Wallpaper Color Space Fundamentals

11/01/2008 by conrad.

Computer monitor screens emit color in RGB colour space (red, green, blue) light. Although all colors of the visible colour spectrum can be produced by mixing red, green and blue, computer monitors are capable of showing only a limited colour gamut. Colour gamut is the visible spectrum.

Where monitors emit light, printed paper absorbs or reflects specific wavelengths of light. Cyan, magenta, yellow inks act as filters, subtracting varying degrees of red, green and blue from white light to produce a selective gamut of spectral colour. Like monitors, printing inks also produce a color gamut that is only a subset of the visible spectrum, although the range is not the same for both. Consequently, the same art displayed on a computer monitor may not match to that printed in a publication. Also, because printing processes such as offset lithography use CMYK (cyan, magenta, yellow, black) inks, digital art must be converted to CMYK color for print. Many printers now prefer digital art files be supplied in the RGB color space with ICC profiles attached. Images can then be converted to the CMYK color space by the printer using color management methods that honor profiles if present; this helps preserve the best possible detail and vibrancy.

Refer to the Instructions for Authors for your journal to determine if files should be supplied as RGB or CMYK. Some printers may prefer your files be delivered in RGB with ICC profiles attached, as this allows the printer to use color management methods when converting to CMYK. Other printers may prefer your files in the CMYK (Cyan/Magenta/Yellow/Black) mode, as this is the mode required for the printing process. If an RGB (Red/Green/Blue) file is submitted, it must be converted to CMYK for print. When the conversion takes place, color shifts can occur and TSG will do our best to reproduce as close of a match to your printed output as possible.

It can sometimes be difficult to visualize the reason for color shift in color space conversion. The best way to see the color differences between the CMYK and RGB color spaces is to look at a color gamut comparison chart. The chart to the left plots the visible color spectrum as the large “horse shoe” area, and within this is a plot of the CMYK colors, and the RGB colors. You can see that in some areas the RGB color space is “outside” that of the CMYK space. It is these colors that will be affected by a conversion from RGB to CMYK

Most desktop scanners, digital cameras, and video capture systems save files as RGB and the conversion of RGB files to CMYK can be done in many ways. RGB converts to only CMY directly. However, when printing, we must add black ink and in doing so must cut back on some color. The Undercolor Removal (UCR) setup will help control this ratio so that a maximum ink density for the four colors will be 280-300% when printing on a coated paper printing stock.

Digital art that is comprised of spot colors (e.g., special colors: any colors that are not CMYK process colors), generally require conversion to the CMYK color space to enable file use. Because color gamut’s for spot color libraries, such as those associated with the PANTONE MATCHING SYSTEM, usually extend beyond the ranges of the CMYK color gamut, some spot colors may not be represented effectively using CMYK process inks.

In offset lithography, the density of CMYK inks can not be varied in continuous fashion across an image, so a range is produced by means of halftone screening. In halftoning, translucent CMYK ink dots of variable size are printed in overlapping patterns. Patterns are placed at different angles for each of the ink colors. Smaller halftone dots absorb less light; thus, as a result of an increase in the amount of reflected light, apparent density is decreased and the object appears lighter.

Halftoning screen angles (133lpi 40% screen enlarged)

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Wallpaper - troubleshooting problems & special papers

12/08/2007 by conrad.

Wallpaper edges and seams

To make sure the edges of paper are firmly stuck down, use a seam roller. Do not be too vigorous with this as it may damage the paper or leave a sheen on it, which will show when the paper is viewed from an angle. It is, however, not suitable for use on certain types of paper such as flock or embossed.

Air bubbles or blisters under wallpaper

Despite your best efforts to remove air from behind the paper as it is hung, you may find a blister remaining afterwards. There are two ways of dealing with this: Inject adhesive into the blister and use a seam roller to smooth it. Or, make a neat incision with a craft knife, and lift the edges enabling paste to be reapplied before smoothing back down.

Vinyl wallpaper adhesive

When hanging vinyl papers, you will need to use a special “vinyl to vinyl” adhesive along any overlaps, since vinyl will not stick to itself.

Pasting the wall

Some papers like Digimura, require the wall to be pasted rather than the paper. In this case, use a roller to apply the adhesive to an area slightly wider than the strip to be hung. This will enable you to paste the next section without having to work right up to the previous piece.

Embossed or relief wallpaper

Embossed papers need to be handled with care to avoid flattening the pattern – particularly at joins and corners. Many people prefer the durability offered by ‘blown vinyl’ relief papers.

Ready pasted paper

Ready pasted papers. You will rarely see professional decorators hanging this in the way suggested by the manufacturer, as it often leads to difficulties with misses or dry spots in the adhesive. They will normally paste it up as they would ordinary papers, but make their paste mix a little weaker to allow for the paste already on the back of the paper.

Fabric wallpaper

When hanging these, it is common to paste the wall rather than the fabric. By suspending the roll of fabric on a strong pole between two ladders, it is possible to work the fabric against the wall starting at the bottom. In this case you will need to smooth out upwards rather than down. Overlap successive drops (unless the edges are pre-trimmed) and cut through with a sharp knife, discarding the offcuts to produce a perfect joint.

To protect surfaces when smoothing, hold lining paper over the section to be smoothed.

Smoothing tips for wallpapering

Depending on the type of paper or material being hung, some professionals use a plastic spatula to smooth with. On strong surfaces, this is very efficient and dispels air from beneath the surface very speedily. It is an excellent tool for use with lining paper.

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Thankyou to our Wallpaper separation artists

26/06/2007 by conrad.

A big thank you goes out to all the separation artists who have worked with us over the last 12 months.

This is not only our digitally printed wallpaper artists but our spot colour separation artists for wallpaper too.
Coming in the next week……………..

How separations are done and what is the difference between separations for digital printing and separations for wallpaper and textiles

We uncover the myth of wallpaper separations and show an in depth demonstartion from start to finish.

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Our Smooth Range Of Substrates

17/01/2007 by conrad.

This is a heavyweight commercial wall covering specially developed for digital printing. It is non woven and allows you to paste the wall and not the paper. smooth in appearance, this product is identical to conventional wallpaper and you are hard pushed to tell the difference from digitally printed to conventionally printed.

Distribution by papergraphics

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Our Tactile Range Of Substrates

17/01/2007 by conrad.

This is a heavyweight commercial wall covering specially developed for digital printing. It is non woven and allows you to paste the wall and not the paper. Textured (Almost emboss like) in appearance, ideal for showrooms and reception areas.

Distribution by papergraphics

Usefull Links

Archive for the Technical Specs Category

Wallpaper Color Space Fundamentals

Wallpaper - troubleshooting problems & special papers

Thankyou to our Wallpaper separation artists

Our Smooth Range Of Substrates

Our Tactile Range Of Substrates

Wallpaper specifications and symbols