# Three-dimensional terminology

- Jun 05, 2019-

1. Pitch :Concave-cylinder grating refers to the chord length of an arc. Grating pitch is the width of grating grid line. There are many ways of the grating pitch unit, e.g. grating width (mm) as a nominal (commonly found in domestic grating sheet), but also grating density (lpi) as a nominal (commonly found in imported raster). Another, to use the point of photo printing machine or printer (pixel) as a nominal.

Conversion relationship of the three units: (1lpi) = 25.4 / (1 mm) (1pixel) = printer resolution (dpi) / (1lpi)

When grating was processed in the factory, due to the physical processes” hot press, cold condensate”, the actual nominal value of grating pitch has s certain deviation with the nominal value when leaving the factory. Second, many types of inke-jet printers and offset printers can not achieve its desired accuracy, which will inevitably lead to that the output raster images and raster imaging sheet don't match (particularly when doing large-scale pictures). Thus, we use a specific output device (ink-jet printer or offset printer) to test a particular grating, and use the number of printed dots (print marks) pixel to express. In this way, regardless of the nominal value error when leaving factory and output device error, we can ensure that output images of the raster image fit for the grating sheet well.

2. Line numbers : the number of lines per inch. 1 inch = 2.54 centimeters.

Number of lines = one inch / pitch = 2.54/XX

3. Pixels: the number of points per unit pixel (the image resolution), that is pixels / inch or pixels / cm.

4. Raster : grating means that it can be attached to the outside screen, and we see a vivid three-dimensional portrait by the different viewing angles and two principles of light refraction, and it is a kind of material by printing and pressing technology.

5. Viewing angle: it refers to the maximal effective angle which our eyes through the grating material can see clearly the 3D picture screen.

6. Viewing change angle: it means that eyes through grating material watch 3D picture screen and the angle which eyes need move from one screen to the other one.

7. Resolution: Resolution refers to the number of points (pixels) per unit. When making an image, the resolution which is set in PHOTOSHOP, that is resolution of the images, unit: pixels / cm, or pixels / inch.

There are strict requirements of resolutions for 3D picture, mainly about several points:

1) Pitch and the lines: They have a close relationship. Pitch determines the number of lines ( the number of lines is the number of pitches per inch).

2) Layers: When making a picture, the number of images, you can also refer to the number of layers in PHOTOSHOP, but the former is more precise.

3) Focus thickness(i.e. medium thickness): The medium thickness which Grating focus needs.

4) Printing orientation: It refers to the moving orientation of printing car when printing, when the car's direction of movement and the direction of texture are parallel, we call it horizontal, when intersecting, we call it vertical.

5) Viewing distance：It refers to the distance we are away from the picture when we watch the picture. Different grating materials have different viewing distances