Misunderstanding in scanner reports

Scanners have become one of the hottest products for computer peripherals. This is an indisputable fact. Therefore, whether it is professional media, mass media or various magazines, networks, scanner manufacturers, agents, etc., are promoting and reporting scanners. This has contributed to the popularity of scanners and improved people's awareness of scanners. With the development of the network and the popularity of computers, the demand for scanners will increase substantially, and scanners will continue to be the focus of media coverage.

As a loyal reader of the scanner's report, it does benefit from these articles. However, there are a few reports that in my opinion there are defects or intentional confusion, or the concept is unclear. I have summarized some of the errors in the scanner reports for your reference.

Misunderstanding: Misunderstanding about Scanner Resolution

The resolution of the scanner is divided into optical resolution and maximum resolution. Optical resolution is an important indicator of the scanner. The higher the optical resolution, the better the scanner's performance. Optical resolution is divided into horizontal resolution and vertical resolution. The horizontal resolution is related to the optical system, the true resolution of the CCD, and the hardware design circuit. The vertical resolution is based on how many steps per inch of the stepped TV in the mechanical design of the scanner can be moved. It is related to the stepper motor and the mechanical transmission part, so the vertical resolution is not as important as the horizontal resolution. The optical resolution mainly refers to the horizontal resolution. The most popular 600dpi and 1200dpi currently on the market refer to horizontal resolution.

The correct representation of optical resolution should be: horizontal resolution × vertical resolution. For example, for a scanner with a horizontal resolution of 600 dpi and a vertical resolution of 1200 dpi, the correct representation should be 600 dpi x 1200 dpi. However, in some articles, publicity materials or some online introduction of optical resolution, the vertical resolution is written in front, and the horizontal resolution is written in the back, for example, 60 Odpi×300 dpi or 1200 dpi×600 dpi. In the past few years, only a few companies were found to have written this way. In the past year or two, there have been a number of companies or media outlets that advertised. Instead of correcting such mistakes, there is a tendency to expand publicity. When the scanner has not reached the level known to everyone, some media, especially a number of manufacturers, have also publicized this, whether they knowingly commit suspicious circumstances or have obvious misleading effects.

There are also individual brands that only write the maximum resolution when introducing the resolution. Such as 2400dpi, 4800dpi, 9600dpi and so on. This makes people wonder what its optical resolution is. We know that the maximum resolution is calculated using optical resolution and then calculated by software interpolation. It is also called interpolation resolution. The maximum resolution of the scanner is usually 2 to 4 times higher than the optical resolution. At maximum resolution, the scanner cannot capture other "real" data. It generates new pixels between the pixels that the optical system can sample and does not really add detail to the image. Therefore, it is not appropriate to introduce only the maximum resolution.

Misunderstanding #2: Misunderstandings about Scanner Colors

The number of color bits in the scanner is also called color depth, which expresses the ability to capture the color of the image. Theoretically, the 24-bit scanner can distinguish between 256 shades of gray and 16.77 million colors; the 36-bit scanner can distinguish between 4096 shades of gray and 68.7 billion colors; the 42-bit scanner can distinguish between 16384 shades of gray and 4 million colors; The 48-bit scanner can distinguish between 65536 shades of gray and 281 trillion colors. With the development of scanner technology, many scanner manufacturers use "bit enhancement technology" to increase the number of color bits in the scanner. However, in media reports or promotional materials, some brands do not specifically indicate that only the number of color bits in a scanner is reported as 42 bits, 48 ​​bits, etc., without actually mentioning the number of colors, may actually be only 36 bits or less.

The so-called true color number is the number of bits that the scanner hardware can achieve. The number of digits of the scanner is determined by the number of digits of the analog/digital (A/D) converter inside the scanner. For example, a 36-bit color scanner should use three 12-bit A/D converters. For higher-level color scanners such as 42-bit scanners, three 14-bit A/D converters should be used. If three 12-bit A/D converters are used, the other two are implemented by software. Bit enhancement technology. There is a difference between the number of bits obtained through software enhancement and the number of bits scanned by the hardware, which directly affects the ability of the scanner to capture colors. Some vendors have written very general information, confusing the number of true color bits with the number of bits obtained using bit-enhancement techniques, leaving readers with some trepidation. The correct approach should first indicate the true color number.

