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Guidelines for the production of digital imagery |
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These guidelines are a synthesis and outline summary of two major documents: the Universal Photographic Digital Imaging Guidelines www.updig.org and Pics4Press version 2 available at www.pass4press.com.
These documents contain detailed definitions of terms used here and a large amount of other detailed information which is not covered in these guidelines including a comprehensive glossary.
The GPA digital committee believes these guidelines provide a sound basis for any photographers’ digital workflow, but takes no responsibility for the professional decisions of individual photographers.
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1. ICC Colour Management
ICC profile-based colour management defines colour information in standard terms necessary for proper reproduction of images. Devices such as monitors, printers, and scanners should be profiled.
Photographers either generate their own profiles using one of the
many software packages available to do this, or they enlist the help
of one of the large number of consultancy firms who can create bespoke
profiles as a service. One highly regarded consultant who offers profiling
services is Neil Barstow – www.colourmanagement.net.
2. Monitor Calibration
Monitors should be calibrated and profiled with a hardware device, such as EyeOne (Gretag Macbeth). Visual calibration is not adequate for professional image editing. An accurate visual representation of the image is extremely important to the imaging process. Calibration standards range from:
- Gamma: 1.8 to 2.2
- White point: 5000K to 6500K
- Brightness levels: 80cd/m² to 140 cd/m²
As a general calibration guideline, use Gamma 2.2 and 6500K for both Windows and Mac. If you are preparing files for offset printing, you may find that most printers use Gamma 1.8 and 5000-5500K, particularly if they are using Mac computers. Brightness levels are set in relation to the room’s ambient lighting.
A calibrated and profiled monitor, in conjunction with good print profiles, will allow you to “soft-proof” the intended output. A daylight (5000K) light source at correct brightness is necessary to visually match monitor to print.
3. Colour Space
Colour space for RAW files (see below ‘File formats’) can be set in the camera or in post-production of the RAW file. Choosing a large-gamut space such as Adobe RGB (1998) is better for image editing, while shooting a narrow-gamut space such as sRGB is convenient if images do not require colour correction or editing, or if the images are intended for Web or sRGB lab prints. One consideration: A wide-gamut space can always be converted to a narrow space such as sRGB, but a narrow-gamut space converted to a wide space will not recapture the extra gamut.
Offset printing requires the CMYK colour space, a very different colour space from the RGB colour space produced by digital cameras. Converting from RGB to CMYK requires knowledge and skill, not just a simple mode conversion in Photoshop. CMYK conversions are best when done by someone with knowledge of the specific press and paper type. Photographers should supply RGB files.
4. File Formats
The best quality comes from shooting and editing in a RAW file format. The advantages of RAW file formats are: choosing colour space when the file is processed; greater bit depth; ability to adjust white balance, saturation, exposure (to a degree) and tonal characteristics; adjustable noise reduction; and correction for lens aberrations — all in a non-destructive way.
RAW files may be processed with a variety of software, from the camera maker’s own to many third party products, and even by using the built-in RAW processing of Apple and Windows operating systems.
Converting RAW files to DNG (Digital Negative) format is considered by many to be an excellent method for archiving RAW files. DNG is a more universal file format than camera-specific RAW formats like NEF or CR2. Camera formats are tied to each camera model and may not be supported by future software.
Editing of exposure, white balance, colour balance, contrast and saturation can all take place at the RAW processing stage. Many photographers find it convenient to add IPTC data at this stage also.
RAW files should normally converted to uncompressed TIFF format once editing has been carried out. If the TIFF file still contains 16 bit data then additional image editing can still be carried out. The TIFF file should be converted again for delivery to the client. For printing, uncompressed TIFF (8bit) is often preferred, although high-quality JPEGs (Level 10-12] can be visually indistinguishable from TIFFs and some printers prefer their smaller file size.
Photographers should never supply, or be asked to supply, RAW or DNG files to clients.
5. Naming Files
To avoid problems with files that will be transferred across computing platforms, name files with only the letters of the alphabet, numbers, hyphens and underscores. Do not use punctuation or symbols. Keep the full name (including extension) to 31 characters or less, including the 3-letter extension. Use file names that will not be duplicated. Multiple files with the same name cause problems for computers and people alike. Including the numeric date is an excellent method for creating unique names.
