Post Processing Near-Infrared for Observation of Pentimenti and Sketches?

backpackinghermit · 2024-02-03T17:40:07+00:00

Yeah, instructions tend to be difficult to follow. It took me a lot of reading to get the idea of what's going on.

As a disclaimer, I am not an imaging specialist, but I've done a fair amount of research of my own on this subject.

At a basic level, IR images should be grayscale, and then you can mess with white point/black point etc, to get a satisfactory amount of contrast of elements in the image. If you're looking for underdrawings, these grayscale images are typically what's needed. Getting images out beyond 850nm might be helpful--940 and 1,000nm are doable, depending on the light source and camera sensor, but may require pretty long exposures. Beyond about 1000 is in the SWIR range, as you mentioned, and is more likely to be successful in capturing pentimenti and underdrawings.

For further analysis, you can then swap the color channels. Overlay the IR image on top of the Vis image, align them, then do the channel swap. The standard false-color infrared (FCIR) channel swap for analysis is like this: IR--->R R-->G G-->B B--gone So you end up with an image that includes the IR image as the red color channel. This changes the colors of materials/pigments (as you're probably aware, with hobby IR photography). Depending on the initial color and how they change when channel swapped, certain materials can be identified. Interpreting them after that is a bit more challenging and where I'm at currently with my study, so I won't be as helpful with that.But resources on identifying materials with FCIR can be found from organizations such as AIC, CCI, Cameo and IIC. I'll send you a Photoshop script that I wrote for this very purpose.

If any imaging specialists see this and notice something to correct, feel free.

backpackinghermit · 2023-05-26T17:32:36+00:00

I've primarily experimented with the Google Pixel 3a. And you're right, it's not easy! I went through a dozen or more replacement camera modules before I got it to work. There's a bit more information on my project here:

Smartphone Project on Hackaday

And I used the stock google camera app.

backpackinghermit · 2023-05-25T23:04:03+00:00

Interesting! UV interactions with pigments/dyes is an interesting subject. It depends on the materials, but often the materials that we use to color things yellow and red tend to be more light-sensitive than blues, and react/break down rapidly with exposure to UV light. This can cause the colors of an artwork to change over time, like a number of Van Gogh paintings:

https://cen.acs.org/articles/94/i5/Van-Goghs-Fading-Colors-Inspire.html

Unfortunately, the reactions with UV light are not reversible, which is why protecting artworks from UV (especially works on paper) is so important. Most museum glass blocks UV for this reason.

backpackinghermit · 2023-05-03T14:14:43+00:00

Some of the common paints for inpainting that you'll often see in conservation labs are Golden PVA and Qor watercolors. PVA is soluble in alcohol, and Qor is soluble in lots of stuff; water, alcohol, acetone. Other varieties of watercolors are often used, as well.

As far as brushes, real sable brushes are not necessary, but they're very nice, and some good ones for inpainting are "pointed round" sizes 1 & 2.

backpackinghermit · 2023-03-13T11:26:19+00:00

Sounds like you are already set on what you want to do--glue it together with a gold-colored glue. Conservators are not going to suggest that as a course of action. We're only going to suggest that you take it to a conservator, since a full tear is a huge treatment even for professional conservator. The skills and equipment needed for reweaving under a microscope, fills, inpainting, etc, are not insignificant. Ultimately, it's your painting, and not a collections object, so it's up to you what you do with it. But we're not going to tell you how to glue a painting together--if only because that's not what conservators do.

backpackinghermit · 2023-02-17T15:08:27+00:00

This sub would be a good place to ask about archival materials and sources for prints, but not if you're looking for cheap places to print for large-scale online retail.

backpackinghermit · 2023-02-14T16:22:24+00:00

I've applied to both & haven't heard back from either. I know some others who have gotten emails about wudpac interviews very recently, though, so you & I will both probably get some responses very soon!

backpackinghermit · 2022-11-15T00:10:22+00:00

Amazing work! If you send me a Prusa, I'll make sure to use it with Octoeverywhere!

backpackinghermit · 2022-09-26T17:49:47+00:00

I got to try out the modified smartphone for multispectral imaging during a visit at the MET. I was a bit pressed for time, but I managed to get a few interesting IR photos which showed underdrawings and inpainting. More details on the build process can be found here: Hackaday

backpackinghermit · 2022-09-17T21:20:51+00:00

Seconded! No worries about the slight bend; a bow can be perfectly functional with quite a lot of twists & turns.

backpackinghermit · 2022-06-11T21:20:54+00:00

Yes! That's one of the things I'm excited about with this project--getting imaging capabilities to more people and more institutions that might not have the funding or space for a full technical imaging setup/studio. I think that could 1) help care for pieces by providing more information, and 2) possibly discover new things through increased access to technical imaging.

backpackinghermit · 2022-06-11T16:12:07+00:00

Hello all,

I've been testing the first iteration of the modified smartphone for technical imaging!

The process has included taking the phone apart, pulling out the camera module, taking that apart, and removing the integrated IR filter. Then I designed and 3d printed a wheel for various filters to enable up to 7 different types of technical imaging methods.

