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Basically, the issue is that I am trying to map a graphics texture to a wall. I have prepared the graphics in a none 2 by 2 Aspect ratio. When I unwrapped the wall model all was fine as I have another texture which obeys the 2 by 2 aspect ratio. In my case it was a 512 X 512 pixel texture.

After which when I brought in the rectangular texture, the UV map appears stretched. I believed the editor saw that the image was longish it decidedly stretch the UV. However now the uv is showing my texture squished as the UV has been stretch in the Y axis.

To illustrate the problem this are the images.

enter image description here

Now, how do I make the uv not displayed as stretched when I change the texture?

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    $\begingroup$ I don't know if there is a mean to do that (apart scaling down), but UVs are relative values (percentages, between 0 and 1, even if you can place it "where you want"). For instance, this allows to scale or stretch the mesh to adapt to different images proportions. Maybe this is a convention or just a coherent way to make it work, but AFAIK there is no other way. $\endgroup$ – lemon Mar 17 '17 at 16:44
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add a material with an image texture node

  • in cycles, the uv unwrap "correct aspect" feature has a hidden requirement
    • your mesh must have a material assigned
    • the material must have an "image texture" shader node
    • select your image texture, with the funny aspect ratio, in the node
    • now cycles can find your image's aspect ratio
    • uv unwrap's "correct aspect" works again

it's a bummer that there isn't a notice in place, for the "correct aspect" feature..
something like warning: "unwrap correct aspect" cannot find image texture node

also, i found that adding a "texture image node" helped when i couldn't get texture painting to work — it was ultimately the same kind of problem

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I think I found a bug.

Unsatisfied with my online search on many forums regarding the matter. I have done a deep probe to the matter. But all the solutions were confusing and everyone seem to have their opinion to how that UV unwrap should work. It was clear to me the design was very strange if it's intended. It totally made no sense to how it behaved. What I have done is when ahead and download a much older version that is reputable to work properly with the least amount of issue. Version 2.66a. Afterwhich I appended all the models from 2.78b version which I created into the older clean install. And it worked as expected when I hit "Correct Aspect" during a uv unwrap operation.

And then it suddenly did not work again. I started to wonder why the behavior... and keep importing the different saves into different version of blender and then it works sometimes but other time it doesn't.

Finally, the issue was strange as it dawn on me ... when I turn on "Cycles Render" the UV unwrap operation does not work as expected! But when I switch back to the default "blender render" it worked again!

Clearly, this behavior is not intended as the UV unwrap tool is not working the same way in the 2 different rendering mode. The issue have existed since 2.66a till 2.78b.

We should report this bug.

Latest Update

I have created a bug report here. https://developer.blender.org/T50987 If anyone has the time to do the probe on your system, please confirm so that we know it's a consistent behavior over all machines and operating system so that we can update the bug report as need be. Thanks.

Steps to reproduce this Bug. (Do these in Default "Blender Render" Mode or "Blender Game" Mode)

  1. First Unwrap a simple box in a standard 2 by 2 default uv editor setup.
  2. Create a new 3 by 2 texture map file.
  3. The uv stretches in the uv editor accordingly with the newly created rectangular uvmap. (This is not the bug, it behaves as design)
  4. Now reapply Unwrap with "Correct Aspect" turned on, uv is corrected and behave as expected. UV map readjust itself to it now scale to the model's aspect ratio.

  5. Do those same 1-4 steps in "Cycle render" mode.

  6. You will discover that uv unwrap does not react with "correct aspect" turn on or off.
  7. It's as if "correct aspect" stops functioning in "Cycle render" mode.
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    $\begingroup$ See my answer about UV range I dont think it is a bug. As Lemon mentioned UVs are stored as percentage of the image size, if the image changes and the dimensions are bigger, then UVs stretch with it. $\endgroup$ – Duarte Farrajota Ramos Mar 18 '17 at 0:13
  • $\begingroup$ Did you read my Answer at all. Basically UV unwrap behaves differently when in different render mode. Did you try it on your workstation to comfirm before knocking it off? $\endgroup$ – hawkenfox Mar 18 '17 at 4:39
  • $\begingroup$ Yep, got the same result you did. Correct Aspect doesn't seem to have any effect under Cycles $\endgroup$ – Duarte Farrajota Ramos Mar 18 '17 at 5:13
  • $\begingroup$ Strange isn't it. While in "Blender Render" or "Blender Game" it works as expected. $\endgroup$ – hawkenfox Mar 18 '17 at 5:15
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    $\begingroup$ Developer's Archived the report commented - Yes, this is not a bug though the behavior is somewhat confusing. The Correct Aspect option works based on the image texture assigned to the mesh and visible in the 3D viewport, which is done through the material. For Cycles, the image shown in the image editor is decoupled from that. $\endgroup$ – hawkenfox Mar 18 '17 at 17:28

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