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ahrumh58723069
Participant
May 24, 2020
Answered

Accurately previewing zoomed out halftone

  • May 24, 2020
  • 2 replies
  • 1755 views

Has anyone figured out a solution to the problem described in this post:

https://community.adobe.com/t5/photoshop/flattening-image-changes-it/m-p/9021449

 

I frequently work with large images that are either halftoned or have a threshold adjustment layer applied. I understand that the image is only pixel accurate at 100% zoom, and that when I am zoomed to 20%, Photoshop is showing me an interpolated preview. This (partially) explains why, when I am zoomed out, images sometimes shift dramatically when they are flattened (I still don't understand why Photoshop interprets the zoomed out preview one way when it is layered and another way when flattened).

 

I find the zoomed out image previews are much more accurate to the print after they are flattened. Unfortunately, I can't fiddle with my adjustment layers and touchup layers when the image is flattened (obviously). Is there any way to preview the zoomed out image in its flattened appearance without having to actually flatten the image? Checking my work at 100% is great, but you can't really get a sense of what's going on in the overall image on my files at 100%.

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Correct answer ahrumh58723069

Oh! I solved it. Posting my solution here if anyone needs help with this same problem. If you create a smart object with a layer and all it's active adjustment layers, the smart object will render as the same as if the whole image were flattened. It's not a perfect solution, but it works well enough and is better than continually flattening a copy of my document to check my work.

2 replies

D Fosse
Community Expert
D FosseCommunity Expert
Community Expert
May 24, 2020

That's actually a pretty good and useful workaround.

 

Yes, you understand what's happening when zoomed out. But it goes deeper. Not only is the preview itself interpolated - but the actual adjustments are previewed as such too. So with halftone dots, the preview presents you with a calculation based on all those halftone dots being blurred into medium values. The result of the adjustment calculation is dramatically different from an adjustment based on the full data.

 

In other words, the preview can be very misleading.

 

This is an ancient problem that produces puzzled posts here at regular intervals. Why does the image change when I flatten? No, it doesn't, it was just an inaccurate preview at an odd zoom ratio.

 

Originally this was done to help performance. One could argue that today's hardware should be able to work with the full data at all times. But this is probably too deeply embedded in Photoshop code to easily change now. Theoretically, setting Cache Levels to 1 should do just that, but at least at the moment that's not possible. It snaps back to a higher level.

    davescm
    Community Expert
    davescmCommunity Expert
    Community Expert
    May 24, 2020

    I thought about the modern hardware aspect Dag, but it may still not be possible. Imagine a Gigapixel image with multiple layers and every one of those pixels needing to be re-calculated live as you move an adjustment slider. That is what a full preview would need to cope with. The current system only needs to recalculate the screen window pixel size.

    It would be good to have a switchable option though, so that on more reasonable image sizes it blended all pixels and if performance slowed to unacceptable levels the option would be to switch back.

     

    Dave

      D Fosse
      Community Expert
      D FosseCommunity Expert
      Community Expert
      May 24, 2020

      Yes, you're probably right. As hardware gets faster, file sizes get bigger. It's the Red Queen effect.

       

      (That's Lewis Carroll for those not familiar with it:

      "Well, in our country," said Alice, still panting a little, "you'd generally get to somewhere else—if you run very fast for a long time, as we've been doing."

      "A slow sort of country!" said the Queen. "Now, here, you see, it takes all the running you can do, to keep in the same place. If you want to get somewhere else, you must run at least twice as fast as that!")

        A
        ahrumh58723069AuthorCorrect answer
        Participant
        May 24, 2020

        Oh! I solved it. Posting my solution here if anyone needs help with this same problem. If you create a smart object with a layer and all it's active adjustment layers, the smart object will render as the same as if the whole image were flattened. It's not a perfect solution, but it works well enough and is better than continually flattening a copy of my document to check my work.

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