2009.02.25 09:45 "Re: [Tiff] OT: Text layer possible in tiff format?", by

Zhang,

Recently I had a talk with a photoshop user who showed me how to save an image from Photoshop into TIFF format with all layers preserved. I think this makes TIFF a good image exchange format for users of different photo manipulation software. If it can support text layers, it would be even better, because most of the times people exchange retouched photo only need to preserve layers (including text layers) but do not need to preserve all masks and paths. Since TIFF is usable for non-professional users as well (both Linux and Windows can view and print these files without using image manipulation software), it makes it idea for exchange not only between people who do image manipulation but also people who receive & use the result.

In the past, people who manipulate photos has to ask if the other one want layered format (PSD, ideal for professional users but not viewable to ordinary users) or ordinary image (JPEG, readable to ordinary users but lost layer information for professional users), with TIFF they don't have to.

I agree 100%, except that I don't feel it's off-topic.

TIFF is extensible, and hiërarchical. Which means tags can be defined to mean LayerIFDs similar to SubIFDs, tags can be defined to specify text content of an image IFD, etc. Its philosophy of enabling readers to always safely ignore what they don't understand makes for good interchange. It means that an image IFD with text content, can include the text with position and style and such in a special tag for those that can make sense of it, but should also include the pre-rendered text as a plain image in the strips or tiles such that software that only understands image still offers the same result though with limited functionality (i.e. no search nor editing of text). And it means that IFDs that have a LayerIFDs tag, should still contain the pre-rendered 'flattened' version, such that software that doesn't wish to bother with the concept still shows the image, though with limited functionality. Its philosophy includes loss of information that software cannot make sense of, and that guarantees consistency of data. It means that software that doesn't understand layers and allows editing of the flattened base IFD, should not resave the LayerIFDs, and data cannot become inconsistent.

TIFF would be ideally suitable for image interchange. It could mean to image, what RTF never succeeded in meaning to text. It could be the user's guarantee that his image data with all its advanced functionality flows freely. However, then there's reality. The vendor of the industry standard image editing software, that also owns the TIFF specification, saves any advanced data in TIFF in private tags instead of extending the TIFF hiërarchy in the intended manner. Obviously, not everybody believes in the all-round long-term benefit of unlocking the user's data, ensuring interchange and enabling long-term storage.

Best regards,

Joris