Frequently Asked Questions - jareff-g/ALT-Scann8 GitHub Wiki

Table of Contents:

  • Question 1: How do I set up my Raspberry Pi to run ALT-Scann 8?
  • Question 2: Auto Exposure / White balance: What is the meaning of Match wait/Match margin?
  • Question 3: What is the use of stabilization delay?
  • Question 4: Should I use automatic white balance?
  • Question 5: Which other components (python or otherwise) are required to run ALT-Scann8?
  • Question 6: Is it a good idea alter the position of the camera while scanning?
  • Question 7: Automatic PT level is not working fine. Despite the photo-transistor levels visible in the embedded plotter being apparently correct, the levels shown in the spinbox appear too low, and frames are not detected at the correct position. What could be the cause?
  • Question 8: Before I start scanning a movie, which points should I check to make sure everything is ready?
  • Question 9: Frame detection issues, what are the possible causes?
  • Question 10: The film is not advancing one frame at a time. Instead, it appears to move a fraction of a frame, either upwards or downwards. What could be the reason?
  • Question 11: While scanning a film, I can see scanning speed variations as it progress. What is the reason for this to happen?
  • Question 12: The UI of ALT-Scann8 is too big for my screen maximum resolution. Do I have any options apart from replacing it with a screen supporting a higher resolution?
  • Question 13: In the average time spent statistics, I see that the times for AE/AWB keep increasing even when margin wait is disabled. What is the reason for this?
  • Question 14: When starting ALT-Scann8, I can see an error message 'QR Import issue'. Despite the error, everything seems to work normally. What is the reason for this?

Question 1

Q: How do I set up my Raspberry Pi to run ALT-Scann 8?

A: The following points describe how to proceed in order to be able to run ALT-Scann 8 in your Raspberry Pi (normall part of an already built T-Scann 8)

  • Your T-Scann 8 scanner needs to have been built with a compatible Raspberry Pi, and a Raspberry Pi HQ camera. ALT-Scann 8 has been only tested with Raspberry Pi 4 2GB and the HQ camera. Other cameras might work if they are supported by PiCamera2, but not guaranteed.
  • The Operating system on the Raspberry Pi needs to be Bullseye. Bookworm (newer) has not yet been tested, and versions older than Bullseye are (AFAIK) not compatible with PiCamera2, which is mandatory for ALT-Scann8. Even if you can use either 32 or 64 bit Bullseye, performance is much better with 64 bit, which is strongly reccommended (ALT-Scan 8 is not tested on the 32 bit version)
  • Once your OS is installed, you need to change a couple of things using 'raspi-config' (Interface options):
    • Enable I2C interface
    • Disable legacy camera support
    • Enable VNC (optional, if you want to handle the Raspberry Pi desktop from your main desktop)
    • Enable SSH (optional, same as previous but command line only, more tricky to configure)
  • On the Raspberry Pi, you have to install some additional software. Open a shell and run the following commands:
    • sudo apt-get install python3-tk
    • sudo apt-get install python3-pil.imagetk
    • sudo apt install python3-numpy
    • sudo apt install python3-opencv
    • sudo apt install python3-psutil
  • And that should be enough. In case of problems, open an [issue] and I'll try to help

Question 2

Q: What is the meaning of 'Match wait' and 'Match margin' in the Auto Exposure / White balance area?

A: When using automatic exposure, and/or automatic White balance, the HQ camera needs some adaptation time before adapting to the new auto-detected setting. At this point you have two choices:

  • Not enabling 'Match wait': In this case the frame will be captured immediately, before the camera had a chance to adapt itself to the new conditions (of exposure/white balance). So the captured frame (and maybe a few frames after that) might not be well exposed, or have the right white balance level. The camera will eventually settle on the new settings, and after a few frames captured images will be good again (unless the conditions of the film keep changing).
  • Enabling 'Match wait': In this case, before capturing the frame, ALT-Scann8 will wait until the camera adapts itself to the new detected conditions. Since in some cases this might slow down the process too much, you can use 'Match margin' to allow some flexibility. when 'Match margin' is zero, there is no tolerance: ALT-Scann8 will wait until the camera values (for exposure/WB) totally stabilize. Increasing the value from zero up to 100%, will allow a flexibility margin causing it to wait until a fraction of match is achieved (with 100% being the most permissive).

