must minimize light scattering as much as possible, transparency is necessary. Microfacet model: According to Snell's laws, light flux arriving on a perfectly smooth surface is reflected in a single direction, called the specular reflection. Using Fresnel's laws, reflectance is determined by angle of incidence on the surface, refractive index, and polarized light state. When the surface is rough, light scatters in multiple directions with its intensity varying according to the angle of incidence, direction of reflection, and roughness profile. Torrance and Sparrow proposed a model that assumes a set of the mirror-like microfacets on a rough surface that can be used to predict reflectance. The Cook-Torrance model is based on the Torrance - Sparrow model and is utilized as a computer graphics technique that expresses a genuine glossy-like impression. When roughness is isotropic, the Cook-Torrance model predicts reflectance by assuming the existence of randomly facing rough surfaces that are then represented by a set of mirror-like microfacets. This model presents the scattering phenomenon using the bidirectional reflectance distribution function (BRDF), which sets forth the reflectance of a target as a function of illumination geometry and viewing geometry. The BRDF depends on wavelength, and is determined by the structural and optical properties of the surface. In this case, the BRDF of a surface is calculated according to the following parameters: incident angle, observation angle, surface roughness, and refractive index. The BRDF is the result of a combination of three factors: reflectance or transmittance factor F, the microfacet orientation distribution function D, and the geometrical attenuation factor G. In this study, the slope distribution obtained by the surface roughness measurement of an inkjet paper sample is used in place of orientation distribution function D.6 Optical properties of the ink absorbing layer: Coating colors, which consist of pigments and binders, are applied onto a base sheet. After it dried, the coating forms the ink absorbing layer. The porous structure of the layer is formed during the coating and drying process. Consequently, the coating composition and the production process affect the refractive index of the surface layer. Incident light applied to the ink absorbing layer is reflected, and refracted, in accordance with Fresnel's law. Portions of the light refracted in the ink absorbing layer can be reflected from the surface of the base sheet and ejected from the ink absorbing layer as outgoing light. In order to estimate reflected light intensity distribution from the factors mentioned above, it is necessary to consider the refractive indices and smoothness of the ink absorbing layer and base paper. The surface profile as the distribution function, and the refractive index of ink absorbing layer, are measured respectively. Experiment Paper samples: All the paper samples used were for inkjet printer and included a photo quality type, a high gloss type, a medium grade type and a silky surface finishing type. Table 1 lists the paper samples used. The coating structures of inkjet paper types range from a simple single-layer coating to more complex multilayered structures. Table 1: Paper samples Paper Grade Basis weight [g/㎡ ] Brightness [％ ] A Photo gloss 245 90 B Photo gloss 300 96 C High gloss 190 101 D Silky finishing 250 92 Surface profile measurement: The topography of the surface of the papers was measured with a mechanical surface profilometer SE-30D, Kosaka Lab.. A diamond stylus with a radius of 2 µm and a load of 0.7 mN was scanned in the longitudinal direction. Optical measurement and prediction of reflection: A goniophotometer (Optec co., GP-1) was used to obtain the angular distribution of reflected light from the inkjet papers. The geometry for the measurement deals only with zenithal angle of the light source and observation direction. The azimuthal angle is fixed at 180°. The angular distribution of reflected light from the inkjet paper samples was measured at each 10° of incident angle. Parallel light from a halogen lamp was radiated onto the sample, and the reflected light was detected through the lens of a photomultiplier receptor. The signal from the photomultiplier receptor was then imported into a personal computer as digital data. Reflectance distribution is calculated on the basis of microfacet model. During this process, the measured surface profile is converted into height data. Interpolation between the height data obtained by the quadratic function provides the slope of surface. The above-mentioned slope angle is utilized as the microfacet distribution function. By regarding the pores or cracks of the surface as V grooves, the optical attenuation caused by the surface geometry can then be considered. Based on these factors, reflectance distribution can be estimated using Monte Carlo method. Results and discussion Surface profile of inkjet papers: The results of the measurements conducted on the four types of inkjet paper are shown in Figure 2. It was determined that the use of a relatively large stylus (○ µm) and light loading (○ mN) could minimize surface damage. High gloss inkjet paper appears to be manufactured using cast coating methods for based paper and by the multilayer coating method for RC-based paper. It was found that cast coating methods tend to incur defects (such as cracks) on their surfaces.7 However, when an RC-based paper is used, undulation is generated by substrate waviness. As substrate undulation deteriorates gloss quality, improvements are under investigation.8 Ruggedness, surface undulation, and minute grooves are shown in Figure 2. These are presumed to be caused by the above-mentioned factors and affect the reflected light intensity distribution of the specular direction.
Paper choice is important if you want high-quality, long-lasting prints. The paper must be compatible with your printer and have the right look and feel for the image printed on it. Its surface should also be able to accept the ink without letting it spread. To achieve these objectives, all inkjet papers have coated surfaces that impart certain qualities with respect to flatness, surface texture and ink absorbency.
