UV unwrap "Correct Aspect" stop functioning in Cycle mode 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.



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