The effect of image size on the color appearance of image reproductions

Original and reproduced art are usually viewed under quite different viewing conditions. One of the interesting differences in viewing condition is size difference. The main focus of this research was investigation of the effect of image size on color perception of rendered images. This research had several goals. The first goal was to develop an experimental paradigm for measuring the effect of image size on color appearance. The second goal was to identify the most affected image attributes for changes of image size. The final goal was to design and evaluate algorithms to compensate for the change of visual angle (size). To achieve the first goal, an exploratory experiment was performed using a colorimetrically characterized digital projector and LCD. The projector and LCD were light emitting devices and in this sense were similar soft-copy media. The physical sizes of the reproduced images on the LCD and projector screen could be very different. Additionally, one could benefit from flexibility of soft-copy reproduction devices such as real-time image rendering, which is essential for adjustment experiments. The capability of the experimental paradigm in revealing the change of appearance for a change of visual angle (size) was demonstrated by conducting a paired-comparison experiment. Through contrast matching experiments, achromatic and chromatic contrast and mean luminance of an image were identified as the most affected attributes for changes of image size. Measurement of the extent and trend of changes for each attribute were measured using matching experiments. Proper algorithms to compensate for the image size effect were design and evaluated. The correction algorithms were tested versus traditional colorimetric image rendering using a paired-comparison technique. The paired-comparison results confirmed superiority of the algorithms over the traditional colorimetric image rendering for the size effect compensation

Efekt neonskoga proširivanja boje u procesu grafičke reprodukcije

Suvremeni sustavi vizualnih komunikacija na kojima se temelje i reprodukcijski procesi grafičke tehnologije permanentno se unaprijeđuju novim spoznajama vezanima uz rezultate istraživanja pojedinih vizualnih efekata. U okviru ovog doktorskog rada provedeno je istraživanje utjecaja različitih ciljanih parametara unutar procesa grafičke reprodukcije na intenzitet i pojavnost efekta neonskog proširivanja boje. Istraženo je djelovanje različitih medija (dvije tiskovne podloge i zaslon računala) u sklopu „cross-media“ reprodukcijskog sustava izrade grafičkih proizvoda, te uloga odabira boje umetnutog segmenta i pozadine primarnog stimulusa (različite kombinacije primarnih boja aditivne i suptraktivne sinteze) kao elementa dizajnerskih rješenja. Navedeni parametri procjenjivani su u različitim ambijentalnim uvjetima promatranja odnosno pod tri standardna CIE izvora svjetla. Efekt neonskog proširivanja boje manifestira se u pomaku pojavnosti boje stvaranjem prividnog proširenja boje primarnog stimulusa na pozadini grafičkih reprodukcija, u području rešetke veličine primarnog stimulusa, ali i u samom procesu oblikovanja predložaka u sklopu izrade dizajnerskih rješenja. Istraživanje efekta je provedeno na testnim uzorcima čiju osnovu predstavlja tzv. Ehrensteinov model - specifična geometrijska struktura koju čini ortogonalni sustav rešetkasto postavljenih linija oblikovanih preklapanjem različitih kombinacija boja primarnog stimulusa. Intenzitet efekta prikazan je izračunatim kolorimetrijskim razlikama boja E94 koje predstavljaju odstupanje manifestirane boje u efektu neonskog proširivanja boje u odnosu na boju medija reprodukcije. Pomak pojavnosti boje u efektu neonskog proširivanja boje opisan je kroz izračun promjene percepcijskih atributa boje - promjene svjetline L* , promjene kromatičnosti * ab C i promjene u tonu boje * ab H . Statistička analiza rezultata istraživanja provedena je primjenom odgovarajućih neparametarskih testova. Na osnovi dobivenih rezultata istraživanja dane su smjernice budućih istraživanja te uvjeti primjene istraživanih utjecajnih parametara vezani uz oblikovanje i otiskivanje grafičkih proizvoda u okolnostima potencijalne manifestacije efekta neonskog proširivanja

The Effect of Image Size on the Color Appearance of Image Reproductions

Archiving images of cultural heritage based on spectral imaging techniques is an active research area in imaging science. Original and reproduced art are usually viewed under quite different viewing conditions. One of the interesting differences in viewing condition is size difference. This leads to different surrounds and adaptation states. In order to investigate the effect of size in color perception of rendered images, a visual experiment was conducted using a colorimetrically characterized digital projector and LCD display. An image was rendered and projected on the screen. The same image was processed using various algorithms followed by rendering for the LCD display. These LCD rendered images, by definition, were considerably smaller than the projected image. Using a paired-comparison method, the effect of image size was investigated using a colorimetric image of Georges Seurat’s, “Sunday Afternoon on the Island of La Grande Jatte- 1884”. The Image rendered for LCD display with a linear increase in lightness resulted in a closer match to the image projected on screen than the original colorimetric rendered image and was perceived as a more accurate reproduction than the majority of algorithms tested