Does DPI make a difference?

[SkiSouth]

Yes, in rendering DPI definitely makes a difference, especially with materials that appear to cause banding, such as brick and mortar. See the attached files. The 600 DPI image shows much less apparent banding than the lesser two images. If you take a lower DPI image and just "UP" the resolution, the banding is still present. Be careful of your final image. If banding occurs, the only way to rid yourself of the banding is to change materials /contrast colors or up the resolution of the output image. (or at least the only ways I'm aware of).

Note I was going to post a true size 800 DPI jpeg for your comparison, but the 4.5"x 4.89 in images was 7.5 Megs compressed, 38.6 Megs uncompressed. If you are planning on working with say an 8x10 at 800 DPI the image will be 145 Megs in size or so.

That being said, look at the slate roofs. There is the same patterning occuring, yet as there is no true color contrasts in the joints, the banding is not nearly as evident in any of the resolutions.

Hope this helps

[Scott Hopkins]

Skisouth,

Just out of curiosity, a few questions for you.

How long did it take you to do the same renderings at 800 DPI?

Once you made the 800 DPI rendering were you then able to shrink the file size back down in photoshop without the moiré effect reappearing? Having a bunch of 145 Meg files clogging up your hard-drive doesn't sound like much fun.

How big of a texture map did you use for your brick material? Approximately how many bricks? I wonder if having a better texture map would nip this problem in the bud.

[LRaiz]

One thing to keep in mind is that DPI is not the only factor that affects banding. Image size (in inches) is just as important. If you increase the image size while maintain the same view angles and same DPI then banding will decrease. Or conversely if image size increases then it is possible to decrease DPI and still maintain the same amount of banding. This is all understandable since the resulting number of rays-traced pixes is computed as a product of DPI and image size. At the end of the day the proper choice of DPI is somewhat of an art and comes with experience.

[SkiSouth]

Skisouth,

Just out of curiosity, a few questions for you.

How long did it take you to do the same renderings at 800 DPI?

From the hidden line image to hidden line image (having saved the file etc) it took 40 minutes to generate the image at 800 DPI. Probably half that for 480 or 600 DPI.

Once you made the 800 DPI rendering were you then able to shrink the file size back down in photoshop without the moiré effect reappearing? Having a bunch of 145 Meg files clogging up your hard-drive doesn't sound like much fun.

Yes, you can reduce the image and it hold the non-"moire" effect. See the attached it is the image at 300 DPI (reduced in Photoshop from 800 DPI)

How big of a texture map did you use for your brick material

2.4 Meg jpeg file 2688x1344 pixels

? Approximately how many bricks? I wonder if having a better texture map would nip this problem in the bud.

The image was generated using the ACME brick image file generator - It is 16 courses high and 10 and a half bricks long.