Flattening an image--very puzzling

[mdijb]

I have an image with 9 layers above the backround layer.  The layers are for making adjustments to make a print.  When I flatten the image, there is a visible change in contrast that occurs, or other tones that should not be occuring.  I have tried everything to figure out why such a change is happening and am stumped.  There should be no change at all.  Can anyone help??

MDIJB

[alanrew]

Is this image 8 bits per channel or 16 bits?

What you see before flattening the layers might just be a preview i.e. an approximation of the result, for performance reasons. After flattening the layers, PS might then be re-calculating the preview to give the 'exact' pixel values. With an 8 bits per channel image, lots of cumulative/compounded changes via layers might cause loss of precision due to the small number of bits to work with, & then flattening the layers is exposing this loss by showing you the actual result rather than a preview of it.

Just my two penn'orth.

HTH

Alan

[Tim Gray]

I've experienced that, but was never able to diagnose (maybe smart objects?).  You can try this to alleviate the problem with  (windows) ctrl alt shift w (or e if I'm misremembering) will merge all the layers and create a new pixel layer at the top of the stack. If I recall correctly the appearance of this layer doesn't change.

[mdijb]

I have tried that, and also merging all visible layers with the same, frustrating result.

Printing thei mage with all the layers is accurate--just the flattening is the problem

I am working on an 8 bit image
MDIJB

I've experienced that, but was never able to diagnose (maybe smart objects?).  You can try this to alleviate the problem with  (windows) ctrl alt shift w (or e if I'm misremembering) will merge all the layers and create a new pixel layer at the top of the stack. If I recall correctly the appearance of this layer doesn't change.
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[bryanyc]

I have tried that, and also merging all visible layers with the same, frustrating result.

Printing thei mage with all the layers is accurate--just the flattening is the problem

I am working on an 8 bit image
MDIJB
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hmmmmmm.....

sometimes it has to do with 100% viewing.  If you flatten in 100% view do you still see the change?

[perbernal]

hmmmmmm.....

sometimes it has to do with 100% viewing.  If you flatten in 100% view do you still see the change?
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Try to flatten each layer from the bottom of layers list instead from the top.

[alangubbay]

I have an image with 9 layers above the backround layer.  The layers are for making adjustments to make a print.  When I flatten the image, there is a visible change in contrast that occurs, or other tones that should not be occuring.  I have tried everything to figure out why such a change is happening and am stumped.  There should be no change at all.  Can anyone help??

MDIJB
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I have come across this problem several times in the past and it did cause some difficulty.  It does not occur now because I tend to merge layers as I go along and only keep layers seperate if the intention is to finally archive the image that way.

Do not flatten the image in one go but try merging layers one at a time to see where the trouble occurs.  Sometimes it helps to change the order of some layers, where this is feasible.  At least, you may be able to get your image down to 2 or 3 layers without change.  If you must then finally flatten it, perhaps it will only need a little further work to get back what you originally intended. Usually I managed to find a reasonable compromise one way or another.  Best of luck.

Alan

[BobDavid]

You may have been in "soft proof" mode prior to flattening. After you flatten, Photoshop turns off soft proofing.

[mdijb]

Just a guess... some adjustments (layers) look a little different at anything less that 100% view. When you flatten while viewing at, say, 33%, the display might appear to change.

So as a test, set your view to 100%, then flatten, and see if you notice any change.


BINGO!!

I tried your suggestion and when flattening at 50% viewing or greater, no changes in screen appearance occur.  At less than that, changes begin and at 12.5 % viewing the changes were greatest.  My image was 20x28 so viewing at this small size was needed to get it on my screen.  

Thanks for the suggestion!!

MDIJB