Morphography tutorials
The Great Bump Map Disaster
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• Introduction

So, what exactly is the great bump map disaster? When the PC version of Poser 3 or 4 converts a graphic file (.BMP, .TIF, .JPG) into a bump map (.BUM), it does it wrong. In a lot of cases, this doesn't matter; or it just looks "a bit wrong". Sometimes, like when you really need it, it is obviously wrong; see below for an example.

The Macintosh version of Poser 4 does not display this problem, and later versions of Poser from Pro Pack through to 5 and 6 don't use the .BUM format. However, if you download bump maps which have already been converted to .BUM (rather than in .JPG format which is the norm), you should try to find out what system did the conversion since those produced by a PC will be wrong. If you can't find out, follow the instructions below and try both versions to see which is best.

This problem was first pointed out by gillan on the Renderosity forum. You can probably still read the thread here: Bug in poser bump mapping and solution Since then, MartinC (a Mac user, ironically) has unofficially taken up the cause. All credit should go to these people; I'm just passing on what they've found.

• The Problem

Here's a very simple bump map:

The white area should produce the effect of a "sticking out" disc. But surprise surprise, if we let Poser convert this, it doesn't look right.

On the left, a simple square with our bump map applied to it; on the right, an actual cylinder poking through a square to show where the light is really coming from. As you can see, the bump mapped version is about 90 degrees out. It should look like this:

Now read on to find out how to do it.

• What to do about it

You'll need an image editing program which can handle the red, green and blue colour channels separately; I originally used Paint Shop Pro 5, but the general method is applicable to later versions of PSP, and others such as Photoshop.

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