should be drawn from the standards bodies or communities of practice surrounding a particular media type and from the Library of Congress.
Fit for Display
“Fit for Display” - This is a technical term that relates to file types and other inline text, encoding or attachments, that are not HTML and that are supported natively, or with helper applications, by web browsers. For instance, most browsers have native support for JPG and GIF images. This allows a browser to render the content of these files types for a user to view. All other types of web page content, like MP3, require a helper, either built-in or installed. In the preferences for a browser there are list of media types (or MIME types) paired with applications for ‘helping’ the browser display the content of that file reference. A helper application, sometimes called a plug-in, is software that knows how to render/display the content. Recall that HTML is the native language for web browsers. Other media types, like TIFF and DNG, that require an application other than the browser or plug-in to view their content, fall outside the definition of “Fit for Display”.
- Library of Congress - Sustainability of Digital Formats Planning for Library of Congress Collections
- Universal Photographic Digital Imaging Guidelines
- The AIC Guide to Digital Photography and Conservation Documentation American Institute for Conservation of Historic and Artistic Works
- Adobe Digital Negative (DNG) Specification
- DNG information from the American Society of Media Photogrophers' "Digital Photography Best Practices and Workflow".
- OpenRAW Project - Digital Image Preservation Through Open Documentation