Plustek OpticPro A320 flatbed scanner repair - Page 1
Forum section: electronics / repair

author: Pinörkel
author_rank: Regular Contributor
timestamp: July 18, 2025, 06:12:15 pm
content: Hello,I recently bought a used Plustek OpticPro A320 A3 flatbed scanner. Unfortunately I noticed during an in depth analysis of the scan quality that all scans taken above 800 dpi had a strange vertical blur on them, making them much worse than actual 800 dpi scans.This was a disappointment, since I specifically acquired the scanner for its optical 1600 dpi resolution. I immediately suspected something with respect to the carriage or the carriage drive to be defective or in need of adjustment, but I could not find anything loose or suspicious. The belt is still well tensioned, since it is tensioned by a metal spring, resembling the ones in spring loaded clothespins. Since the horizontal sharpness is not visibly affected, I suspect that there is no focus issue, but kind of a timing problem. The internet does not seem to have much information on what scan quality can be expected from the OpticPro A320 or on flatbed scanner artifacts in general.Thus, I contacted Plustek and got the answer that the CCD sensor needs to be re-adjusted. However, they will not do it because the service period for the scanner model has expired and claim the scanner to be beyond repair. With this information, I expected one of two possibilities. The first one was a mechanical adjustment which had to be measured via a calibration device. The second option would be some kind of calibration software that uses the scanner and maybe some calibration patterns to derive adjustment values which need to be written into the controller of the scanner. So, I asked Plustek if they could at least provide the adjustment documentation, which I was sure, should exist, but they refused and hinted at the scanner needing to be adjusted with a customized software that is not publicly available, has no publicly available documentation and very sadly cannot be provided.While digging through the web, I stumbled across a non-searchable, 145 page calibration wizard user manual from Novanta Photonics / Cambridge Technology (https://novantaphotonics.com/calwizard_manual/). What a lucky coincidence: on the list of supported flatbed scanner models was not only the Canon Canoscan 9000F, but also my Plustek OpticPro A320 ... The calibration software seems to adjust basically for any imaginable hardware inadequacy the systems of the scanner might have due to unavoidable hardware tolerances. This includes a distortion field correction and focus adjustment, center focus offsets and the like. The only thing that seemed to be related to adjusting timings was a laser / galvo timing adjustment. This puzzled me, because I didn't remember flatbed scanners to contain a laser or rotating mirrors. Maybe there is an external laser calibration fixture that needs to be employed here?My initial hope was that I could get my hands on the calibration software, read out the existing calibration and fiddle with the timing adjustment values to get the scanner back into alignment. Most of the adjustable parameters of my scanner, like distortion field correction and focus adjustment, seem to have usable values. And, the scanner basically works at 800 dpi and below. Has anyone here experiences with the process of flatbed scanner adjustment and could shed some light on what values most likely need to be adjusted in this case and, aside from the respective calibration software, what may be needed for readjusting this specific aspect of the calibration? Any help with this would be appreciated.

author: Uunoctium
author_rank: Frequent Contributor
timestamp: July 18, 2025, 06:23:15 pm
content: I'm not sure but i fear the Novantaphotonics document is related to laser markers esp the scanning heads with galvos

author: Pinörkel
author_rank: Regular Contributor
timestamp: July 18, 2025, 06:54:58 pm
content: Quote from: Uunoctium on July 18, 2025, 06:23:15 pmThank you for the reply. So, you mean flatbed scanners are only used in that document to calibrate galvo scanning heads and the calibration of flatbed scanners described on pdf pages 107 ff. is only an external distortion calibration for the scanners to be used for scanning head calibration afterwards. Me having misinterpreted that manual would explain several confusing things.

author: Pinörkel
author_rank: Regular Contributor
timestamp: July 18, 2025, 07:57:58 pm
content: OK, next attempt. Lets see what interesting stuff is on the control board.A M12L64164A-7T DRAM IC.A GL843 Scanner Controller IC. Thedatasheetseems to be quite informative and covers a lot of low level controlling stuff, but at first glance, nothing regarding calibration.A WM8196SCDS, an (8+8) Bit Output 16-bit CIS/CCD AFE/Digitizer. The datasheet is available viaMouser.A A3967SLB, a Microstepping Driver with Translator. Datasheet available fromhere.A 26 pin D-Sub-Connector that is only accessible when the board is removed from the case.I will have to dig into the data sheets, but at the moment, the GL843 seems to be the hottest candidate for me.

