Many are not interested in the speed of the scanner as such, but in the possible methods of increasing this speed. Sometimes they even ask about the ways of hardware "overclocking" of scanners. Adherents of the latter will be forced to immediately disappoint: overclocking of the scanner is impossible, even purely theoretically , as well as "acceleration" of, say, an oscilloscope . Inside the scanner, you will not find any items (switch, jumper, additional connector) designed for such an operation ... Why? Because most of the electronic cascades of your instrument are very sensitive to changes in the clock frequency, and if this frequency is increased by more than 1 ... 2% - the scanner simply stops working.

"This problem is not solved in the forehead". Therefore, it is proposed to reformulate the problem, and instead of "speeding up" we talk about "saving time in scanning". As practice shows, there are three main ways to reduce the time of image digitization:

1. Correctly configure the computer used for this job;

2. Learn how to optimally choose the scanning parameters for a particular original;

3. Do not use outdated versions of the scanner driver.

On the question of the optimal computer configuration, there is no ready answer: the speed of the "computer + scanner" system in the general case depends on a variety of heterogeneous and mutually dependent parameters. Below, an attempt will be made to identify the most significant of them. Why is this necessary? This article is intended primarily for a person who is tormented by the question "What would you like to twist in order for it to run?", Perhaps even frustrated by the lack of a pen with the inscription "Speed", which could be turned to the limit ... Therefore, the purpose of the article is In understanding what, where and how it makes sense to tune.

The choice of scanning parameters is quite common, many materials are devoted to this issue, both on the Web and in computer periodicals, so we will not dwell on it here. It is enough to give a universal advice: do not get carried away with permission ... more - does not mean better. Information on the optimal choice of scanning parameters can be found at http://www.mustek.ru/ , http://www.scaner.ru/ and http://www.ixbt.com/ (in the "Periphery" section).

The choice of the driver version among the main methods is not accidental: there are many cases when a fully functioning device on a correctly configured computer worked slowly and unstably only because it was controlled by the driver of the "day before yesterday" version. Information on the current versions of drivers you can always get on the websites http://www.mustek.ru/ and http://www.scaner.ru/ , or in the Moscow service center Mustek: by phone (095) 962-10- 42, 737-80-63; By e-mail: [email protected] .

An important question is the choice of operating system. The fact is that the manufacturers of SOHO class scanners are oriented to the mass consumer, which according to statistics rather prefers Windows 3x / 95/98 than DOS, Windows NT and * nix-clones. Naturally, the drivers are first written for Windows 3x / 95/98, and only then are versions released that are converted to work under other operating systems. So do not be surprised if your device is unstable running under an exotic operating system - this should be expected. Under what system it is better to work with the scanner, I think you have already understood ...

Now back to the most difficult question: the optimal configuration of the computer. To be able to evaluate the contribution of each of the devices participating in signal processing and to select those parameters whose influence is large, you will need to consider the entire scanning process - from initializing the scanner to displaying the finished image. It would be very difficult to cite a generalized scanning algorithm, but several main stages of this process can be identified. When digitizing any image using any flatbed scanner, the following procedures are mandatory (in one or another sequence):

1. Calibration (auto-tuning of converter stages);

2. Moving and positioning the carriage ("reading head");

3. Interrogation of the elements of the photosensitive matrix (CCD or CIS) and analog-to-digital conversion;

4. Accumulation of the received values ​​in the memory ("buffer") of the scanner;

5. Initialization of interface devices and transfer of accumulated information to the computer's RAM;

6. Record ("save") information on the hard drive (hard disk);

7. The transfer of control to the driver that caused the driver (sometimes this is followed by opening the resulting image in a separate window).

Note: sometimes "warming up" is performed before scanning, but this procedure is not mandatory for all scanners and can often be turned off, so it is not considered here.

Obviously, procedures 1 ... 3 of external correction are not amenable, since they are always performed by the scanner automatically and do not depend on any parameters of the working computer.

The calibration procedure is performed using a rigidly defined algorithm, which is determined by the set of instructions stored in the internal firmware. Change the algorithm is possible only together with ROM (which does not always look like a separate chip), so talking about optimizing the time costs for this procedure is meaningless.

Moving the carriage of the flatbed scanner is done by a pull mechanism, driven by a step motor. In general, the carriage speed depends solely on the selected scan resolution (see above for the resolution choice). The mechanism, of course, introduces some own delay (the time of the signal passing through the chain "the scanner processor - the buffer cascade - the motor controller" plus the time of the step), but it can not be compensated by external means.

External interference in the circuits that realize the opto-electronic, and then the analog-to-digital conversion, can be realized only at the level of substantial processing of the corresponding electronic cascades, and is therefore not considered here either.

Interim storage of data in the scanner's RAM (procedure 4), as well as the amount of this memory itself, remains a subject of lively discussion for a long time: will it be faster if the memory is added? The discussion, unfortunately, is pointless: connectors for additional microcircuits (or modules) of RAM for the scanners manufactured by Mustek, Plustek, Avision, Genius, and Targa are missing, even with such a powerful device as Mustek Paragon Power Pro.

