- Warms the painting.
- Some light is reflected and diffused from the surrounding objects, and so is quite difficult to obtain a pure transmittance image.
- Not so easy to handle.
- LEDs produce narrow light spectra, so generally you don't need a IR-PASS filter in your camera, this means that theoretically you could generally achieve a better MTF.
- There are available different type of IR LEDs operating in different NIR region (940 nm, 850 nm etc. etc.) so basically you can build cheaply a multispectral imaging system. Or even multispectral polarized imaging system...
Suppose you are in a completely dark room recording a video, the painting appear black in the area where is not lighted, moving the lamp when a different area is lighted the pixel values increase. So when you scan the painting surface with your lamp, keeping your lamp at a fixed distance basically what you need is to substitute the unlighted with the lighted ones. So the algorithm compare the same pixel and keep the highest value. You can compare the same pixel of an acquisition with the next acquisition or you can set a threshold (something like: if pixel>background and pixel < 255: result_pixel=pixel). The first solution is quite simple to achieve using Python, keeping all the snapshot in a folder you can use this script:
// Comment from PIL import Image,ImageChops from os import listdir,sep def FolderElab(): foldername=r'/home/giacomo/Documents/Foldername' folder=listdir(foldername) fused=Image.open(foldername+sep+folder) for i in folder: orig=Image.open(foldername+sep+i) fused=ImageChops.lighter(orig,fused) return fusedI've used an old 0.31MP webcam after removing the ICF and substituting it with a piece of floppydisk (as mentioned earlier you can use it without an IR-PASS filter, however sometimes could be easier install one to operate in lit rooms). This is the first result, merging all the images.
|Resulting image made of different images as the previous one.|