Why does Photoshop image change when flattened?

[Kent Shafer]

<p>I have a 16-bit grayscale image in CS3 consisting of three layers: background + two curves adjustment layers. When I flatten it, the contrast changes. (The top layer, which brightens the outdoor portion of the scene, becomes less effective, though it still has some effect.)</p>

<p>This is the first time I have run into this, though I see there was a thread on the same problem back in May 2005: <a href="http://www.photo.net/digital-darkroom-forum/00BMU6">http://www.photo.net/digital-darkroom-forum/00BMU6</a>. Nobody seemed to have a solution at that time.</p>

<p>Does anyone know how to avoid this effect? Or is it just a quirk we have to live with?</p>

<p>I'm attaching a screen shot showing the layers.</p>

<p>Thanks.</p><div></div>

[w. shinn ii]

<p>I too have experienced some strange/unpredictable results as a result of editing images after applying adjustment layers. To avoid this, I've developed a work flow which involves image edits before curves, level and color adjustments. This seems to work the best for me.</p>

 

[Tim_Lookingbill]

<p>See if it does this when you merge the top layer first with the one just above the background, then merge the subsequent single layer with the background layer afterward. I've seen this occur as far back as PS 7 and not sure what causes this, but I could be wrong about this with regards to your version of Photoshop.</p>

<p>You might even try merging the layer just above the background first and then merge the top layer second. In other words in reverse order.</p>

[Kent Shafer]

<p>Merging the background layer with the curves layer just above it makes the outdoor portion of the scene (the one lightened by the top curves layer) even lighter - that is, it makes the top curves layer have a more powerful effect.<br /><br />Merging the background layer with the top curves layer, on the other hand, makes the outdoor portion darker - that is, the top curves layer has less effect.<br /><br />And finally, merging the two curves layers together makes the outdoor portion much darker. As far as I can tell, it completely eliminates the effect of the top curves layer.<br /><br />I may have found a clue though. All of the above was viewing the image at 12.5%, which made it fit nicely on the screen. If I switch to a 100% view, merging the background with either curve layer has no effect, and flattening has no effect either, though merging the two curves first still does. It must have something to do with the moire effect created by the pattern in the screen door.<br>

<br />Thank you for the suggestions.</p>

[steven_clark]

<p>Might be a quirk of when it does its resampoling in the blending process. Sounds like the display behavior outside 100% is incorrect before flattening.</p>

[Kent Shafer]

<p>Thank you Steven. Yes, that seems right.</p>

[kyleweems]

<p>PS has lots of visual bugs it seems.. always has.. I believe Steven is correct.<br>

However, you might try 'stamp visable' before flattening to see if that helps eliminate it. Hit cmd+alt+shift+e (mac) or ctrl+alt+shift+e (pc) ...aka, the entire left side of your keyboard. Make sure you have the top layer selected.. it will put everything together on a new top layer.<br>

Just something to try perhaps<br>

Kyle</p>

[Kent Shafer]

<p>Thanks Kyle. I did try it. At 12.5% view, the new top layer looks dramatically different than the layer stack did before the ctrl-alt-shift-e maneuver. But at 100% view, they look the same.</p>

[kyleweems]

<p>Another thing to consider.. up until CS4, photoshop has some weird things with any sort of odd zoom level.. most noticable is the pixelation around the edges and in fact within the image itself. Levels other than 25, 50, 75, 100, etc. are subject to the result of weird issues with the math that calculates the image and does the zoom. Just recently with cs4 they finally smoothed all of this out and made it work properly.. only took 15 years or so :) This may be what's happening, as those zoom levels do all sorts of wacky things.</p>

<p>Kyle</p>