Question 3

Q: What is the purpose of the 'stabilization delay'?

A: When the scanner moves the film to reach the next frame, it is good, before capturing it, to wait for a short while so that vibrations derived from the scanner moving parts disappear. Normally 80 to 100 ms should be enough, but might need to be tuned for each particular scanner.

Question 4

Q: Should I use automatic white balance?

A: I'm no expert in photography, but from what I have found on the internet it seems using automatic white balance is not a good idea, as colors might get distorted. It seems that for the Raspberry Pi camera T-Scann8 uses the value of 2.2 for both the blue and red channels give a good result, but then I might be wrong. If you have better info on this topic please let me know.

Question 5

Q: Which other components (python or otherwise) are required to run ALT-Scann8?

A: In order to run ALT-Scann8 you need to install, at least (there might be others), the following components (these are the package names in Linux, in Windows or MacOS might be different):

  • python3-tk
  • python3-pil.imagetk
  • python3-numpy
  • python3-psutil

Question 6

Q: Is it a good idea alter the position of the camera while scanning?

A: No, it isn't. While scanning a film, it is very important not to alter the position of the camera in any way, otherwise it will cause problems later on in AfterScan to stabilize and crop the film.

Question 7

Q: Automatic PT level is not working fine. Despite the photo-transistor levels visible in the embedded plotter being apparently correct, the levels updated in the spinbox appear too low, and frames are not detected at the correct position. What could be the cause?

A: Increase the 'Fine tune' value. This used to be a problems with ALT-Scann8 versions prior to 1.8.33, due to the PT level to trigger a frame being too low with the fine tune at minimum. After 1.8.33 a minimum level is enforced to guarantee detection in any case. To complement this information, below you can see how the automatic PT level feature works, adapting the threshold (in red) dynamically to the varying levels reported by the photo-transistor (in blue):

Question 8

Q: Before I start scanning a movie, which points should I check to make sure everything is ready?

A: Yes, there are a few things to double check, which are important if you do not want to realize your scan is useless when it is too late (specially if you are performing an HDR scan that can take more than 8 hours to complete):

  • Image size: To start with, make sure the image in your film fills as much as possible the camera sensor, not forgetting to keep the holes well visible (at least 50% of the hole should appear in the capture). Specially important when switching between 8mm and Super 8, since image size is quite different.
  • Horizontal position: Once the image size is what you want, make sure the image is well positioned horizontally by using the front knob in the film plate. The right part of the image should stay visible, same as the sprocket holes, that should have at least 50% of their width visible (as they will be used later by AfterScan to stabilize the frames). This step should be coordinated with the previous one
  • Focus: Make sure the image is well focused. Using the 'Real time display' and 'Focus Zoom' buttons carefully look at the image and move the camera (or turn the focus knob, if you build the focus helper I added in Thingiverse) until the image is well focused, and the grain is visible in the zoomed image.
  • Film type: Check you have selected the correct type (ALT-Scann 8 will not try to detect the correct type for you). If you have doubts about what film type you are dealing with, a visit to wikipedia may help
  • Stabilization delay: Use a safe value for this one (around 100 ms). Shaky frames resulting when taking the snapshot too fast after advancing the film are not evident in ALT-Scann8 preview, but you'll notice right away when you load them in AfterScan
  • Speed: It is recommend to start with a low speed (1), unless you know your scanner behaves well with higher speeds
  • Frames to go: Especially if you are scanning a long film, or performing an HDR scan it is interesting to enter the approximate number of frames in the reel you are about to scan, so that you have an estimated time to completion (you can find a table with the estimated number of frames based on reel diameter here)
  • And in general, check all the other options to make sure they match what you want to do, but the ones described before are the ones that, by experience, it is easy to forget, and realize only once it is too late :-(

Question 9

Q: While scanning, the frames are usually misaligned so that a full frame is not captured inside the image. What could be the reason?

