RGB digital cameras (RGB) compress the spectral information into a trichromatic system capable of approximately representing the actual colors of objects. Although RGB digital cameras follow the same compression philosophy as the human eye (OBS), the spectral sensitivity is different. To what extent they provide the same chromatic experiences is still an open question, especially with complex images. We addressed this question by comparing the actual colors derived from spectral imaging with those obtained with RGB cameras. The data from hyperspectral imaging of 50 natural scenes and 89 paintings was used to estimate the chromatic differences between OBS and RGB. The corresponding color errors were estimated and analyzed in the color spaces CIELAB (using the color difference formulas ΔE^*_ab and CIEDE2000), J_za_zb_z, and iCAM06. In CIELAB the most frequent error (using ΔE^*_ab) found was 5 for both paintings and natural scenes, a similarity that held for the other spaces tested. In addition, the distribution of errors across the color space shows that the errors are small in the achromatic region and increase with saturation. Overall, the results indicate that the chromatic errors estimated are close to the acceptance error and therefore RGB digital cameras are able to produce quite realistic colors of complex scenarios.

The ability to digitally remove the varnish layer during the pre-conservation diagnostic of a painting, without any chemical or physical intervention, could be an advantage because it enables the prediction of the outcome of the cleaning procedure of the protective layer and contributes to the treatment proposal. Two paintings from Adriano de Sousa Lopes were investigated by hyperspectral imaging in the visible range, before and after the varnish layer removal. The spectral reflectance was estimated in each case and its comparison used to assess the effect of the varnish layer removal. The simulated paintings with the old varnish layer were compared with those restored, with no varnish, by comparing the chromaticity coordinates and other chromatic descriptors. It was found that considering the effect of the varnish layer of each painting individually produces lower errors than considering the average of the varnish layer across paintings. It was also found that simulating the varnish layer removal without knowing the varnish transmittance produces limited results and that the errors are smaller if the chromatic content is assessed without considering lightness.

Laura Mora, Paolo Mora e Paul Philippot escreveram, por ocasião da primeira edição de Conservation des peintures murales, em 1975, que o tratteggio nunca tinha sido publicado em nenhuma revista técnica e que, apesar de ser praticado desde 1945, consideravam que ainda não tinha sido devidamente entendido, motivo pelo qual tentavam-no descrever detalhadamente. No inicio da segunda década do século XXI, várias são as situações, no caso concreto da reintegração cromática, em que persistem problemas de terminologia e alguma confusão acerca das técnicas de reintegração aplicadas em pintura, quer no discurso escrito, quer no discurso oral. Por esse motivo, o principal objectivo deste artigo é esclarecer a origem e os procedimentos originais de execução de algumas técnicas de reintegração cromática, as que normalmente se usam em pintura de cavalete em Portugal, tentando recorrer às fontes originais e a estudos específicos sobre o tema, bem como anotar particularidades na evolução das mesmas. O segundo propósito deste texto é facultar esta informação em língua portuguesa, algo inexistente até agora. Com base na interpretação das fontes bibliográficas concluiu-se que a mesma técnica pode ser praticada de modo diferente consoante a nacionalidade do conservador-restaurador, contribuindo para a evolução das técnicas existentes e para o aparecimento de outras.

Ana Bailão, Sandra Šustic, Retouching with mica pigments, e-conservation Journal 1, 2013, pp. 45-60