Digitization of Paintings

Create high-quality digital copies of paintings with faithful color reproduction and high resolution, with no reflections nor geometric distortion

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► Nowadays, the technology of creating digital copies of paintings is of great importance, making it possible to archive paintings in the highest quality, that does not degrade with time. Digital copies have a very wide range of applications, meeting both the needs of the archive and the needs of promotion. Digital virtual galleries are becoming increasingly popular, allowing images to be viewed on any multimedia device, at any time, anywhere in the world. By having a device with very accurate colour reproduction, digital copies can be viewed in original quality without having to go to a museum or gallery. They also allow you to zoom in on parts of the image, allowing you to see individual pieces of the artwork in great detail.

Creating a digital version of the original image (digitization) is most often performed using a digital camera with a sufficiently large matrix. In any case, this process is not easy, it requires a lot of technical knowledge and experience. Key aspects of digitization include:

► Faithful color representation

For this purpose, in the digitization process, it is necessary to provide adequate illumination of the image, where it is crucial that it was done in the conditions of only light with one color temperature . If artificial light sources are used for lighting, then all of them must have the same color temperature. It is also excluded to make digital reproductions in conditions of mixing of the available light (natural or internal lighting) with the light used for digitization.

To ensure the ability to reproduce the natural white balance and colors of the image, it is necessary to use a color standard that will allow you to define / measure the correct parameters of white balance and colors under a given lighting. The professional and most popular color pattern is X-Rite ColorChecker, which enables the creation of a digital color definition (color profile) for given conditions, which, when used by professional graphics / photo processing software, allows for the most faithful representation of the image parameters.

► Lighting without reflections

For paintings created in painting techniques, for which a reflective surface reflecting light is characteristic (e.g. oil techniques, goldsmithing techniques), it is necessary to illuminate the image in such a way as to avoid unfavorable light reflections - this applies primarily to the content (surface) of the image, but it is this is also essential for the frame in which the painting is originally presented. The minimization of reflections during digitization cannot, however, reduce the details of the original image, which is its texture and possibly the texture of the material on which the image was painted.

In order to avoid reflections, it is necessary to skillfully arrange the lights and to disperse them through the use of appropriate light modifiers . In special cases, it may be necessary to use polarizing filters to minimize the effect of light reflected from the surface.

► Geometry of the photo

The image in the photo taken must be free from geometric distortions . One of these causes is the camera's optical system, which inherently introduces optical distortions. In order to eliminate them, the image should be photographed from the appropriate distance and the lens should ensure the natural geometry of the image. Most often they are long focal length lenses , less often medium focal lengths.

The second cause of geometric distortions may be improper positioning of the camera in relation to the photographed image - to avoid these distortions, the camera should be positioned in the image axis , i.e. the camera matrix should be parallel to the image plane, and the center of the lens should be aimed at the center of the image , perpendicular to its surface.

► The sharpness of the photo

To ensure the sharpness of the image, the picture should be taken with a large depth of field . The depth of field depends on the aperture value set in the camera, and on the parameters of the lens, the set focal length, the size of the camera's sensor and its distance from the photographed object. An experienced photographer knows all these aspects very well and can set the appropriate parameters to such values to achieve the highest sharpness.

The sharpness of the photo is also strongly influenced by the sensor sensitivity value setting at which the photo is taken. The higher the sensitivity, the stronger the drop in sharpness , so photos should be taken at the lowest sensitivity possible - preferably with the so-called camera native. This should take place regardless of the lighting intensity that we use during shooting - the correct exposure (exposure) is always adjusted with the exposure time.

To avoid blur which may result from camera shake, always take pictures with the camera mounted on a tripod and with the camera's remote / delayed release . It is also advisable to use the functions of the delayed shutter and turn off the image stabilization function (in the camera / in the lens).

Always focus on the central part of the image , which should evenly fill the camera matrix. You need to know the sharpness characteristics of the lens you are using and use the part of the field of view that provides the highest sharpness (in virtually all lenses sharpness decreases as you move away from the center of the field of view).

Likewise, the aperture value used should not be too large to avoid other undesirable optical effects. Each lens has its own characteristics that define the focal lengths at which the highest sharpness is ensured - the photographer performing the digitization must know this and use the recommended settings.

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► Noise in the photo, color tonality

To avoid digital noise in the recorded digital image, it is necessary to use the lowest possible sensitivity of the camera matrix . It is also very important that only the lowest sensitivity of the matrix will ensure the highest color tonality - the higher the sensitivity, the greater the color degradation.

► Photo manipulation

The exposure level of the photo should be such that in the subsequent digital processing it is not necessary to improve any exposure parameters. Virtually every modification of settings in post-production may have a negative impact on the image, introducing its destruction, even to a minimal extent. In post-production, you should also avoid additional sharpening of the photo and noise reduction - these issues should be addressed with the appropriate settings in the camera.

The key issues to be performed in the digital processing process are the removal of chromatic aberrations (resulting from the defects of the optical system of the lens) and the use of a prepared color profile of the image so as to fully reproduce the white balance and color values. An important issue is also to eliminate any possible vignetting . Each lens has a characteristic vignetting, however, it should be noted that additional vignetting may introduce the use of lens covers and winding filters on the lens, as well as the too small focal length of the lens. Therefore, it is important to check the current vignetting amount before taking the target image by recording a test photo taken with the use of a blank white surface - this will help to reduce vignetting to an appropriate extent during subsequent digital processing.

During image processing, any geometric distortions caused by natural defects of optical systems should also be removed.

► Other important issues

Before taking the target photo / series of photos, use a light meter to check the level of illumination of individual parts of the photographed image (center and in the four corners) and, based on the results, adjust the lighting so as to ensure the most even illumination of the entire image

If there is a risk of light from lighting falling into the lens, it is necessary to put a cover on the lens to avoid the effects of flare or fogging of the recorded photo. It should be remembered that each cover introduces an unfavorable vignetting effect - the greater the smaller the focal length of the lens. The use of the original cover - dedicated to a given lens model by the same manufacturer - will minimize vignetting. Please note that not all objects, including images, can be illuminated with any light. Especially historical paintings, of significant museum value, may require the use of certified lighting equipment , the light of which meets stringent standards (it does not harm the surface of the painting in the slightest extent). Therefore, you should always check with the client whether the images intended for digitization can be illuminated with our equipment.

Before the planned session, care should be taken to thoroughly clean the lens matrix - the higher the aperture value in the camera, the more clearly (sharper) all pollen and dirt are recorded, which may in special cases have a very negative impact on the recorded image. Their later removal from digital versions may be impossible or very difficult.

Photographs for digitization purposes should always be made in the raw RAW file format - this gives by far the greatest possibilities in the subsequent digital processing of the photo. Digital processing of photos should be carried out using 16-bit color space and in the widest possible color space, most often AdobeRGB . Only the finished photos should be converted to other spaces, formats and sizes.

It should also be borne in mind that the larger the sensor in the camera , the better the image quality is not only in terms of its resolution, but it also means less noise and greater color tonality .