author: Uunoctium
author_rank: Frequent Contributor
timestamp: July 20, 2025, 03:39:22 pm
content: My humble opinion on this:The problem you described above cannot be solved by adjusting the hardware. The scanner comes with a native resolution of 800dpi. All resolutions above are artificial and nice marketing promises and rarely lead to an increase in sharpness or resolution.I looked into this a little last year as I had to scan several hundred unframed slides. I wanted to use a 9000F MKii flatbed for this (until this point only used for document scan) and found out more about the handling and technical details from the website:https://www.filmscanner.info/CanonCanoScan9000FMark2.htmlthan from the manufacturer (unfortunately only in German and only focused on film slide scanners).After reading the review it was immediately disqualified due to unacceptable scanning times and an outdated Plustek from the bay did this job because it came with Silverfast SW + licence. To avoid loss of sharpness caused by vibration i placed it during the scanning process on an 25kg granite plate w dampening feet and put an additional weight on top.The image you posted is exactly described in a Silverfast Leaflet about using the USAF 1951 resolution target for determine best actual usable resolution. The shown coloured image in 2.4 equals to yours and it seems that your scan is in RAW mode without dithering (or interpolation).https://www.silverfast.com/download/docu/6x7cmresolutiontargetdetaileddocumentation_en_2023-02-01.pdfSilverfast and VueScan offer software with extensive setting options for many scanners. You have to check whether this improves the resolution. In any case, the scan times and file sizes differ. Both need the manufacturer's twain driver installed.In my case, I would have been better off reading the review before buying. The introduction already states that the MKii uses the same imager as its predecessor and that Canon has dropped the very good Silverfast software that came with it and replaced it with its own.

author: Pinörkel
author_rank: Regular Contributor
timestamp: July 20, 2025, 08:40:58 pm
content: Thank you very much for the detailed reply.Quote from: Uunoctium on July 20, 2025, 03:39:22 pmHmmm, are you sure about the native scanner resolution? There are multiple variants of the OpticPro Scanner. There is the original A320(which I have), which should have 1600dpi and the newer models A320E and A320L with 800dpi and 1600dpi. At least regarding the horizontal resolution, my impression is that there is a step up from 800 to 1600dpi. I have not disassembled the carriage yet, because I do not want the usable 800dpi resolution to degrade and the model number of the CCD sensor could be only readable after desoldering it because it is usually printed on the back of the sensor.The datasheet of the GL843 scanner controller seems to natively support horizontal resolutions (matching the CCD sensor resolution) of 600, 1200, 2400, 3200, 3600 and 4800dpi, in addition to digital averaging of 1/2, 1/3, 1/4, 1/5, 1/6, 1/8, 1/10, 1/12 and 1/15. So, to get to usable 800dpi, the sensor should in theory at least support the lowest possible combination of 2400dpi and 1/3 averaging (the controller only supports averaging, not upsampling). Vertically, the resolution can be up to 9600 dpi for 2400 dpi scanners using quarter steps for the stepping motor.Quote from: Uunoctium on July 20, 2025, 03:39:22 pmFor slides, I tend to use a special setup with my DSLR, a diffusion filter and a flash, which greatly outperforms anything the Plustek OpticPro can do and gets me razor sharp 1900dpi without hardly any post processing (Yes, I know. Professional film scanners can do much better.). However, I wanted the OpticPro for distortion free A3 document and art scans.Trying to dampen the scanner vibrations is an interesting idea. During 800 dpi scanning the motor noises sound very smooth. However, during 1600 dpi scanning, the motor noised sound very stepped, which should indicate many small accelerations and decelerations of the carriage. The subtle vibrations of the scanner enclosure should counteract those vibrations, except when there is resonance. I will try to test if increasing the inert mass of the scanner has any visible influence on the issue.Quote from: Uunoctium on July 20, 2025, 03:39:22 pmThe example image in the SilverFast Leaflet seems to have been derived by downsampling the resolution to 50% and then upsampling to 200%, which gives a uniform interpolation error in horizontal and vertical direction. The vertical blur in my scans shows a different distinctive repetitive pattern that, for me, looks like it is related to some sampling timing issue. Nonetheless, an upsampling error should optimally disappear when downsampling the affected image again to an appropriate amount. If I determine the required amount with respect to the vertical dimension of the 1600 dpi images and downsample the horizontal direction respectively, I still get much worse image details than from the 800 dpi images. Also, there is still a subtle pattern in the images that I would not associate with the suspected kind of consecutive upsampling and downsampling.Quote from: Uunoctium on July 20, 2025, 03:39:22 pmI have tested scanning with the supplied twain software and with SilverFast9 to test the scanning quality. Both show the same issues with vertical resolution. I have fiddled a lot with the settings in SilverFast9 and the twain driver to kill as much post processing as possible and see the real sensor output, but nothing was able to improve the vertical resolution issues so far. Maybe I have missed something.In fact, it might be possible to employ a mathematical image deconvolution algorithm to tackle this issue, but for modelling that, one would have to acquire further knowledge about the technical cause of the issue. Or maybe, it would be possible to derive the deconvolution function from the scanner output and a known source signal. Seems like blind image deconvolution can be done to some degree via employing CNNs (e.g.link). This case would be simplified by the fact, that we already know the direction of the blur and the blur distribution uniform.Quote from: Uunoctium on July 20, 2025, 03:39:22 pmOf course, I tried to do some research before buying, but I have not found any scan quality tests on the web for the A320. The Epson Expression 11000 XL to 13000 XL A3 scanners most likely would have been a good option, quality wise. They even have an auto-focus feature. However, my usage frequency of the device would in no way justify spending 4500€ on a scanner, regardless if i could afford it or not.

