US 2014/0354726 A1
Multi-layer printing on non-white backgrounds
Electronics for Imaging, Inc.
When printing on to a clear or coloured substrate it is normal to print a white layer, then print the image on top. However printing on to a bright white can require extra coloured ink to achieve full image density. Unfortunately the extra colour ink may lead to gloss banding effects.
The proposed solution is to print with the white layer a proportion of the coloured image 31, then the remaining part of the colour image in the second pass 32. For instance 20% of the colour image may be printed with the white layer. Where colour ink will be printed less white is deposited, so that the total amount of ink laid down in the first pass is constant. The colour ink is printed into the white layer while it is still wet, and then the first layer is cured. The image is not particularly visible in the white layer at this stage. However, when the main part of the colour image is printed on top the colour density is higher than it would be if printed on a plain white layer, without loss of detail.
So instead of having to increase the amount of colour ink in areas of high image density to increase the saturation when printing on a uniform white layer, the amount of white ink is reduced in the areas of high image density.
There are other embodiments proposed. Instead of part of the colour image being printed with the white layer, only black or light black ink is used. This saves ink as only black is used, but the saturation is not quite so high. It works well in dense shadow or dark areas of the image.
The amount of the colour image printed with the white layer can also be varied according to the image or part of image. For instance where a photo appears, 60% of the colour image is printed with white, where a graphic appears 40%, and with text 0%.