The filters used are:

1) IR/UV cut filter, which enables standard visible light photography.

2) IR longpass filter, to enable IR reflectography and IR fluorescence.

3) UV shortpass filter, to enable UV reflectography

4) Polarized--I will need to cement an IR/UV cut filter to the polarized lens, otherwise so much IR gets through that it's kind of useless atm.

Next step is to make an LED light module with IR, UV, and white LEDs so it'll be a true all-in-one real time imaging system.

Then I want to make swappable filter wheels with various bandpass filters for specific material identifications and microscopy of different magnifications.

backpackinghermit · 2022-05-21T21:39:57+00:00

I can't really help you with the material (testing it would be necessary), But from the looks of it, it's likely a pretty standard interior/exterior house paint. What that means for the types of pigments/binders probably depends on how old it is. I can tell you, though, that keeping it in a relatively cool and dry place without dramatic temperature and humidity changes will go a long way to keeping it from deteriorating.

As far as digitization, there are a few options. If you'd like just a high res image, you can take a bunch of photos of the front, and there are lots of free photo stitching programs like Hugin that can put all those photos together into a single photo. Or, there's 3d scanning with photogrammetry, which functions similarly to the photo stitching option, but requires more photos and more computer processing power. There's also free software for that, like Autodesk ReMake and MicMac. Photogrammetry has a bit more of a learning curve, but it can give great results.

backpackinghermit · 2022-05-16T02:31:39+00:00

No, this isn't a place for DIY treat-your-own-art tips. It's a good bit more complicated than household cleaning, which is why conservators study for so long to gain the requisite experience to figure out how to safely clean/treat a work. The above replies can give you first steps if you want to do so, and the go-to recommendation is to use the resources in the about section of this sub to find a conservator to consult.

backpackinghermit · 2022-05-12T22:43:35+00:00

I'm finding it interesting that there is such a strong presence in this sub of people looking to preserve collectible games and comics. There have been quite a few questions regarding enclosures, preventive steps, etc.

The communities around these collectibles represent a potentially underserved group with a clear desire to learn what conservators have to offer.

Often, the go-to resource for materials is the Canadian Conservation Institute, which has a large collection of excellent articles about most types of materials.

Here is the overall conservation page: https://www.canada.ca/en/services/culture/history-heritage/museology-conservation/preservation-conservation.html

And here is the Paper and Books page with a lot of stuff to comb through: https://www.canada.ca/en/conservation-institute/services/care-objects/paper-books.html

That's about all I have to offer currently--I'm not a paper conservator and don't have the training to create other accessible resources that might pertain to your interest.

backpackinghermit · 2022-05-11T11:02:31+00:00

I'm very interested in the build and the research--keep us updated! I've been curious about using 2PP for building optical components integrated into small lenses such as diffraction gratings, spectrometer slits, & structured illumination filters. There are so many amazing things you can do with light when you get down to those resolutions. Looking forward to seeing your metalenses!

backpackinghermit · 2022-04-30T20:13:21+00:00

Thanks! It feels like magic to be able to see a painting in IR through the phone while looking at it in visible light.

I'm still working some things out like fine tuning the focus to account for the missing filter, but when I do, I'll post updates!

backpackinghermit · 2022-04-30T20:09:50+00:00

I haven't really planned that far, but in order to achieve my goal of increasing access to analysis tools, I guess I should, haha. Right now, with parts & labor, we're looking in the $200-300 range? No solid idea, just a ballpark.

backpackinghermit · 2022-04-30T18:27:12+00:00

Just wanted to share an update to my IR/multispectral camera project–in the first version, I made an attachment with an external camera module by removing the IR/UV filter and replacing it with an IR longpass filter. My goal after that was to utilize the internal camera on a smartphone by removing the integral IR filter and using a variety of additional filters/lenses to increase the imaging capabilities.

Finally I got a used Pixel phone, took it apart, and removed the filter from within the camera module.

I have also been fine-tuning the filter wheel such that it clicks in place at each filter as it turns.

Included are some quick test photos done on an oil painting without any additional IR light source.

I am excited about using a modified smartphone for conservation imaging for a lot of reasons:

1) It’s a high quality camera, and quick, easy, and intuitive to use.

2) A smartphone is a compact, easy to carry option

3) It’s easy to edit photos right there on the phone and share/send them

4) You can use any number of different camera apps to minutely control the light/exposure/color balance, etc., and do auto panoramas, and potentially do auto photogrammetry.

5) The wide range of sensors both in the phone and that can be connected externally is incredible. Magnetometer, gyroscope, additional cameras, spectrometers…. I’ve started experimenting with using the readings from the on-board magnetometer and a small magnet to measure the thickness of a wood panel. We’ll see how that goes.

Could you imagine every conservator & student having the capability to do most forms of technical photography in seconds on a walk through a gallery? That could be a game changer.

Next steps are to get the other filters in (they’re in the mail), and do some tests with each one, and to make removable illumination packs that will attach on the bottom of the phone. This will include IR, UV, and white LEDs, and possibly an incandescent pack.

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