MacOS Tiff Thumbnail incorrectly clipped by alpha channel contents (OS Bug)

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  • Updated 3 years ago
  • (Edited)
Under Mac OS X 10.6.8 and PS CS6 (13.0.5), if I create a Tiff with layers (maybe the alphachannel is the problem) I got an thumbnail, which is showing only one layer, not the whole picture. If I flaten the image and delete alpachannels, the problem is gone, but this is not what i want.

My presets for saving allowing all, icons, windowsicon..... Least and sadly, my PS CS 5 is working fine, no problems.
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DET

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Posted 5 years ago

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Chris Cox

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Photoshop writes the composite image as the thumbnail, but Apple tries to read the TIFF and create it's own thumbnail. But Apple has longstanding bugs reading TIFF files with alpha channels (gets them confused with transparency). Apple's code does not know how to read layers.

Yes, the alpha channel is most likely the problem. Apple has fixed some of the issues in later OS versions, but has not yet fixed all of them.
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DET

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Thank you Chris,

but something had changed in creating thumbs by CS 6, cause my PS 5 is working fine, without this bug.

I have a new IMac and will prove if this behaviour occures on this machine.

On my "workinghorse" i have to delete PS 6, and will stay on PS5.
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Chris Cox

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Nothing has changed in the applications (though Photoshop CC has a change by not writing resource thumbnails anymore) or the files.

But MacOS has several known bugs in thumbnail building.

Why would you delete Photoshop CS6 over a minor OS bug?
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DET

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Hello Chris,

thanks for your answer, nothing has changed? The only thing that I know is that PS 5 did not have this bug on my Mac Pro, CS 6 has. Right, I don ́t have to delete it, only deactivate. Why? I am a professional photographer and my clients got mostly Tiff Files with layers, additional channels ... and in the least 20 years no one had a problem with my files. Till yet, a client called me and said "something is wrong with my files" :(. Okay, the files could be read, but they take a look at the previews and
see "strange" things and this is not professional in my opinion.
I just changed from 5 to 6 and thougt after a year on the market, there will be no surprises for me with this update.

My mainly used workingplace is a Mac Pro with the old 10.6, cause the third party software, for example for large format printers is very slow updated to the newest Mac OS sadly. So I stay a long time on old systems.

I am teaching at a university, I have bought new IMacs for the students and will see
what PS CS 6 will do on this machines, with 10.8.
Sooner or later I have to switch my own working stations to a newer Mac OS, or
windows ;), than I will use CS6, in the moment I take a brake.
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Chris Cox

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The TIFF files are the same written by Photoshop CS3, CS4, CS5, CS6 and CC.

The only thing that might have changed is your preferences for including thumbnails/previews, or your settings when saving the TIFF file.

But again, it sounds like you're just hitting a known bug in MacOS, and that affects all TIFF files with alpha channels regardless of what application wrote them. And again, that has nothing to do with which version of Photoshop you are running, just the MacOS version.
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Eric Dubois

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Sorry if this response is late. When Apple creates a preview, it uses the first channel after the color channel as an alpha channel, whether you want it to or not.

For example, if your channels are Red, Green, Blue, Alpha 1, Alpha 2, etc., Alpha 1 will be used to clip your preview. This is a Mac OS problem, not a Photoshop problem. It also affects PSD files.

The only workaround I found is to place an empty (completely white) channel in that position. Apple will still use it, but it won't clip your artwork.