Misunderstanding 3: The dynamic range of the scanner

When the relevant media evaluates the performance of the scanner, I have repeatedly found that when reporting the dynamic range, the dynamic range value is written as a hundred-digit value, such as dynamic range = 241, 250, and so on. This type of writing is wrong. It mainly confuses the concepts of the dynamic range value and the gray level that can be expressed.

The dynamic range, also known as the density range or concentration value, is the range of tones that the scanner can record, usually referring to the range from near pure white to pure black.

In the scanned image, the density is used to measure the original color separation film and print. In theory, the degree of lightness in a part of a reflection or transmission document is related to reflected light (reflection) or transmitted light (transmission). If the reflectance R is used to represent the degree of darkness of the reflected image, the R value is between 0 (full absorption) and 1 (total reflection). Similarly, if the transmissivity T is used to indicate the lightness and darkness of the transmissive sheet. The value of T is between 0 (full absorption) and 1 (full transmission) because the degree of lightness and darkness of the human visual perception is not linear with the reflectivity of the reflective sheet or the transmittance of the transmissive document, but is the reflectivity or The transmittance is approximately linear with a logarithm to base 10. Therefore, the reflection density Dr=lg1/R and the transmission density Dt=lg1/T.

In fact, the dynamic range of the scanner is directly related to the number of digits of the scanner. The dynamic range of the scanner is represented by a base 10 logarithm that the scanner can distinguish the light and shade levels. For example, the 24-bit scanner can express 256 gray levels, so the maximum dynamic range is D = lg256 = 2.4, but the 24-bit scanner may not fully display 256 levels, and the general dynamic range is 2.2, ie the scanner The gray level that can be expressed is 10 to the power of 2.2, which is 159. Also see Table 1 for the dynamic range of the 30-bit, 36-bit, and 48-bit scanners.

Therefore, when introducing the measured dynamic range of the scanner, if the measured gray level is 241, the dynamic range should be written as:

D=lg241=2.38 instead of 241.

Misunderstanding #4: Myths about scanning speed

Scan speed is an important indicator of the scanner, but there is a certain contradiction between scanning speed and image quality. Under normal circumstances, people always want the scanner to be fast, but it should be that the scanner works through the light source of the scanner and uses a color separation method and a charge coupled device (CCD) array to collect the optical information of the scanned object. It takes a certain amount of time to get the image information and transfer this information to a computer image file. The speed of the scanner is good, but it does not affect the image quality. Therefore, it is not the scanner that scans as fast as possible. A very high-speed scanner may lose some scanned image information during the scanning process. Some scanners scan fast at low resolutions, but scanning speeds at high resolutions are not necessarily fast. At the same time, the speed of the scanner has a close relationship with the system configuration, scanning resolution setting, scan size, etc., and cannot generally report the speed of the scanner.

At present, many scanners use the most popular USB interface at a transmission rate of 12MB/S. A few scanners use the IEEE 1394 (FireWire) interface. Their common feature is plug and play, hot swappable, and fast, especially the IEEE 1394 interface is faster.

The IEEE 1394 standard has two bus modes, the BackPlane mode and the Cable mode. Backplane mode supports transmission rates of 12.5MB/s and 25.5MB/s, while Cable mode supports transmission rates of 100MB/s, 200MB/s, and 400MB/s. And is developing 3.2GB/s transmission rate products.

I have noticed that a number of media and manufacturers have reported that the speed of the IEEE 1394 scanner is 33 times faster than that of the USB scanner. If the IEEE 1394 interface is used, the 400 Mbps transmission rate of the Cable mode is comparable to that of the USB 1.0 version. ,this is correct. Usually IEEE 1394 is faster than USB, which is also an indisputable fact. But also depends on which mode IEEE 1394 is used. At the same time, the USB2.0 scanner has been introduced, and its transmission rate can reach 480MB/s. It is believed that USB2.0 scanners will soon be available on the market.