algorithm - Detecting individual images in an array of images -


i'm building photographic film scanner. electronic hardware done have finish mechanical advance mechanism i'm done.

i'm using line scan sensor it's 1 pixel width 2000 height. data stream sending pc on usb ftdi fifo bridge 1 byte values of pixels. scanner pull through entire strip of 36 frames end scanning entire strip. beginning i'm willing manually split them in photoshop implement in program me. i'm using c++ in vs. so, need find way pc detect near black strips in between images on film, isolate images , save them individual files.

could give me advice this?

that sounds pretty simple compared things you've implemented;

  1. calculate average pixel value per row, , call resulting signal s(n) (n being row number).
  2. set threshold s(n), setting below threshold 0 , above 1
  3. assuming don't know exact pixel height of black bars , negatives, search periodicities in s(n). describe in following total overkill, that's how roll:
    1. use fftw calculate discrete fourier transform of s(n), call s(f) (f being frequency, i.e. 1/period).
    2. find argmax(abs(s(f))); f represents distance between 2 black bars: number of rows / f bar distance.
    3. s(f) complex, , has argument; arctan(imag(s(f_max))/real(s(f_max)))*number of rows give position of bars.
  4. to calculate width of bars, same second highest peak of abs(s(f)), it'll easier count average length of 0 around calculated center positions of black bars.
  5. to exact width of image strip, take pixels in image border may lie: r_left(x) signal representing few pixels in actual image might border filmstrip material, x being coordinate along row). now, use simplistic high pass filter (e.g. f(x):= r_left(x)-r_left(x-1)) find sharpest edge in region (argmax(abs(f(x)))). use average of these edges border location.

by way, if want write source block takes scanned image input , outputs stream of pixel row vectors, using gnu radio offer nice method of having flow graph of connected signal processing blocks want, without having care getting data b.

i forgot add: use resulting coordinates opencv, or other library capable of reading images , specifying sub-images coordinates saving new images.


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