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View Full Version : Bump map gradient "steps" problem



alexoctagon
05-14-2008, 05:31 AM
Hi

I'm now doing a project where I need to zoom in on an embossed logo in a glass bottle. I noticed though that the steps of greyscale image are showing up like little ridges around it. I've changed the mipmapping to high and 2.0 which helps a little (any more than 2 makes it go a bit weird). This still isn't high quality enough though.

I've tried re-creating the image in Photoshop as a 32-bit file so there could be more greyscale steps and saving as HDR but it makes no difference. Short of trying to model this I'm out of ideas. Can anyone help me out on this?

Many thanks,
Alex

clagman
05-14-2008, 09:48 AM
to be honest you shouldn't need more than 8bpp in a greyscale image. Probably has more to do with the resolution of the image than the color depth. There is a balance to the resolution you render at and the distance the camera is the object/texture. To zoom in close requires a higher resolution image, so does rendering at a higher resolution. To do both you need a REALLY gigantic image.

tribbles
05-14-2008, 11:18 AM
I've tried that technique in the past - and I couldn't find a nice solution (except for modelling it properly, which is very time consuming).

If you increase the resolution, the steps will actually become more pronounced, as the vertical steps become more vertical.

I'm not sure how you're embossing it, but I'd use the image as a displacement map for a subdivided object (not sure about wrapping it around a glass bottle though). The displacement map can be adjusted - and you also won't end up with verticals. There'll also be an element of blurring involved too. But you might already be doing that (I've only done it as a flat object before).

clagman
05-14-2008, 11:26 AM
I wonder if a normal map wouldn't work better (aside from the displacement being the best way for sure).

alexoctagon
05-14-2008, 02:26 PM
Thanks guys. I've tried a displacement map but since the logo is text it consists of a lot of fine curves, even a heavily divided quad poly mesh isn't enough to create smooth curves around the rounded areas, instead it creates a kind of pixelated effect.

I've never created a normal map although I have been reading about it. Am I wrong but surely to do that I would have to model the embossed lettering first? Alternatively I believe there is a plugin that converts a bump to normal map, but surely since it came from a bump map it would have the same problem?

Surrealist.
05-14-2008, 10:58 PM
One thing that has not been brought up is how did you do the stepping of the gray scale image? There should be none. It should be a smooth transition. But Maybe you mean pixelization not stepping.

The other suggestion mentioned here not to overlook is the image size (resolution) not the bits. too low of a resolution image will give you the pixels mentioned above.

Then to do a displacement you can use SDS surfaces and let LW dynamically subdivide the object using the APS system. You'll find that in the Geometry tab of the Object properties panel.

The reason you are getting the jagged results can be from a) not having a high enough resolution image for that distance to the camera or b) not subdividing the mesh enough.

You can create a subdivided mesh (using the tab key) in Modeler. Just make a box with a few segments up and down and press TAB.

Then in layout to get a high enough resolution image in your displacement you can set Render Subatch Level to: Per Polygon about 100 or Pixels per Polygon about 10 or less.

For your logo, make sure the edges are not stepped but smooth. You can do this with the blur tool on the white logo over black BG in a paint program. (or invert the reverse if you wish)

alexoctagon
05-15-2008, 07:29 AM
Many thanks for these replies. I've been doing some tests - see attached.

Surrealist: Yes sorry, I did mean pixelization. I played around for ages with the displacement options, the best settings I found are shown. Although slightly better than the bump map, there are still rough edges around the outsides, this is highlighted even more on a glass bottle because the refraction and reflection accentuates it.

Regarding the bump map itself, I've found the same as Tribbles, if I increase the resolution of the image the problem gets worse. It's the same as the amount of subdivisions in the displacement options. I've shown how the bump image looks in Photoshop when viewed at 400%. The strips of gradient actually show up which I think is down to the bit depth.

I've been doing my job for 10 years now and I've come across this many times but got away with it because the embossing appears small. With this current job though it appears so large that I've got to deal with it!

(For interest my site is: www.octagongraphics.co.uk)

clagman
05-15-2008, 08:19 AM
I do get some pixelation when zooming in very close but I upped the resolution of the greyscale TIF image I am using for bump and it smoothed it out. We are talking about a really large image though (2500x800 pix).

Surrealist.
05-17-2008, 09:43 AM
Very close up I can actually see a bit of that banding in my displacement. But I also think yours has quite a bit more noise in it for some reason. The subtle banding I see does not look as bad. Are you sure there is not some extra noise in that image?