Leveraging Pixel Shift for Art Copy Work
Art of Copying Art
Art copy work is certainly not the most exciting work I do, but lately I've been doing a bunch and I've fought through some technical challenges and hurdles to arrive at a repeatable process that works great. And I found that to be, well, fun.
Caveat: while this is a specific article about photographically duplicating artwork, it has some very vendor specific tools and techniques. Some of these things are optional and others are replaceable with equivalents found in your technical world.
Setup - In my case, I'm using:
- Sony A7rIII camera (42mp, optionally using Pixel Shift for maximum sharpness)
- Voigtlander 65mm f2 macro lens (a ridiculously sharp manual focus lens)
- Sony Imaging Edge Desktop software (optional) + CaptureOne Pro 20
- Flashpoint (Godox) flash gear and an "R2" radio trigger
- Pola-Glare polarizing filters for the flash units and a polarizer on the lens.
- Topaz AI Gigapixel (for upsizing, if required. It's just awesome)
The chances of you using the same stuff is pretty remote, I get that, but the concepts are unique to the equipment I employ. Hopefully a Canon user using Lightroom and/or Photoshop will get something out of this too.
A local artist, Erin McGee Ferrell, is a prodigious painter. She landed some licensing deals with art dealers and as the dealers decide to carry her work, they need digital copies to print and resell. Erin's iPhone wasn't cutting it so she called me.
As a cancer survivor with double, maybe triple the energy of anyone I know, Erin's hard to keep up with and produces paintings constantly.
The other day she showed up at my studio with 30 pieces to copy and about 16 were for an art dealer with very specific (huge) image size requirements.
That's a Large File !
The large file requirements really sent me for a loop. One painting they liked was 6' x 6'painting and they wanted a full size digital at 300 dpi resolution. That's 21,600 x 21,600 pixels!!!! I pondered stitching and struggled with how I'd shift the camera (or the painting) and not send something off kilter.
If I could do it without stitching, I wanted to try.
To get there, I identified three tools (two of them new to me), for my toolbox: Pixel Shift, Polarizing sheets (which I had already) and upsizing software.
Three Extra Tools in the Toolbox
Pixel Shift Multi-Shooting
Max out the details? Why not!
Pixel Shift is made for art copying work because it works best with a non-moving, cooperative subjects. Depending on the camera body, it can come in two basic flavors (or it may not come at all). The first type, 4-image, results in a standard size image (the normal dimensions produced by the camera body, in my case - Sony A7R3 - that's 7952 x 5304) but with sharper detail. The second type, 16-image pixel shift, actually creates a 4x larger image with , well 4x the detail and size. My current body, the Sony A7Riii, allows only for the first option, so while I cannot generate a 241 mega-pixel image like the latest A7RIV, I still want all the sharpness I can get: 4-image Pixel Shift is what it will be.
In "Pixel Shift Multi Shooting," the camera shoots four uncompressed RAW images while shifting the image sensor one pixel at a time. You can generate images with a higher resolution than is possible with regular shooting by combining the four RAW images on a computer using the Imaging Edge Desktop application. This is helpful when shooting still subjects.
See this Petapixel review of Pixel Shift for a more detailed discussion.
Note: Pixel Shift should work well for any static subject (architecture, a piece of art on an easel, still life images). And since I'll have to upsize later to meet some of my projects requirements, the extra sharpness offered by Pixel Shift can only help my cause.
Other mirrorless vendors are introducing or have introduced similar tech, I know Panasonic, Ricoh and Olympus had an equivalent to Pixel Shift before Sony and I wouldn't be surprised if it's coming in the Canon and Nikon mirrorless worlds too.
The only drawback to Pixel Shift I found was the need to add another software application to my normal workflow. In my case, as a Capture One Pro user, I needed Sony's Imaging Desktop applications (EDIT, REMOTE and VIEW) to create the Pixel Shift image. I always found Capture One to be the gold standard for tethering, but it is unable to compile a Pixel Shift image. The good news is that the Sony REMOTE app triggers the camera to take all four shots and auto-generates the combined ARQ raw file (the Pixel Shift raw file: the aggregate of the 4 source .ARW raw images) ... all in a single click.
