Incorrect UV moving/scaling

Hi all,
I am editing a car model; it has a 1024x1024 px UV mapped texture, and I have resized it with GIMP Lanczos3 interpolation to 1536x1536; in order to add some details to the car, I have edited the texture file, resizing the image surface to 2048x2048, but keeping the image’s content to 1536x1536; having moved the content to the upper-left corner, I now have a half of a free border of 512 pixel on the right and on the bottom.
To make the thing clearer, the attachment is how the texture looks like now (seen with the website background it’s not very clear - I suggest you download it, it’s 741 bytes).

Now, of course I had to move and downscale the UV; a bit of maths suggests to downscale by 0.75 and to move it 256 pixels up and left. In fact, exporting the UV to .tga in 2048x2048 and downscaling it produces a perfect result on the texture. But in Blender, the result is slightly wrong, that is, the final UV is not perfectly centered, it is clearly different from the GIMP result with the.tga. This would be easy to fix if I had only one UV, but actually the model has to stay divided into 15 objects.
Any suggestions?

Thanks,
Ocirne

Attachments


Your attached image turns up black? And i cant click it either. I don’t quite understand what you are trying to achieve? Can you post a screenshot of your blend? :slight_smile:

Yes, the attachment isn’t the real texture file, but only a mock-up that shows how the real texture is made: the black part is where is the original texture, and the white part shows the white border I have created, where I will put additional texturing. However, I have created more media:

img62.imageshack.us/img62/6448/seatcomplete.jpg

This is the result in GIMP; as you can see, the UV fits perfectly.

img832.imageshack.us/img832/5690/seatblenderuv.jpg

This is the screenshot form Blender; the UV is slightly moved towards the upper-left corner, and this produces a terrible rendering output.

To create the first (GIMP) picture: I have started from the texture, then I’ve imported the UV (previously exported from Blender as 2048x2048 px) as a layer, I have downscaled it to 1536px and moved it to the upper-left corner (a movement of 256px), to place it exactly on the texture.

To create the second (Blender) picture: I already had the UV, so I set as texture the same picture as for GIMP, and then downscaled the UV by 0.75 (1536/2048=0.75) and moved it 256px towards the upper-left corner, with exactly the same movement I had used in GIMP.
But the result is different!

Ocirne

How are you scaling the UV in blender? Just scaling, then moving? If you are just scaling them, then the UV islands are scaling around their median point. I think I would position the 2d cursor in the UV layout window to the upper left corner of your work area. Set the pivot point the be the 2d cursor and then scale. Everything should then scale towards the cursor, scaling and moving your UV layout at the same time and should work. Sorry, I’m rendering right now so I can’t test it out… but from your images that what it looks like is happening…

Randy

Randy,
you are awesome! It’s worked perfectly, without even needing to move after scaling!
Many, many, many thousands thanks - I can now continue my work!
I’ll be eternally grateful to you - well, at least for a couple of weeks :smiley:

Thanks a lot,
Ocirne