Interfaces for film scanners

How is a film scanner connected to a computer? As known, computers offer a lot of different interfaces that mainly differ on the data transmission time and the length of the cable. As in case of a scan of a high resolution, the modern film scanners partly have to transmit several hundred megabytes to the computer, a high data transfer volume of the interface is needed in order not to unnecessarily enlarge the scanning times.

The obsolete serial and parallel interfaces are long ago not sufficient anymore for slide scanners. This is why only USB, Firewire and SCSI can be considered, whereby there are increasingly less models with a SCSI-connection, as for SCSI, a separated SCSI-controller is needed that has to be specially installed into the computer and that is not really cheap. This is why most of the modern slide scanners are delivered either with an USB- or a Firewire-interface.

Interface Max. transmission speed Max. cable length
USB 1.0/1.1 Full-Speed 0,2 MByte/s 5 m
USB 2.0 Highspeed 60 MByte/s 5 m
USB 3.0 Superspeed 625 MByte/s 5 m
Firewire IEEE 1394a 50 MByte/s 4,5 m
Firewire IEEE 1394b 100 MByte/s 100 m
Firewire IEEE 1394-2008 400 MByte/s 100m
Serial interface 0,12 MByte/s 100 m
Parallel interface 2 MByte/s 5 m
SCSI (SCSI-1) 5 MByte/s 6 m
Fast SCSI (SCSI-2) 10 MByte/s 3 m
Ultra SCSI 20 MByte/s 1,5 m
Ultra Wide SCSI (SCSI-3) 40 MByte/s 1,5 m
Ultra2 Wide SCSI 80 MByte/s 12 m
Ultra-160 SCSI 160 MByte/s 12 m
Ultra-320 SCSI 320 MByte/s 12 m
Serial ATA 1,5 GBit/s 150 MByte/s 2 m
Serial ATA 3,0 GBit/s 300 MByte/s 2 m
Serial ATA 6,0 GBit/s 600 MByte/s 2 m

In the table above, the maximum transmission speed and the maximum cable length for numerous interfaces and variants of interfaces are compared. One recognizes immediately that the obsolete serial and parallel interfaces cannot be considered anymore for the tramsmission of large data amounts the way it is usual today. It is also noticeable that USB and IEEE 1394 are having a "neck-and-neck race" concerning the data transfer speed, despite of the fact that long time ago USB outperformed Firewire in popularity.

Serial ATA, also called SATA is actually a data bus in the PC that communicates the processor with the hard disk or other drives. By the expansion to eSATA-Bus (External Serial ATA Bus) it is also possible to connect some external devices to the PC through the SATA-interface. This possibility is mainly used by external hard disks or memory sticks.

Comparison of USB- and Firewire-interface

USB means Universal Serial Bus; it was introduced into the market in the year 196 by the companies Intel and Microsoft. There are two other firms behind the name Firewire: Apple and Sony. While apple uses the name Firewire, Sony uses the name iLink in case of an IEEE 1394-interface.

How could a company as Apple get a foothold into the well protected Windows-world of Microsoft with its Firewire interface? The reason for that is in those years up to 2002, when USB only existed in the version 1.1. With a data transfer rate of 0,2 MByte/s, USB 1.1 was simply much too slow for many applications; then Firewire was a more powerful alternative with 50 MByte/s.

When USB 2.0 was introduced in the year 2002 into the market, with a speed of up to 60 MByte/s, it outperfomed Firewire IEEE 1394a with 50 MByte/s, but the version IEEE 1394b of Firewire is currently the faster variant with 100 MByte/s. But anyway, the USB 2.0 Hi-Speed and the Firewire can be considered to be more or less equal, as those values are only theorically achievable and in the practice of course other components play a role in the transfer speed. Both interfaces are also hot-plug-capable, this means that another device can be also connected to it without having to switch off the computer.

Concerning the speed, USB 2.0 and Firewire IEEE 1394a are approximately on the same level. With a data transfer rate of approximately 40 MByte/s in practice, they transfer a 35-mm image scan from the scanner to the computer in approximately 10 seconds.

Both USB and also the Firewire interface offer the advantage that they also provide the external devices (as for example the keyboard or the mouse) with current. In this concern, Firewire is ahead, as with 1,5 ampere it permits three times more current flow than a USB interface. This is specially advantageous in case of external hard drives, as then they do not need any power supply at all. For example, the reflecta-slide scanner x-Scan, x²-Scan or x³-Scan are exclusively supplied with current by the USB-connection.

Concerning the maximum cable lengths, the difference between Firewire and USB 2.0 is significant. Although in both systems it is easily talked about a maximum length of 5 m, a USB cable - depending on the design and quality - is basically extendable, even though by applying some tricks and having a little experience and/or the respective background knowledge. In case of the Firewire-generation IEEE 1394b, it is talked about a possible range of 100m.

Is there actually a winner between the USB-interface and the Firewire-interface? On the market, USB clearly dominates. Today, almost every computer has numerous USB-connections, while many times, the Firewire-connections are only available through some Firewire-cards. Nowadays, the consumer devices almost only have some USB-interfaces for connecting them to the computer; only in the video sector there are still numerous devices that are connected to the computer exclusively through a Firewire-interface. Is there a winner between USB and firewire in the film scanner sector? Almost all film scanners only have a USB interface, only some few professional devices do have an IEEE 1394 Firewire-connection for the connection to the computer.

The remaining question is what the future will provide, do some new generations of interfaces in the film scanners make sense? Either the Firewire- as also the USB-standards are further developed. With the IEEE 1394-2008 standard, there is a new Firewire-interface with a data transfer rate of 1,6 GBit/s (version S1600) and/or 3,2 GBit/s (version S3200). The USB 2.0 interface will get a successor with the USB 3.0 with the epithet Superspeed. USB 3.0 is specialised for a data transfer rate of up to 5 GBit/s.

Do these new interfaces that are approximately 10 times faster make sense in the case of the film scanners? Let us have a look on our page Image sizes and data sizes of scans. From these tables we see that a 35-mm image scan of 4000 dpi maximally generates about 120 MB of data that have to be tranferred over the interface. Many scanners that work with nominally 7200 dpi (but many times do not even achieve 50% of this value in practice) generate some image files up to 500 MB. The transfer of such big amounts of data takes in case of a USB 2.0 and/or IEEE 1394b interfaces about approximately 10 seconds; this time can be reduced by approximately one second with USB 3.0 oder IEEE 1394-2008. This certainly sounds good; but considering that a scan with 7200 dpi takes a quarter of an hour with many scanners, then it gets clear that the speed of the interface does only play a second role in the scan speed. This is why my conclusion is as follows:

USB 2.0 and Firewire IEEE1394a are fully sufficient for a film scanner. USB 3.0 and IEEE 1394-2008 certainly have a data transfer rate that is 10 times faster; but the resulting time advantage does not play a significant role in view of some huge scanning times.

Thus, when buying a film scanner or a flat bed scanner one should pay attention that the device has an USB 2.0 or a Firewire IEEE 1394a/b interface. An USB 1.1 interface is much too slow for the transfer of big data files. USB 3.0 and/or IEEE 1394-2008 certainly shorten the data transfer time up to a factor of 10; but the total time for a scan of a high resolution only reduces insignificantly.

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