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From: "Joris Van Damme \(AWare Systems\)" <info@awaresystems.be>
To: <zhangweiwu@realss.com>,
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Date: Wed, 25 Feb 2009 10:45:00 +0100
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Subject: Re: [Tiff] OT: Text layer possible in tiff format?
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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 hi=EBrarchical. 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 th=
e =

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 th=
e =

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 =

hi=EBrarchy in the intended manner. Obviously, not everybody believes in th=
e =

all-round long-term benefit of unlocking the user's data, ensuring =

interchange and enabling long-term storage.

Best regards,

Joris

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