6. Resolution
Resolution of digital images is described either by pixel dimensions (width and height) for screen use or by physical size and resolution. Image resolution is expressed as pixels per inch (ppi), pixels per centimeter (ppc), or pixels per millimeter (ppm).
Inkjet prints normally need resolutions of 180 ppi to 360 pixels per inch (ppi) at the output size. Continuous-tone printing typically requires resolutions of 240 ppi to 400 ppi.
The offset-printing standard is often considered to be 300 ppi.
7. Sharpening
Some people like to use mild sharpening for creative purposes at the point of capture, but it should be done very carefully. Images should not be sharpened by the photographer in the image-editing process.
Process sharpening counters the loss of detail in the reproduction process. It is done after colour- and tone-correction, retouching, image sizing, etc. For these reasons this process is best done in post-production. The goal is an image that is acceptably sharp for viewing at its current size, but never over-sharpened.
Output sharpening is specific to the final output size and the output system (printing device, paper, ink, etc.) and is applied only as a final step before output.
More detailed guidelines on sharpening can be found at: www.computer-darkroom.com/sharpener/sharpener_page_1.htm
8. Metadata
The IPTC Core Schema is the current standard for embedding metadata in image files. Embedded metadata should include Creator and Copyright information as well as captions. Including useful and relevant information, including keywords, in metadata adds value to the image
9. File Delivery
Digital image files may be delivered on a variety of removable media, including hard drives, CD-Rs or DVD-Rs. Do not use adhesive labels on optical media, since they may separate and damage an optical drive. Printing directly on inkjet-writable CD-Rs or DVD-Rs is a good way to provide information such as your copyright, usage license, file lists and disclaimers. For speed and convenience, electronic delivery by FTP or e-mail may be used. All image files should have embedded metadata. (In the case of proprietary RAW files, the safest route is to have the metadata included in a sidecar file.) Image file delivery should include ReadMe files.
It is important to provide a ReadMe file in either PDF, HTML, or TXT format with all files that you deliver for output. Such files should specify image size(s), colour space(s), the copyright owner’s contact information, any licences granted and, if certain rights are being withheld, the words “other uses, reproduction or distribution are specifically prohibited.” The ReadMe file should also include disclaimers noting that recipients are responsible for following an ICC-based colour management workflow.
10. Guide Prints and Proofs
Guide prints and proofs can serve as a valuable reference point for digital files, but creating guide prints and proofs that accurately represent offset CMYK printing requires knowledge of printer profiles and colour management. For this reason this should be avoided in most cases.
11. Digital Image Workflow
No single workflow suits all photographers or all clients. A good digital workflow is the most efficient and automated way to get the job done. It should satisfy the clients’ needs, embed necessary information [metadata], embed colour profiles, and automate the archiving and backup of files. A good workflow saves time and protects against both loss of images and loss of work done to the images. There are many software options to choose from when you are constructing a digital workflow. New programmes that aim to be all-in-one solutions are constantly being introduced. You will need to test to see which programmes, or combination of programmes, give you the right combination of efficiency, speed, and quality.
In many cases the following guidelines will apply:
- Keep it simple.
- One piece of software – Photoshop CS2 - will provide all of the functions needed to create a simple and efficient workflow. This includes conversion of RAW files (ACR), cataloguing and Metadata input (Bridge) and the production of ‘contact sheets’ and web pages.
- Learn how to create and use Photoshop Actions – this will greatly speed up the workflow
- Treat each image as a unique piece of art – do not automate the process at the expense of artistic judgement.
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Checklist |
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Issue
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Typical Setting |
Notes |
Dimensions
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According to Output size |
300 dpi is typical for magazines |
| Format |
Tiff (8bits/channel). Jpeg
may
also be acceptable
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No RAW files. Files should not contain 16-bit information, layers, extra channels or annotations. |
Compression
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None |
Jpegs must use highest quality setting (12) |
Colour space
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Adobe RGB (1998) |
sRGB IEC61966-2.1 for web use |
| Sharpening |
None |
Sharpening should only be applied when final output size is known (ie not in file supplied to client)
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| Colour balance |
Files should be colour
balanced
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| Colour correction |
Free of unwanted colour
casts
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| File extensions |
i.e - .tif, .jpg. Always add
file extensions (Mac)
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Essential for cross-platform compatibility |
| Captioning |
IPTC |
Caption, credit, copyright essential. Keywords where appropriate
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