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Image Processing and Workflow RAW, DNG , TIFF and JPG. From Capture to Ready for Publish/Display. All software and techniques used within an image workflow, (except extensive retouching and repair or DAM).

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Old June 16th, 2011, 12:19 PM
Doug Kerr Doug Kerr is offline
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Default The amazing TIFF file

As many of you know, I have not so far been a big user of Photoshop, and so I'm unaware of many things that pertain to its world.

A while ago, I was surprised to learn (from Bart) that a TIFF file could in fact hold the layers that are such an important part of the Photoshop milieu.

More recently, I was even more surprised to learn (from Bart, again) that in fact a TIFF file could support almost all (maybe really all) the functionality of Photoshop's proprietary document format (e.g., PSD files and their cousins).

Not that I didn't fully believe Bart, but of course I always like to experience these things for myself, so I soon build a monstrous layer cake in PS CS5. It had multiple image layers; pixel and vector layer masks; adjustment layers (clipped to the layer immediately below and not), pone of which was a Curve layer with a very peculiar (and thus recognizable) curve; that arch-preculiarity, a Clipping Mask; and a Work Path and a couple of named paths.

I saved this monstrosity as both a PSD file and a TIFF file and then closed the working document.

I loaded both its PSD and TIFF spawn, and I couldn't find one iota of difference between them. The curves as displayed looked identical (and they were way peculiar).

Way amazing!

Next, I though I would become a bit more global, and looked at moving the TIFF files between PS and my other editor, Picture Publisher 10. Of course in the PS to PP direction, the composite image showed up. PP doesn't really have any layer capabilities, so of course none of that structure was visible.

In the other direction (PP to PS), I fond something quite interesting.

In PS, when there is no selection in place, there is no selection mask; that it, it is not as if there is a selection mask with nothing selected (transparent nowhere), nor a selection mask with everything selected (transparent everywhere).

But operations that are controlled by a selection mask (where present) mostly act as if the mask were there with everything selected. That is, a Fill operation fills everything, or a direct adjustment adjusted the entire image.

Picture Publisher does not have Photoshop's arsenals of masks. It only has one kind, which is essentially its Selection Mask. But' as with Photoshop, "no selection made" does not mean there is a Selection Mask that is everywhere selected (transparent). But, also like Photoshop, if there is no selection made, many operations (fill, adjustments, etc.) have the scope as if there were a Selection Mask with everything selected.

None of this should be surprising.

If we look at the mask channel when there is no selection made, it is all black, suggesting that the Selection Mask is everywhere opaque, but that's not really true. In fact, the system acts (as I said above) as if the Selection Mask, if present, is everywhere transparent.

Now what is interesting is when we export an image as a TIFF file. There, PP gives us the option to Save Mask Channel or not.

If I have not made a selection, the Mask Channel is everywhere opaque (in according with what I described above). Suppose I set Save Mask Channel to ON. (You can't do this with no selection made; if we want to test this with no selection made, we must make an arbitrary selection, start a Save As TIFF, set that option in the Options dialog, exit that dialog, abort the Save As, and clear the selection.

But suppose I have Save Mask Channel set ON, have no selection made, and do Save As TIFF. What do we get?

Well, the Mask Channel is all opaque (even though it doesn't do anything in the program with no selection made) and is evidently saved as such.

I look at the TIFF file with my general-purpose viewer (VuePrint). It shows the entire image. It doesn't understand the mask channel (even one that reflects a selection).

I look at the file with my browser. It shows the entire image. It doesn't understand the mask channel (even one that reflects a selection).

I look at the file with Photoshop. The display is "the great empty beyond" ("all pixels transparent through the entire image stack" - of course here there is only one layer. Evidently it understands the mask channel (well, I would think!), finds it completely opaque, and shows none of the image.

BreezeBrowser does the same.

Again. no real surprises.

I think the caution is to be careful, when emitting TIFF files from "other" applications, to be sure we know what their behavior is with regard to the mask channel, if they have such a thing, in the case where we hadn't intentionally "made one".

Otherwise, we (or someone to whom we send a TIFF file) may wonder just where the image went.

incidentally, when I import this file into Photoshop, and of course can't see the image, I haven't found any way to "change the mask channel" to see the image. It almost seems as if it is taken into account at import rather than being actually taken in as a mask. (I don't find anything, for example, in the Channels panel that seems helpful).

Best regards,

Doug
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Old June 16th, 2011, 10:55 PM
Jerome Marot Jerome Marot is offline
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Default

TIFF stands for tagged image file format which describes its functioning pretty well: it is just a container for data structures designed by tags. That makes it powerful, expandable and a nightmare of incompatibilities. Beware of tiff files: more often than not, if your application does anything a bit complex with it another program will not be able to read the data correctly. Developers believe they agree on what the tags mean and what data structure should be associated to a given tag, but they don't.
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Old June 17th, 2011, 04:43 AM
Doug Kerr Doug Kerr is offline
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Default

Hi, Jerome,
Quote:
Originally Posted by Jerome Marot View Post
TIFF stands for tagged image file format which describes its functioning pretty well: it is just a container for data structures designed by tags. That makes it powerful, expandable and a nightmare of incompatibilities. Beware of tiff files: more often than not, if your application does anything a bit complex with it another program will not be able to read the data correctly. Developers believe they agree on what the tags mean and what data structure should be associated to a given tag, but they don't.
An excellent caution. Thanks.

Best regards,

Doug
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