He describes a hypothetical experiment to determine the spatial resolving power spatial resolution of your sense of touch.
Dithering with Symbol Patterns Reducing the number of colors or replacing specific colors is a very complex and difficult step in in Image Processing, and that is the topic covered in this example pages.
This includes determining the what colors to use color quantizationand how to place those colors on the image dithering, and patterning. This is so important that color reduction or quantization often happens automatically and behind the scene, just so ImageMagick can perform its original primary task of converting images from one file format to another, less colorful format, such as GIF, XPixmap, and XBitmap formats.
Knowing how this works can allow you greater control of the process, so as to improve the resulting image stored in a specific image file formats.
For example to convert a JPEG or PNG image containing millions of colors, into a GIF image containing a maximum of color, you really have to be able to reduce colors in a efficient and effective way.
Often during an image format conversion, this happens automatically behind the scenes, but there are other times when you want to do this manually. Reducing the number of colors in image is a typically a three step process, First you typically need to survey the colors an image uses.
Not only to see how many colors are actually used, but how often a particular color is used. It is no good preserving one specific color, if only a Two point threshold pixel is using that color, though sometimes you still need to do that.
Next you need to somehow decide on the final color set to which you want to limit your image. You may want IM to try and determine the 'best' set of colors for a specific image. Other times you may want something more general and global that can be used on any image.
You may even want to specifically add or remove a color from the set of colors that will be used. And finally you need to modify the image so as to only use the colors you have selected. Preferably you want it so the results will look good, or perhaps you want it so that it will compress, compare, or optimize well.
To further complicate matters, these steps are often interlinked, as one method of replacing colors, often can only be applied using specific sets of colors. And if you are using a specific set of colors, doing some sort of color survey is not needed, or perhaps you need to make exceptions for specific colors.
Basically while color reduction is often automatically handled behind the scenes, it is good to at least be aware just what it is happening, and what its effects will be.
Color Survey This is probably the lest important, and while IM provides you with methods to perform a survey, it is rarely done by users for the purposes of color reduction. I will leave further discussion to the relevant section, Extracting Image Colors.
There are four basic methods for the selection colors. These four color control methods: Here is an example of each of these four methods From this you can get an idea of what you can expect from each of them.
All the other methods have a fix set of colors according to the operators argument regardless of the image that is being color reduced. Only the first method " -colors " will actually pick colors based on the current image contents.
As the test image is predominately white, a lot of lighter colors is selected. It surveys the colors in an image using a technique known as "Adaptive Spatial Subdivision" using oct-trees. Then attempts to choose a specific set of colors to best match a specific image, within the limits given.
Two-point threshold definition is - the smallest separation at which two points applied simultaneously to the skin can be distinguished from one. The Threshold - Kindle edition by Anita Kovacevic. Download it once and read it on your Kindle device, PC, phones or tablets. Use features like bookmarks, note taking and highlighting while reading The Threshold. Jun 09, · Binaural Sleep Meditation Music for Positive Energy: Sleep Binaural Beats, Energy Sleep Meditation - Duration: NuMeditationMusic 2,, views.
See the Color Quantization Operator below. The color map " colortable. Using " -posterize " can also mathematically divide up each color channel into a set of color levels or intensities producing a 'uniform color map'. That is a color map with each channel set to a constant set of values or intensities.
This however only produces a minimal set of about about 8 colors. A very limited color set.
Threshold is also equivalent to a " -posterize " level '1' which picks 2 colors. Applying a Color Set Once you have a set of colors, the next problem is to apply the color to an image so that the existing colors are replaced by the selected set of colors.
This is known as 'Dithering', and is named as such because of its, "should I pick this, or should I pick that? Basically the idea of dithering is to place pixels of different colors near each other in such a way as to fool the eye into seeing more colors in the image than is actually used.
That is the color in that area of the image more closely matches the original color of the image, because of the way the human eye 'merges' neighbouring colors together. One of the best introductions to Dithering is on Wikipedia though you will need to skip over the 'Audio Dithering' section at the start.
This presents an excellent set of examples of the benefits of using a dithered pattern of pixels, when you have a limited set of colors. The basic styles of color replacement include Direct Color Mapping threshold, and posterization Random Dither purely random placement of pixels Error Correction Dithers pseudo-randomized patterns of pixels Ordered Diffused Pixel Dither regular patterns of pixels Digital Halftoning dots of different sizes Direct mapping if the nearest color in a given set is what was shown above.Color Reduction Introduction Color reduction is a very important aspect of ImageMagick.
For example to convert a JPEG or PNG image containing millions of colors, into a GIF image containing a maximum of color, you really have to be able to reduce colors in a efficient and effective way. This is an interesting experiment, but there is a useful side to the information. This psychological phenomenon is known as the two-point threshold, and it can be used to test for nerve damage.
Also, Braille dots were designed so that they were farther apart than the two-point threshold. Once the participant has perceived two points on two consecutive trials feel free to skip that testing area, and use the 1 st two-point increment as the threshold value.
For example, if on the back of the hand the participant feels two points at 10mm and 15mm, use 10mm as the threshold. the point of stimulant division, which is, the shortest distance between two spots of arousal on the skin at which the two stimulants are interpreted as two stimulants instead of as a sole stimulant.
TWO-POINT THRESHOLD: "The two-point threshold is commonly referred to at the spatial threshold.". The Threshold - Kindle edition by Anita Kovacevic. Download it once and read it on your Kindle device, PC, phones or tablets.
Use features like bookmarks, note taking and highlighting while reading The Threshold. 2. Minimum or maximum value (established for an attribute, characteristic, or parameter) which serves as a benchmark for comparison or guidance and any breach of which may call for a complete review of the situation or the redesign of a system.