Note tethering is optional: you don't need to tether as you can shoot the pixel shift images in camera and combine them later using Imaging Dekstop EDIT. I prefer tethering as it's just so much faster.
The Sony EDIT app can be used to set white balance as appropriate and output a full size TIFF. I'll say with confidence that the while Sony software is certainly no Lightroom or Capture One, it didn't take long to learn it and I appreciated the realtime LCD preview that appeared one my Macbook pro. Came in handy when using REMOTE to check focus and alignment.
Bottom line, the Sony software works and didn't slow me down much once I got used to it.
Polarization at the light source:
The thing about art is that it's not always straight forward. By that I mean, you don't know what you'll get: will the piece have glassy or glossy elements that reflect light from all over and show up as glare in the capture? It very well could and it makes sense to plan for that.
In my case, some of Erin's pieces have either glass-like elements or sections of very glossy paint. These can cause havoc on a photo because of the way those areas reflect. To solve that, I found some reasonably priced polarizing sheets at Adorama. These "pola-glare" filters worked quite well for me. The can be rotated for effect by simply unclipping and turning.
The Lens Matters: I shot with a Voigtlander 65 macro lens which is just a fantastically sharp, sluggish, manual focusing, heavy and bulky piece of glass... and it was perfect for the job.
(phillipreeve.net review says: Just wow! I have never before tested a lens with such great results. The Voigtlander 2/65 APO is excellent across the frame from wide open with only the slightest bit of falloff towards the corners... I think I haven’t found so little fault with a lens before.
There are many high quality macros out there that fit the bill, but certainly you need a lens that is sharp corner to corner which doesn't suffer from field curvature. In fact, you probably don't need a macro at all (unless your copying very small art of course). But if your image will be upsized, the sharper the better. Stopping down will help keep it all in focus should you not be 100% perpendicular to the art.
On the front of the lens I stuck a standard circular polarizer (obviously not shown here). Some people recommend linear ones, but the circular polarizer did a good job of allowing me to max-out or reduce the polarizing effect with a quick rotation.
At the end of the day, I've found that part of the "art" of copying art is about dialing-in or dialing out the amount polarization.
More on that below....
I don't believe there's a right answer as to how much polarization to employ; for me it's usually "more than none" and "less than the max" as it's more about using the amount appropriate for a given painting. I found you can literally "over polarize" some paintings, removing visibility of the actual brushstrokes, details you might want to keep visible.
Polarization can also increase the perception of saturation in the painting beyond what you see in normal light. My only advice is to experiment a bit and find what levels of polarization suits the piece of art being copied. If possible, get the artist's input.
To adjust polarization, you can remove the polarizing filter from the camera lens while keeping the polarizing sheets on the flash units. It's sort of a half-way point between max polarization and none. Personally I tended to leave the circular polarizer on the lens and rotate it to maximize or diminish some of the effect.
Obviously, some artwork may be very flat and lack glossy elements (e.g water colors paintings on thick matte paper) and may not suffer from any reflections at all. In those cases you may not need any polarization.
One of Erin's art licensors wanted one or her paintings, a 72" x 72" beast (not shown), copied so it could be printed life size ... resulting in a digital image capable of 300dpi printing (e.g 21,600 pixels squared!). At that size - over 450 megapixels! - I don't care which camera is in hand, you'll have to upsize or stitch a multi-shot pano of some sort.
Honestly, I'm not sure the requirement to print at 300dpi makes all that much sense for a 6' print (rules of thumb usually say you can print at much less than 300dpi when viewing distances increase). But it wasn't for me to decide, plus I thought it interesting to see what I could do.