A: There are several possible causes for this, listed below:

  • Not using a pinch roller: Absence of pinch roller greatly degrades the ability of the capstan to move the film reliably. Without the pinch roller it is only the film tension that creates friction of the film against the capstan, and this is not always perfect. You might try to use lower scan speeds (which might increase the tension a bit) but still the best solution is to install a capstan.
  • Using the manual mode of the frame alignment settings (Steps/frame, PT Level): Manually setting the values for 'Steps/frame' and/or 'PT Level' might work for a while, but sooner or later frames are going to be misaligned again. This is due to changing film conditions (specially on big reels made up of different smaller ones) or to changing hardware conditions (see next point). Setting both items as AUTO will allow ALT-Scann8 to dynamically adapt on the fly.
  • Dirty Capstan/Pinch roller: I recommend to clean the capstan and pinch roller (water and soap only) after one big reel has been scanned, to remove dust and particles picked up from the films. Not doing it might cause a loss of adherence, resulting in a higher number of motor steps required to advance a frame (this is specially true if not using a capstan). Setting 'Steps/frame' as automatic might compensate for this, but in any case it is always better to keep both elements clean.

Question 10

Q: The film is not advancing one frame at a time. Instead, it appears to move a fraction of a frame, either upwards or downwards. What could be the reason?

A: Most likely the film type configured in ALT-Scann8 is incorrect. If the apparent frame movement is upwards most likely you need to configure 'R8'. If they appear to go down, 'S8'. As a reminder, Super 8 (S8) film as one sprocket hole in the middle of the frame, while for Regular 8 (R8) the sprocket holes are positioned between frames. If still not clear you can check this picture from Wikipedia.

Question 11

Q: While scanning a film, I can see scanning speed variations as it progress. What is the reason for this to happen?

A: If you are using automatic exposure, or automatic white balance, and you select the 'Match wait' option, ALT-Scann8 will wait for the exposure (or white balance) to stabilize before capturing the frame. If your film has many contrasting scenes where the exposure or white balance might change, it will affect the scanning speed. If you want to avoid that, you can either uncheck 'Match wait', or increase the 'Match margin' value. However, doing that might cause the exposure/white balance adaptation visible in the resulting video.

Question 12

Q: The UI of ALT-Scann8 is too big for my screen maximum resolution. Do I have any options apart from replacing it with a screen supporting a higher resolutions?

A: You have two command line options that can help with that:

  • -b: Forces scrollbars to be added to ALT-Scann8 main window, allowing you to scroll to access areas of the UI that won't fit in your screen
  • -f: Sets the base font size of ALT-Scann8 UI (11 by default). By setting a smaller font size, the whole UI will adjust to it, so that you should be able to make it fit in screens with smaller resolution. However, this might cause some parts of the UI to be harder to read.

Question 13

Q: In the average time spent statistics, I see that the times for AE/AWB keep increasing even when margin wait is disabled. What is the reason for this?

A: The reason for those counters to keep increasing even if wait margin is disabled is because, even when wait margin is disabled, there is a fragment of time spent retrieving the current value of the exposure and white balance values in order to update them in the user interface. If you want to minimize that time you can do so increasing the 'Preview' module to reduce the frequency of UI updates (preview image and automatic exposure/white balance values).

Question 14

Q: When starting ALT-Scann8, I can see an error message 'QR Import issue'. Despite the error, everything seems to work normally. What is the reason for this?

A: The reason for that message is because in version 1.10.53 a new (optional) feature was added to display some debug info encoded in a QR Code shown in the UI (so that it can be easily included in a screen shot when reporting a problem). To avoid the message, and benefit from the new feature, you need to install the 'qrcode' library, using the following command: sudo apt install python3-qrcode