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A
AsherAtSD
Participating Frequently
December 22, 2023
Answered

"Blend If" Merge Fails - Changes Image [Locked for abusive comments]

  • December 22, 2023
  • 19 replies
  • 351 views

"Blend if" works to separate luminance ranges as expected— until flattening, at which point all work is destroyed. 

 

To reproduce with any image:

 

1. Convert layer to smart object.

2. Duplicate and smart object and create a group for each. 

3. Set blend if for group 1 to 0-127 and for group 2 to 127-255

4. Merge either group. 

5. Image changes (and should not). 

 

Someone please explain why this is happening and how to avoid it. 

This topic has been closed for replies.
Correct answer D Fosse

View at 100% and check again.

 

Whenever something seems to change when merging layers, it's because you are not viewing at 100%. The merged result is correct. The preview is misleading and incorrect.

 

100% has nothing to do with size. It means one image pixel is represented by exactly one physical screen pixel.

 

For performance reasons, all blending and adjustment previews are calculated on the on-screen version of the image. When you are zoomed out, that means a resampled and softened version of the image. Pixel levels are averaged out. You get a lot of intermediate values that aren't there in the full original data.

 

When you merge, commit an adjustment etc, the numbers are re-calculated on the full original, pixel for pixel.

 

Viewing at 100% avoids all this and renders the whole issue moot. You see every pixel before and after, and so nothing changes.

 

---

 

You might argue (and I wouldn't disagree) that with todays hardware, it should be possible to always work on the full data instead of a cached smaller version. Previously it was possible to set Cache Levels to 1 in Preferences and do just that, but in later versions that's not possible. Whether bug or intentional I don't know.

19 replies

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A
AsherAtSDAuthor
Participating Frequently
December 22, 2023

And if Photoshop is simply incapable of handling this WYSIWYG, why is that not considered to be a major show-stopping bug?

A
AsherAtSDAuthor
Participating Frequently
December 22, 2023

Separately from the bug, what are recommendations for resolving the zoom-level issue when working with extremely large files, for example 24" square @ 720dpi?

 

Is Photoshop simply incapable of handling this situation WYSIWYG?

A
AsherAtSDAuthor
Participating Frequently
December 22, 2023

It seems that zooming to 100% fixes it in the preview (as suggested), exporting at 100% fixes it in the result image, but exporting with scaling includes the artifacts.

 

That is clearly a bug— and one that seems to reveal the issue at hand. 

 

  1. It seems that D Fosse was correct about it being a preview issue, while I was also correct that it should never be a preview issue because nothing about the image changed.
  2. There is a bug in Photoshop that results in artifacts being generated when this particular blending occurs at certain scales. This is not an incidental effect of an applied algorithm working differently at different scales; it is a bug in Photoshop's blending algorithm at particular scales, as nothing in the image has changed, and no scale should see a different result when blending (every scale should have a successful blend of a luminance separation). 
davescm
Community Expert
davescmCommunity Expert
Community Expert
December 22, 2023

I've just tried the exact steps you describe here (viewing before and after at 100% zoom) and there is no image change.

Please  attach a link to a psd that demonstrates the issue, so we can try it on another system

 

Edit to add: By by using double groups, as per your screenshots, I could see some artifacts when zoomed out. But using Ctrl+1 to zoom to 100% showed they are preview only and there were no artifacts at 100% zoom wich is the actual image blend. (those artifacts also disappeared when merging all layers and groups, proving they are preview only.

 

Dave

    A
    AsherAtSDAuthor
    Participating Frequently
    December 22, 2023

    Layers are screenshots, images are exported.

    A
    AsherAtSDAuthor
    Participating Frequently
    December 22, 2023

    Layer Setup:


     

    Image Setup:

     

     

    Merge Group:


     

     

    Image Result:

     

     

    Issues with result:

     

    D Fosse
    Community Expert
    D FosseCommunity Expert
    Community Expert
    December 22, 2023

    In that case it might be helpful if you showed before and after screenshots. And yes, make those screenshots at 100%.

    A
    AsherAtSDAuthor
    Participating Frequently
    December 22, 2023

    You clearly didn't read my post. 

     

    This has nothing to do with preview level. No modifications were applied to the image.

     

    When one of the two groups is merged, the image is no longer blended properly. 

     

    Your post is entirely irrelevant and not helpful. Please read first next time.

    D Fosse
    Community Expert
    D FosseCommunity ExpertCorrect answer
    Community Expert
    December 22, 2023

    View at 100% and check again.

     

    Whenever something seems to change when merging layers, it's because you are not viewing at 100%. The merged result is correct. The preview is misleading and incorrect.

     

    100% has nothing to do with size. It means one image pixel is represented by exactly one physical screen pixel.

     

    For performance reasons, all blending and adjustment previews are calculated on the on-screen version of the image. When you are zoomed out, that means a resampled and softened version of the image. Pixel levels are averaged out. You get a lot of intermediate values that aren't there in the full original data.

     

    When you merge, commit an adjustment etc, the numbers are re-calculated on the full original, pixel for pixel.

     

    Viewing at 100% avoids all this and renders the whole issue moot. You see every pixel before and after, and so nothing changes.

     

    ---

     

    You might argue (and I wouldn't disagree) that with todays hardware, it should be possible to always work on the full data instead of a cached smaller version. Previously it was possible to set Cache Levels to 1 in Preferences and do just that, but in later versions that's not possible. Whether bug or intentional I don't know.

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