Kok-Wei Koh

MagCloud: magazine self-publishing for the long tail

In June of 2008, Hewlett-Packard Labs launched MagCloud, a print-on-demand web service for magazine selfpublishing. MagCloud enables anyone to publish their own magazine by simply uploading a PDF file to the site. There are no setup fees, minimum print runs, storage requirements or waste due to unsold magazines. Magazines are only printed when an order is placed, and are shipped directly to the end customer. In the course of building this web service, a number of technological challenges were encountered. In this paper, we will discuss these challenges and the methods used to overcome them. Perhaps the most important decision in enabling the successful launch of MagCloud was the choice to offer a single product. This simplified the PDF validation phase and streamlined the print fulfillment process such that orders can be printed, folded and trimmed in batches, rather than one-by-one. In a sense, MagCloud adopted the Ford Model T approach to manufacturing, where having just a single model with little or no options allows for efficiencies in the production line, enabling a lower product price and opening the market to a much larger customer base. This platform has resulted in a number of new niche publications - the long tail of publishing.

Pre-RIP color management for soft proofing

In an ideal situation, a color managed soft proof is generated by the same Raster Image Processor (RIP) that produces the final raster data for printing. In real-world scenarios, this soft proofing capability is often absent. To overcome this limitation, we developed a workflow using the Adobe PDF library for producing color managed soft proofs before incoming jobs from the web are sent to the RIP. This paper discusses color management challenges that presented themselves and how they were addressed. It also highlights a few specific cases where the separation into subsequent color management and transparency blending processes caused unexpected results and how they were dealt with. Such a system can be implemented as a cloud-based solution to provide end-customers with a quick, inexpensive and reasonably accurate preview of print products before the job is submitted.

A method to improve the invertibility of ICC profiles that use lookup tables

Traditionally, the AToB0 tag of an ICC printer profile, containing the perceptual transform from device specific to PCS Lab or XYZ values, has been generated directly from measurement data without considering the color re-rendering included in the PCS to device-specific transform found in the corresponding BToA0 tag. In this case, the AToB0 color conversion will often not be the inverse of the color conversion in the BToA0 tag. However, with ICC version 4, the AToBn and BToAn transforms are in general supposed to be inverses of each other, to the extent possible. This feature supports the re-purposing of color data within an ICC color management workflow. This inversion is a challenge for profile generation due to issues with either directly inverting 3-D interpolations or inverting every step applied in generating the BToA0 tag. Directly inverting a 3-D LUT may not be feasible because the forward mapping is usually not a one-to-one mapping. Mathematically, inverting every operation for generating a BToA0 tag may also be extremely difficult if not impossible. Consequently, a closed-loop method has been developed which iteratively adjusts AToBn tags to improve the invertibility of ICC profile transforms. The test results are very encouraging.