Porous papers  Porous papers are more resistant to moisture and humidity than swellable papers. However, without a protective polymer layer, the ink droplets are vulnerable to atmospheric pollutants. They are also more susceptible to physical damage when handled. Porous paper is the preferred paper to use with pigment-based inks, which are less affected by atmospheric contaminants than dye-based inks. Pigment-based inks also have much better lightfastness characteristics and ozone resistance on porous papers than dye-based inks.
Cotton rag papers
Other Media Most canvas media is fairly thick; typically between 350 and 450 grams/square metre (gsm) so, if you wish to make canvas prints at home, your printer must be able to handle media of this thickness. Very few desktop printers can – and those that are capable of printing on canvas are mostly professional models.
Canvas is usually sold in rolls, which are designed for large format printers. However, cut sheet packs of canvas are distributed by the following companies: If you’d like to explore printing on canvas, Hahnemuhle’s Gallerie Wrap system provides an easy way to mount canvas prints and requires no special tools. Each kit contains one or two sheets of canvas media plus adhesive-coated stretcher bars and full instructions for printing and mounting the image for display. A step-by-step demonstration can be viewed at www.hahnemuhledirect.com. Click on the Gallerie Wrap link. Hahnemuhle’s Gallerie Wrap system provides an easy way to mount canvas prints. For environmentally-conscious photographers who would like to use non-timber-based media, Hahnemuhle produces fine art papers from bamboo and sugar cane by-products. Both are certified as archival grade and acid free. Hahnemuhle’s new Bamboo and Sugar Cane papers are designed to appeal to environmentally-conscious photographers. Booksmart has recently introduced a range of inkjet printable fine art metal media with a coating that accepts most popular inkjet printer inks. The metal sheets have an adhesive backing to make mounting easier. Five surfaces are available: Matte Silver, Satin Silver, Satin White, Satin Gold and Brushed Silver. Booksmart’s Fine Art Metals media give photographers the opportunity to print on metallic surfaces which impart a radically different look and feel to images. The media range in thickness from 0.127mm thick to 0.3mm thick, depending on sheet size. A4 and A3 sheets are available in both thicknesses. Larger sheets (up to 508 x 1372 mm) are mainly 0.3mm thick. Full details of this range can be found at www.kayell.com.au. Do-it-yourself photographers who would like to create their own media can take advantage of the Ink-Aid products from Image Products (www.imageproductsonline.com.au). These specially-formulated coating materials can be applied to substrates like paper, plastic, metal, glass and vinyl. (Make sure your printer is able to handle these media.) Several surfaces are available, including white matte, clear gloss and iridescent gold. A sample pack containing six 125 ml bottles of each coating (enough to coat three A4 sheets) is available for $46.14. The Ink Aid sample kit provides enough coating material to cover three sheets of A4 paper for each of six different coatings.
Sample Packs Image Science stocks A4 Sample Packs for Harman, Museo, Ilford Galerie, Canson Infinity and Hahnemuhle. Details from www.imagescience.com.au. Giclee Media Supplies offers several A4 sample packs covering the Eterna Fine Art Paper, GMS Photographic paper and Moab fine art papers for RRPs from $15 to $22.50. Single-sheet samples of Breathing Color Brilliance 1 and Breathing Color Brilliance 2 canvas are also available in A3+ size. For details, visit http://gicleemedia.com.au/gms/home.php. Other distributors may also offer sample packs but details were not provided on their websites. Sample packs allow you to try out a range of different surfaces and weights without having to invest in a full pack of one particular paper.
Weight and Thickness Photo printing papers should be at least 170 gsm in weight; preferably 190-250 gsm, although some glossy papers are available with 300gsm weight. Paper thickness is usually expressed in millimetres. The table below provides some equivalents for popular photo papers.
Unfortunately, most home printers are unable to use heavy papers as their paper feed mechanisms are not robust enough to handle the weight and stiffness of thicker media. Some printers can accept heavier papers through a special chute or slot and most will only accept one sheet of heavy paper at a time. Check your printer’s specifications to find the maximum paper weight it can handle. Be cautious when buying lighter-weight papers, especially if they are very cheap. Thin, lightweight papers may not be totally opaque. This factor is particularly important when selecting double-sided paper for printing photo books, as you need to be sure the image printed on the reverse side of the sheet does not show through and affect the picture on the front. Opaque papers are also better for prints that will be framed or put into albums because they prevent backing colours from influencing the appearance of the print.
Fine Art Printing Papers Among the specialist paper manufacturers, the leading brands of fine art inkjet printing media are Canson, Hahnemuhle, Arches, Somerset, Innova, Ilford, Harman, Museo, Chromajet, Lumijet, Lyson and Moab. Suppliers of these papers include:
DES Pty Ltd (www.des-pl.com.au) Always look for media with ICC profiles and buy from suppliers that offer these profiles as free downloads from their websites. Having an ICC profile for a particular paper makes it easier to ensure that what you see on your computer screen will be a good match for the printed output. This can be a significant time- and cost-saver when you are printing your digital images. If you want your prints to retain their colours for the longest possible time, look for Fine Art papers with no optical brighteners, such as these heavyweight papers from Canson. |
What are the two main characteristics of inkjet printer paper that affect the image the most?
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