Article: The Use of Downsampling in Illustration Techniques

Which Illustration Technique Uses Downsampling?

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Downsampling is a process of reducing the sampling rate or sample size (bits per sample) of an audio signal to reduce file size and data complexity. It can also be used to enhance audio quality by removing artifacts such as aliasing.

Anti-Aliasing

Anti-aliasing is an image processing technique that smooths jagged edges to make the images appear sharper and more realistic. It is used in both vector and raster graphics.

There are a few different types of anti-aliasing, but most of them work by downsampling or supersampling the pixels and then using various techniques to blur the edges of the shapes. This reduces the jarring, step-like appearance of aliased curves and diagonal lines.

Anti-aliasing is a very computationally intensive process so it can be quite slow to render games with AA enabled. The amount of time it takes to perform the anti-aliasing will depend on the screen resolution and severity of the aliasing. You can adjust the level of AA by selecting the appropriate option in the Options menu. This will increase or decrease the amount of downsampling and computational complexity. The higher the AA setting, the better the image quality will be but it will take longer to render each frame.

Texture

Texture is an artistic technique that aims to immerse and engage the viewer into the artwork through bumps, ridges, grooves and other physical characteristics. It’s used in painting and sculpture to create depth and add interest.

During downsampling, the template pattern values (e.g., 0 through 8) are accumulated to create a table. The four bits (?) that occur most often for each of the template patterns are stored to be used during upsampling.

The accumulated table is accessed by processing logic that sums the pixel data values for each block of downsampled pixels and selects the template pattern value to use during upsampling. There are a number of tie breaker systems that may be employed to decide which of the many possible pattern values to select during upsampling. Exemplary tie breakers include using the most common pixel value in the original size (e.g., if the most common pixel value is white, then white is used during upsampling). Other tie breaker systems are also apparent to those of skill in the art.

Contrast

Contrast is a design principle that relies on opposites to grab the attention of the viewer and convey your message. It’s as simple as using light against dark to make the subject stand out, or contrasting colors and sizes to show relationships between elements. There are many ways to use contrast, and it’s important to understand how it works to create compelling compositions that tell your story.

When the template is downsampled, the statistical information for patterns of upsampled pixels is maintained and is later used to perform elastic interpolation. This avoids blocking effects by ensuring that the sampling rate vector evolves in all blocks evenly, not just at the borders of each block.

When the image is split into blocks, the sample rate vector is computed based on a Perceptual Relevance (PR) metric. This is later translated into a list of value pairs for all corners of each block. These values are then used during elastic downsampling to avoid blocking artifacts.

Color

The color component of an image is often downsampled (one value per 2×2 block of pixels) to reduce size, but the resulting images are not as high quality as one would hope for. A technique known as error diffusion provides a way to improve the quality.

Error diffusion works by allowing four upsampled pixels (two horizontal and two vertical) to be represented by a single sampled pixel. This is accomplished by sampling the pixel value at least twice as many times as there are pixels, and redistributing the sampled values to the four upsampled samples (processing block 504).

Statistics are accumulated for each template pattern value in the downsampled image, and a table is stored with the corresponding four bit binary pixel patterns. This information is signaled to the upsampling unit along with the downsampled image, or separately. If a pattern occurs more than another, a tie breaker system is used to decide which one to use during upsampling.

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