Positive CTP plates and negative CTP plates are two different types of printing plates used in the computer-to-print process. The main difference between them is the way the image is presented and processed. The following are the differences between them:

1. Positive CTP plate:

- A positive CTP plate is a type of printing plate used to output images in the forward direction. During the plate making process, a laser light source is directed onto the plate, making the laser-irradiated areas hydrophilic and the non-irradiated areas hydrophobic.

- During the printing process, ink does not adhere to the laser-irradiated areas, but to the non-irradiated areas, resulting in the formation of an image.

- Positive CTP plates are suitable for most graphic printing, such as books, magazines, leaflets, etc.

2. Negative CTP plate:

- Negative CTP plate is a kind of printing plate used for negative output image. In the process of plate making, the plate is directly irradiated by a laser light source, which makes the laser-irradiated area hydrophobic and the non-irradiated area hydrophilic.

- During the printing process, the ink adheres to the laser-irradiated areas but not to the non-irradiated areas, resulting in the formation of an image.

- Negative CTP plates are suitable for certain special printing needs, such as package printing and bill printing.

Although positive CTP plates and negative CTP plates differ in the way the image is presented and processed, they also have some things in common. The following are some of the similarities between positive CTP plates and negative CTP plates:

1. Plate-making technology: Both positive CTP plates and negative CTP plates adopt computer-to-print (CTP) plate-making technology, i.e., the image transfer and plate-making process is realized by directly irradiating the plate with a laser light source.

2. High precision: Both positive CTP plate and negative CTP plate have high precision plate making ability, which can precisely transfer the image to the printing plate and ensure the quality and accuracy of the printed materials.

3. Cost saving: CTP technology can directly transfer digital images to the printing plate, eliminating the traditional plate-making process, reducing labor and time costs, and improving printing efficiency.

4. Environmental protection: both positive CTP plate and negative CTP plate adopt the technology of chemical-free plate making, which reduces the pollution to the environment and meets the modern environmental protection requirements.

5. Scope of application: Both positive CTP plate and negative CTP plate can be widely used in graphic printing, packaging printing, label printing and other fields to meet different printing needs.

To summarize, although the positive CTP plate and negative CTP plate are different in the way of image presentation and processing, they have some common features in terms of plate making technology, high precision, cost saving, environmental protection and application scope, etc. They are commonly used plate making materials in the modern printing industry and play an important role. According to the specific printing requirements and effects, it is very important to choose the right CTP plate material.