Basic scanning concept

Scanners are instruments used to convert photos, slides or hand-drawn originals into digital data.

It is divided into two categories: platform scanners and cylinder scanners. The platform of the platform scanner is flat and compact. The CCD (charge-coupled device) is used as the photosensitive element. The cylinder of the cylinder-printing machine is complex and has a complex structure. PMT (photomultiplier tube) as a photosensitive element.

With the development of CDD technology, there are platform scanning machines in the market ranging from low-cost monochrome scanners to high-priced professional color scanners. Professional platform scanners are generally cheaper than conventional drum scanners, but they are scanning. Can get similar quality.

2. Digital Input

A method of representing input information using a binary number or bit.

Modern digital input allows the image to be processed and repaired with precise computer control, with great flexibility, and the final result can be easily duplicated without any loss of quality. Compared to photography or hand-painted manuscripts, digital files stored on disk or other media ensure the authenticity and integrity of the data.

3. Original (Original)

The original form of the image, such as photos, slides, or books and magazines. Compare the definition of images and replicas.

According to the different reactions of the original to light, it can be divided into two categories: reflective draft and transmissive draft. The reflective draft is an original printed on an opaque coating. It absorbs some components of white light and reflects other components, such as photos, Printed matter, magazines, etc. are reflective drafts; transmitted texts are originals printed on photosensitive transparent substrates. They absorb certain components of white light and transmit other components such as 135mm negatives and 4x5” positives. The color of the transmitted manuscript is the response of the human eye to those reflected or transmitted light combinations.

4. Image

The resulting rasterization results from scanning an original. Compare the definition of originals and replicas.

5. Copy (Copy)

Several prints of a single image. Compare the definition of originals and images.

6. Pixel

Digital images consist of lattices. The points that make up an image are called image elements, or pixels.

The pixel is the smallest unit of the bitmap image and is a square dot. The scanner passes through the sample manuscript and stores each sample as a pixel so that the pixels produce a dot matrix. The higher the resolution of the scanner, the smaller the pixel. The scanner resolution unit is the number of sample pixels per inch (pixel per inch), and dpi (dot per inch) is the number of dots that can be copied in each inch, applied to the output machine.

7. Sample Depth

It is used to calculate the number of gray levels or colors that can be contained within the bitmap image, also called bit depth.

The pixel depth is in binary units. If the pixel depth is 1, the image can only contain two gray levels or colors (for example, black-and-white images). When the pixel depth is 8, 256 gray levels or colors are allowed. The pixel depth is 24 hours allowed 16 million colors (224).

The device in the RGB input mode has a smaller range than the visible light color space. The pixel describes the color that most closely matches the original in the RGB color space. The larger the color space, the more accurately the original image is described. Color space range units are defined as pixel depths in digital images.

8. Red, Green, Blue (RGB)

The three primary colors of light. This three colors can be used to synthesize most of the colors visible to the human eye.

9. Cyan, Magenta, Yellow and Black (CMYK)

Cyan, magenta, yellow, and black are the basic colors used in printing, in which cyan, magenta, and yellow are subtractive primary colors, and other colors can be synthesized; black is used to replace cyan, magenta, and yellow colors with equal color values. Plays a role in saving ink and enhancing tone performance and increasing color reproduction range.

10. Charge coupled device (CCD)

A charge coupled device is a full-microelectronic photo-sensing device that is used as a photosensitive element in a stage scanner to convert the amount of light into an electronic signal.

11. Resolution

Used to measure the spatial detail accuracy that a device can record or generate. The higher the resolution, the finer the details. The unit of resolution is the number of elements per unit length. For example: pixels per inch is the unit of resolution for the microscope scanner and screen, and the laser element per inch is the resolution unit for the printer and laser imagesetter.

12. Optical Resolution

The resolution of the scanner's hardware (CCD) on the original.

13. Interpolation Resolution

When the required resolution is higher than the scanner's optical resolution, interpolation software is required to increase its resolution, but in fact the result of excessive interpolation is blurring and distortion, as well as a waste of hard disk space.

14. Input resolution

The number of pixels per inch that the scanner can capture when scanning an original. In pixels per inch (ppi).

15. Print output resolution lpi (Line per inch) (Output)

The number of lines per inch, the unit used to measure the frequency (interval) of the screen in a halftone screen, usually in the range of 55 to 200. The higher the frequency, the smaller the halftone dots and the higher the quality of the printed image.

16. Continuous Tone

Continuously changing color image.

When no halftone dots are included, the original is a continuous tone image, and the transition from color to color is continuously invisible. The photo is a continuous original.

17. Half Tone

A technique for copying a continuous-tone manuscript, such as a photograph, which divides the image into many points, reflecting the depth of the color by the different sizes of dots.

The printer prints a matrix of tiny dots of different sizes with a limited number of sets of inks (only black ink or cyan, magenta, yellow, black ink), which can give the human eye an illusion of many shades of gray or many colors.

18. Density

The darkness of the image on paper or film.

For paper, the less light reflected by the reflective material, the higher the density; for the film, the less light transmitted by the transparent material, the higher the density value, the paper density range is about 0.0D to 2.0D, the density range of the film About 0.2D to 4D.

19. Maximum Density

The highest density level in the original or image, no image information above this density level can be found in the image or original.

20. Min. Density

The lowest density level in the original or image, no image information below this density level can be found in the image or original.

21. Density Range

The density difference between the minimum and maximum density of an image.

22. High Light

The brighter area of ​​the original or image.

23. Shadow

The darker area of ​​the original or image.

24. Descreen

Techniques to remove halftone textures by soft focus when scanning prints to avoid collision.

25. Color Shift

The inaccurate color caused by the overall bias of a manuscript, image or reproduction to a certain tone is called color shift, and color shift may prevent high-quality reproduction.

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