author: Uunoctium
author_rank: Frequent Contributor
timestamp: July 22, 2025, 04:33:31 pm
content: tl;drI recall Sony's 2015 announcement regarding the end of production for all CCD imagers, which means your scanner is likely around 10 to 15 years old. Aside from the usual thorough inspection—checking for wear on the belt, belt tension, bearings, and hardened oil/grease, as well as re-lubricating—I wouldn’t recommend any hardware or software modifications.A more promising approach would be to apply smart algorithms:https://openaccess.thecvf.com/content/CVPR2024/papers/Zheng_Self-Adaptive_Reality-Guided_Diffusion_for_Artifact-Free_Super-Resolution_CVPR_2024_paper.pdf(link to GitHub repository included)

author: Pinörkel
author_rank: Regular Contributor
timestamp: August 01, 2025, 07:50:01 pm
content: There is no visible wear on the device and there were apparently also no lubrication issues since re-lubricating the device did not bring any improvement.Unfortunately, I discovered upon further scan quality investigation that consumer grade CCD flatbed scanners apparently, all have metrologically lousy scan quality. CIS sensor scanners are generally not suitable for my application due to the many merging artifacts ans the shallow depth of field.I found this out by noticing that the horizontal scale of my scanned documents seemed to be off by several millimeters. However, the vertical scale (in the direction of the carriage movement, seemed to be just right. After verifying that there was nothing wrong with my documents, I scanned a sheet of checkered paper (5mm grid) and made a comparison image with a 180° rotated copy of the scan overlayed. As can be seen in the attached image, there is a very pronounced horizontal barrel distortion which renders the scan practically useless for taking precise measurements. In addition to that, there is a small periodic vertical distortion, most likely related to the motor or gear movement, although I would not have rated this as a deal breaker. Upon searching the web for similar issues, I found many other users of CCD flatbed scanners experiencing this, hinting at this being a general issue of that technology.

author: Pinörkel
author_rank: Regular Contributor
timestamp: August 03, 2025, 04:00:48 pm
content: Regarding the CCD lens distortion, I had the impression that it should not be too difficult to calibrate this out in post processing. So I recorded a calibration image with a ruler, placed horizontally with respect to the scanner output. Then I wrote a small program that can automatically detect the horizontal positions of the ruler ticks with sub-pixel precision via low-pass filtering and quadratic fitting, construct a second set of reference positions based on the used scanner resolution of 800 dpi and the tick distance and horizontally undistort the image based on the two point sets. As can be seen in the attached image, this worked like a charm, despite being kind of slow, because I did not yet optimize the algorithm. In the overlayed image, the red ruler image is the original one, and the black one the undistorted one. Red and blue lines represent the detected tick positions.Interestingly, there was still a 1.5 mm overall size mismatch, which I could not explain until I noticed by scanning a tape measure that the scanning scale depends on the object distance to the scan window. As far as I believed to know the theory of operation of a flatbed scanner (stupid me), the viewing direction of the scanner should be perpendicular to the surface of the scan window. As can be seen in the attached image of the tape measure, this is not the case for the OpticPro A320. In theory, all tape measure tick lines should have been vertical, but this is only the case for the center of the image. Maybe this is a compromise they had to make, for putting the whole optical assembly, including the sensor, into the small carriage.Unfortunately, this is an issue which cannot be easily corrected for in the case of not perfectly planar documents, which was part of my initial motivation to get a CCD-based instead of a CIS-based flatbed scanner. Since CCD scanners are going out of production this year, because all suppliers stopped making this type of sensor, there is most likely no real solution to this.