Even illumination imaging (workflow)

The principles of this workflow are universally applicable to a wide range of setups, project scope and objects, regardless of their size, material, or complexity, and are considered best practice in professional imaging. It is a conceptual framework designed to guide cultural professionals through the essential stages of a project, from initial planning to final archival, to help making informed decisions about equipment, space, and logistics while ensuring that the final images meet the desired quality requirements.

Workflow

Workflows of the IWG Wiki are not step-by-step tutorials, but rather high-level, informative guides.
For more detailed help to adapt these workflows to your specific needs, please consult with your institutional imaging specialist or get in touch with IWG to find a professional.

Initial assessment and planning

Before any equipment is set up, a clear understanding of the project's goals, constraints, and requirements must be established. Guiding questions can help evaluating the requirements:

• What are the images used for? Why is this object being imaged? (e.g., condition report, publication, public access, research…).
• What are the desired outcomes? What specific information must be captured? What is the required level of detail?
• What is the required spatial resolution (pixels per unit)? How much of the object needs to be in focus?
• What are the physical constraints of the object and the environment? Consider size, handling and mounting requirements, location, available space, lighting of the environment.
• What equipment is available?
• Are there any logistical constraints? Consider any limits in time, number of images, file sizes.
• What are the archival requirements for the digital preservation of the files?

When multiple objects need to be photographed, a comprehensive list can help optimize the workflow. Objects can be grouped and ordered by scale and type of setup required. Prepare labels with the object's accession numbers, possibly including the treatment stage (before treatment (BT), during treatment (DT), after treatment (AT) and capture date. These can be included in the scene to help the reconciliation of the digital files with the physical object.

Setup

This phase involves the physical preparation of the imaging station. The design of the photographic setup depends on several factors, but mostly on the scale of the object (large vs. small), its geometry (three-dimensional vs. flat-like), and the optical properties of the materials (glossy vs. matte, translucent vs. blocked). Even illumination methods require the light to be evenly distributed throughout the scene, therefore designing the setup starting from the interaction light-object is a recommended approach. When a custom setup is prepared, it is common to start with an approximate positioning of the object, lights and camera, and then to adjust the geometry and the settings in an iterative way until the desired exposure and light evenness are met.

• Prepare the surface where to place the object. Depending on its scale and weight, it could be a sturdy table, a plinth or the floor.
• Select and install the background, if needed.
• Position the radiation sources and any light modifiers (reflectors, barn-doors, grids, softboxes, or umbrellas). If available, test for even and consistent exposure using an incident light meter.
• Position the camera.
• Secure the cables for safety to avoid tripping.
• Position the targets at the center of the scene.
• Set the power of the light sources and the camera settings.
• Set up the working station (i.e. a desk with the computer
• Capture an image of the target.
• Adjust the distance of the camera until the desired spatial resolution is achieved.
• Adjust the radiation intensity and/or the camera shutter speed until the correct exposure is met.
• Re-capture the targets for custom color profiling.
• Capture an image for flat-field correction.

Calibration and capture

The capture phase is preceded by the calibration of the setup to ensure standardized results throughout the imaging session. This generally includes the flat-field correction and the camera characterization, which is done with the creation of a custom color profile for the session. Additional evaluations could be done if the images need to comply with specific guidelines, like the Federal Agencies Digital Guidelines Initiative (FADGI) or the International Organization for Standards (ISO). In that case, measurable quality parameters are compared to the requirements, and the setup adjusted accordingly.

• Put the object in place; consider any required mounting.
• Place identification labels, if needed.
• Include targets in the scene, if possible.
• Shoot the required images of the object.
• Check the images for quality review (e.g. focus, composition, glare…). Adjust and re-capture if necessary.

Post-processing and export

This stage involves transforming the raw captured data into a final, usable image file. The operations are done using one or more applications designed to handle and edit RAW file formats, and often include options to streamline the editing process in batch.

While the degree of freedom to edit the files can vary between institutions, professionals, and intended use of the images, the focus is on faithful reproduction, consistency, and adherence to requirements established in the planning phase.

• Review and select the images.
• Apply the session color profile and flat-field correction.
• Fine-tune the global exposure and contrast without altering the visual integrity of the object, if allowed.
• Apply additional non-destructive edits (e.g., corrections for lens distortion and chromatic aberration).
• Embed key metadata (e.g., object ID or accession number, copyright, technical specifications…).
• Export the files in the required format and resolution for its intended use (e.g., TIFF for archive, JPEG for web).
• Apply the required naming convention.

Archival

The final step is to ensure the long-term preservation and accessibility of the images. Although this step occurs at the end of the workflow, some decisions may be taken at the initial planning stage. Guiding questions can help evaluating the requirements:

• Where will the files be stored? (e.g., local server, cloud storage, external hard drives).
• What are the long-term preservation requirements? (e.g., lossless formats like TIFF, RAW files, DNG).
• How will the files be backed up? Is there a system in place to prevent data loss?
• How will the metadata be managed? Is there a standard for embedding or associating metadata with the files?
• Who will have access to the files? What are the permissions and access controls?
• How will the raw files and edited versions be differentiated? Is there a clear naming or folder structure?