article covers how we can achieve better visual textures for games
while still keeping to low memory footprints, thanks to efficient
management of the visual results of texture compression. We will learn
in-depth what type of visual results we can expect, and examines the
use of the hardware DXT compression method. [Please note that the
example textures can be clicked on to see higher-resolution versions of
Handy tools for this study:
To view, load, and save DDS textures, the following tools and resources are handy.
Developer.Nvidia.com has a set of tools for Photoshop to create and save DDS / normal maps.
WTV Viewer and DDS Thumbnail Viewer
(provided by NVIDIA) are small and fast viewers that allows you to
scroll through the folder images in explorer view and see the alpha of
www.irfanview.com lets you quickly and easily read, scroll through and thumbnail the DDS images.
As we go through this article, we will be using NVIDIA's DDS Photoshop tool, as seen in Figure 1.0.
note that there are several other programs out there, including
freeware, that will do the same task, perhaps with a better or worse
result. As NVIDIA's DDS tool is commonly used within the industry, we
will base the result from this article around its quality output.
DXT / Compression:
Throughout this article we will mainly concentrate on DXT1, as it the
most useful format due to its effective memory size - a 1024*1024
texture is only 603KB in size. With a compression ratio of 1:8, DXT1
keeps the memory size low by using an algorithm that divides up the
texture into 4x4 pixel blocks, where each block only stores 2 unique
colors in the combined 3 channels from a 65k palette. If you careated a
16bit TGA texture with the same resolution, it would be 2.4MB in size.
mods and games for PCs, we often have the fortune of large amounts of
memory available, but creating art for low-spec machines, or even some
next-gen consoles, is a whole different matter. We need to be more
aware of how we use the memory available, and how we achieve the best
quality for our textures. Knowing more about how DXT compression works,
it can benefit you to use smaller-sized uncompressed textures, rather
than increasing the texture size to compensate for the DXT compression
and remaining within the same memory footprint.
you most likely have seen, if you use a heavily compressed JPG, the
texture becomes blurry, smeared and blocky. DXT has its similar blocky
problems, as it will affect up the image in what can be seen as an
uncontrolled way, something that can have devastating negative visual
impact on our textures. We need to be aware and verify our output when
saving out a normal black and white image as in Figure 1.1, where the
original from Photoshop looks white and crisp the result after saving
it as DDS could create something we see in Figure 1.2.
what happens with a small and simple texture like Figure 1.2, what
result can we expect from a larger, more complex in-game texture?
Let us start by looking at some areas where the DXT (and especially DXT1) format have problems:
Although not a true development example, this will still show how the
compression can distort the result of your textures and alphas. When
using heavily contrasted edges and lines within DXT, the variation in
anti-aliasing can create blocks around the edges of the object. As we
can see from Figure 1.3, there are two drawn circles. The left one has
been antialiased by Photoshop while the right one has manually been
adapted to retain its aliasing with a set of selective chosen
gradients. We can then seeFigure 1.4, which shows the output from DXT1.
To visualize the edge bleeding more clearly, we have intensified this
image's saturation and brightness.
As we can see, the difference between the two circles are very obvious
after the compression. The conclusion would be that using less
anti-aliasing to smooth out high contrast edges and using reduced
variation of colors can result in better remained visual sharpness in
Unique information in each channel:
Each 4x4 block within the texture shared by all channels can only
withhold 2 unique colors. When trying to use each separate channel for
unique information, the compression will distort the information of the
combined result, resulting in almost unuseable information. Therefore,
artists should refrain from using DXT in these occasions, due to its
limitations for this purpose.
Blocky texture content:
If we study textures that rely heavily on gradient content, we can
clearly start to notice the limitations of the 4x4 block compression
method. Let's look at a light map, where the information is vital to
define where the light is on the object, and how smooth the transition
Comparing Figure 1.5 and 1.6, where Figure 1.5 is the original
uncompressed data, we can clearly see that information gets distorted
with the compressed DXT1 compression in Figure 1.6. To achieve higher
quality, we can try various things:
- Use DXT3 or 5, with increased memory footprint.
- Increase the resolution of the textures, making each 4x4 block smaller.
- Limit the colors from the available palette in the original image.
- Choose an uncompressed format.
concept and solution is very simple - the cleaner we keep the texture
with the fewer variations, the better it's going to look. Let's take a
closer look at an example where we will experience banding and
pixelation, and see how we can improve on the final result.
16-bit Compression DXT1:
As mentioned earlier, DXT1 textures rely on 65k (16-bit) color
information. Creating textures that involve large gradient variation
will mean reduced quality and texture banding problems. Let's look at
the result from a compressed gradient palette.
figure 1.7 and 1.8, we can see that the 16.8 million color gradient
information from the original is fairly well-preserved in the
compressed 65k texture version.
But let's take a look at a more practical development example. Using assets from Battlefield 2: Special Forces BFHQ,
we will take a look at the visual quality when saved as DXT1 for
minimal memory usage. The image is used in a menu screen, and it
appears fairly up-close in an 800*600 resolution, so any large
differences will be visible.
1.9 shows the original TGA from Photoshop where we have a smooth
gradient of 256 colors in each channel. Comparing image 1.9 and 1.11 we
can see what type of information we have lost from the original image.
visualize the quality in further detail, let's zoom into part of the
affected area, as seen in Figure 1.10. Take notice of the area under
the foot, and the gradient fade on the right side from bottom to the
||Figure 1.9– Original Image
||Figure 1.10– Original Image Zoomed
saved the texture as DXT1 as seen in Figure 1.11, and zoomed in 1.12,
it has become obvious that we lost some valuable information, and this
is not the result we are looking for.
at the same area in Figure 1.12 as in Figure 1.10, with the DXT
compression the texture now appears crude. Banding has appeared within
the image under the foot in Figure 1.12, where the gradients blend
between the shadow and the ground.
Figure 1.11– DXT compressed image
Figure 1.12 - DXT compressed image, notice the banding under the foot.