On three kinds of "imitation color" patterns in GIF indexed color images

Index so-called " Imitation Color "Can be understood as the imitation of color, mainly used in the want to use less color to express the rich color transition occasions, like to use very few raw materials to make a sumptuous dishes generally.

We can feel it. Create a new 300x100 pixel RGB mode image in Photoshop, select the Gradient tool 〖g/shift G〗, select "Blue, Red, yellow" in the default gradient list, and fill the gradient definition line from left to right with the full image to form the effect of the following figure.

Then select the menu "image > Mode > Index Colors" will appear in the Settings box, the parameters of which are set according to the following figure.

We will see that the image shows the effect of the following figure. This is because we now specify that only 8 colors can be used to express this image. In the absence of the imitation color of the image from the original smooth transition into an adjacent color block, the number is exactly 8. This is the closest color Photoshop can draw to the original image. Obviously, this is not enough to express the original image.

So, is it necessary to use more color to produce a better transition effect? Not necessarily, we can select different color-copying options in the Settings box, and you will see the following effect. It was obvious that the color transition had softened. Note the number of colors in the settings box is still 8, which means that the number of colors does not change.

So why does the color transition look a lot smoother? The mystery is in the image below, this is the diffusion of imitation color of the local amplification, we see a variety of colors are no longer mutually independent of the color block, but each other for the integration of infiltration, so that the overall visual effect of the human eye will form a smooth transition.



Diffusion Imitation color amplification diagram

The most commonly used in three kinds of color-imitating methods are diffusion, because it works best and can adjust the degree of imitation (that is, the number, the value is a percentage). The second is the pattern, the two color infiltration are more orderly and regular. And the noise pattern is irregular, it looks more cluttered, so it is less used.

Imitation color is more commonly used in web design, because reducing the number of colors can reduce the number of bytes in the picture, which is conducive to fast delivery on a network with limited bandwidth. Of course, too little color is bound to lose the quality and detail of the image, so the tradeoff between image quality and image byte number is a problem that is often encountered when making Web pages. Some novice pursuit of high image quality, resulting in the entire Web page image byte number of large, slow transmission. or excessive pursuit of transmission speed, significantly reduce image quality. Both extremes are undesirable. And skilled producers must be the ability to achieve the best balance between the two. The Web pages produced by these people are not only high in image quality, but also faster in transmission.

In this case, the best balance between the two is not just how to optimize the image (that is, to minimize the number of bytes at the same time as possible to ensure quality), but also in the design process to be prepared for future optimization. For example, do not use a large area of transition color.