If we talk about flatbed scanners of other manufacturers, then there are professional models (price category "above $ 5000"), in which there are such connectors, but I do not have data allowing to estimate the effect of buffer size on the performance of these models.

The bandwidth of the interface devices is considered to be the bottleneck of the scanning process. This is not entirely true: the time spent on preparing and transmitting information (procedure 5) becomes noticeable only with large volumes of the image.

Indirect evidence can serve as experimental data presented in the tables (for color , halftone and black-and-white modes): scanners with a "slow" EPP interface noticeably inferior to "fast" scanners with a SCSI interface only when the volume of the image obtained exceeds 25-30 MB. Obviously, for most problems solved with SOHO class scanners, smaller file sizes are characteristic. For example: text recognition: resolution 300 dpi, original size 210h290 mm, image size - about 8.5 MB; Scanning photos format 10x15: 300 dpi, the image size - about 6.2 MB. Therefore, if you do not handle more demanding tasks (such as batch scanning from negatives), the selected scan resolution will affect the performance of your scanner much more than the configuration of the interface devices.

Nevertheless, there are a number of conditions that can somewhat speed up the operation of the interface devices of your scanner.

• If your machine is connected to a parallel port on your computer, you should pay attention to the mode in which the port controller works. Traditionally, it is recommended to install EPP \ ECP, however most modern BIOS supports various variants of this mode: EPP v.1.7, EPP \ ESP v.1.9, and so on. In the general case, it is possible to determine the optimal variant only experimentally. For reference, the scanning time of A4-size sheet with Mustek Paragon 800 II EP (400 dpi, color mode) is given below. The data was received on a test computer .

  Mode	SPP	EPP	EPP use DMA 1		EPP use DMA 3		ECP use DMA 1		ECP use DMA 3
  Time, seconds.	588	234	260		528		495		488

  Most SCSI scanners of the SOHO class are now equipped with DTC3181-type controllers or similar. These controllers do not have their own BIOS, the only control available to users is jumpers J1, J2, which specify the support for Plug'n'Play and the value of wait state (WS), respectively; The second parameter defaults to "1". It is a common misconception that setting WS = 0 results in "speeding up" the scan. Unfortunately, this is not true: at best, the scanning speed will not change, at worst you will receive a message like "Scanner not ready" ...

There are cases when a significant slowdown of the scanner resulted in a conflict between two SCSI controllers. If this problem can not be solved by reassigning resources to conflicting devices, consider installing the scanner as part of the SCSI chain to a more powerful controller. In this case, the scanner must be the last device in the chain, it should be terminated, and the SCSI ID should be set to the position corresponding to the requirements of the controller used (permissible positions: 1 ... 6). The existing experience of using Mustek scanners with high-speed controllers Adaptec 2940 AU and Asus SC-200 PCI shows that the scanner connected in this way works faster than with the "native" SCSI-II DTC3181 card.

• Flatbed scanners with ISA and USB interfaces are currently on the market a bit - due to the "antiquity" of the first and the novelty of the second interface. In a sense, they are united by the fact that the hardware and software of both ISA and USB do not provide any intervention by the user.

Procedure 6 (recording of the resulting image to a disk file) is performed by the disk subsystem of the computer - without the participation of the scanner. If the hard drive of your computer is released less than ten years ago, then it will not be necessary to optimize its performance - provided that the size of the received files rarely exceeds 10 ... 15 MB.

With larger volumes of processed information, the influence of the disk subsystem on the total scan time increases, then it makes sense to evaluate, perhaps - to improve the performance of the hard drive in use. Specific ways to "accelerate" the disk subsystem are not considered here, you can find out more about this on the wonderful site iXBT, in the "Media of Information" section .

Return control, opening the image in a separate window (procedure 7), as well as downloading the scanner driver, occur the faster, the larger the amount of RAM and the more powerful the video subsystem of the computer. On the test computer, the above- mentioned processes had a negligible duration (an average of about 0.2 ... 0.5, 1.0 ... 3.0, and 0.5 ... 1.5 seconds, respectively).

Issues related to the speed of the video subsystem are also covered in detail on iXBT, in the "Video System" section.

Thus, there are only two "points of application of forces" for those wishing to optimize the process of scanning at the hardware level: interface devices and possibly a disk subsystem . There are, of course, other, more exotic options (for example, replacing the motherboard and / or CPU of the computer ), However, such operations for all the desire to "configure" the computer can not be counted.

In conclusion, I would like to give a brief reference. Accepting the number of successful attempts of the "scanner acceleration" known to the author for 100%, we obtain the following frequency ratio of the methods used:

1. Configuration of the working computer ............................................... ............10%

2. Optimal selection of scanning parameters ........................................... 50%

3. Updating the scanner driver version or switching to another OS ................. 35%
4. Combination of methods 1 ... 3 ........................................... .....................................5%
   
   Date: 19.01.2004