Re: Need OPI support for tiff images with transparencies
Just to clarify, if you use TIFF with a clipping path to hide the background, a proper OPI solution like HELIOS ImageServer supports TIFF/PSD images with a clipping path and the OPI resolved output will be correct – the background will be clipped away. In case the clipping path works for you the following information can be skipped.
Using transparent background images with OPI entails the following problem: Most OPI resolvers basically replace the OPI referenced image with its original image, usually during the PostScript generation. PostScript does not support transparency in color images, so using PostScript you will always receive image data with a white background. Only PDF supports transparent color images.
Using InDesign CS2/3 with placed transparent PSD or TIFF images introduces another problem inherent to InDesign: it writes no OPI comments for transparent images and embeds the placed image into its PostScript or PDF export. So no chance to generate OPI comments for transparent images here. By default, HELIOS OPI generates non-transparent low-res/layout images, which means the customer will not fall into this InDesign limitation.
Even with the current HELIOS PDF-native OPI solution, transparent images will not work because InDesign will not create OPI comments and the HELIOS PDF-native OPI resolver does not support an alpha mask for transparent images. To use transparencies within InDesign, e.g. drop shadows, assign transparency to an image box or objects within InDesign, etc. This is no problem with PDF-native OPI, only transparent background placed images will not work.
Using XPress, there is no change to use transparency in the output because XPress will flatten its generated PostScript/PDF file so that there is no transparency available anymore. This can also be verified placing the XPress generated PDF again and you will get no transparency against the background.
And now the good news: HELIOS is working on a solution to support transparent images with InDesign and the HELIOS PDF-native OPI, details will be promoted when available.
Regarding the need of OPI within InDesign, I know customers who use 500 MB image data on a single document/page where high-res PDF exporting on a 3 GHz Mac or Windows workstation takes 25 minutes. Using PDF-native OPI, the client is released in a few seconds.
Remote users will also benefit from OPI by working with low-res files. Another good reason for OPI would be re-purposing images from a central image server/library and moving the ICC color separation to the server with central settings instead of individual settings for each image within the document on each client.