Granted, most reasons for upsizing disappear with the 61 megapixel A7RIV and 16-image Pixel Shift (which makes a 241 megapixel image). But on this day, for this particularly huge painting, I don't own one of those so upsize I would! (Nor do I own a 100mp medium format rig).
Having done little serious upsizing in the past, I first researched options online. The usual suspects (Photoshop, Affinity Photo, Gimp) work pretty well in my experience as they use processing methods like Bicubic, Nearest Neighbor, Bilinear etc., but I eventually landed on Topaz's AI Gigapixel after only hearing high praise from pro photographers in various forums. I don't know what their secret sauce is and honestly, I don't care ... a long as it works. (I find the term "AI" to be overused these days, but maybe not in this case?)
After installing the 30 day trial, I compared some 2x and 4x upsized images and it really impressed me. Lacking time to do any exhaustive comparisons, I'd seen enough and bought it for $99. Seriously, if you have any upsizing needs at least kick its tires for free for 30 days and run some images against it; decide for yourself.
I delivered an original 1x sized TIFF and a 4x, Gigapixel upsized TIFF to the art licensor. They had done their own 4x upsizing using my original (normal sized) TIFF using Photoshop and greatly preferred my Gigapixel version.
That was enough for me, ... moving on.
The example below is a 2x upsize of a different image using AI Gigapixel. (Painting by Erin Ferrell)
Here are two crops:
Workflow: the Full Monty
Polarization --> Sony Imaging Edge (for pixelshift) --> CaptureOne (edit) --> AI Gigapixel (upsizing)
So let's pull out all the stops and shoot. I've found shooting artwork is hardly ever the same each time. You may not need to upsize a particular piece and thus you can skip the last step. Likewise, it could be a watercolor on paper that has no reflective surfaces and you may be able to skip polarization.
But In this case, I had some pieces with glossy paint in spots and even some with glass-like shapes embedded in the canvas; and add to that the need to be blown up to gigantic dimensions.... so I needed all the tools in my toolbox. I'll call it the "Full Monty".
Keep in mind, I tether a lot already using CaptureOne Pro (C1), but in this case I'm inserting Sony Imaging Edge Desktop REMOTE and EDIT software up front to perform some of C1's normal duties and then others only Edge Desktop can perform. I used REMOTE and EDIT for tethering/remote triggering, raw processing, generation of the 4-shot pixelshift raw image and finally converting that image (a .ARQ file) to TIFF and sending it to a Capture One Pro "Session" folder (the sessions internal "capture" folder to be exact). Lightroom users could front end Lightroom in a similar fashion.
This workflow looks something like this ...
Step By Step
In more granular detail, it looks like this:
- Put polarizing film sheets on flash heads (I use Flashpoint/Godox with the R2 trigger)
- Put polarizer on lens.
- Take test images, pixel peep, and adjust polarization to taste.
- Shoot in the sharpness sweet spot of the lens you're employing (usually f5.6 to f11) and make sure you shoot perpendicular to the artwork.
- Fire up Sony Imaging Edge REMOTE and tether to your camera
- Shoot gray card for WB on a single test shot and save that setting to a setting file using Imaging Edge EDIT
- Shoot the 4-image Pixelshift file (which generates an .ARQ file)
- Apply the gray card WB setting you just saved to the Pixel Shift ARQ image.
- Use EDIT to output the ARQ file to TIFF , placing it in the Capture One Pro Session's "capture" folder (you can also manually copy the TIFF in there later.) I love C1's sessions because there is no "import" step like a C1 (or LR) catalog.
- Jump into C1 and crop and adjust contrast, etc, as needed (or substitute your editor of choice) and output full size TIFF.
- Upsizing: if needed I used Topaz AI Gigapixel. It does a superb job.
Final notes and caveats:
- When shooting Pixel Shift composites, set the pause between shots so as to give your flashes enough time to reset. I used 3 seconds, but 2 would have worked.
- Don't move. Literally... don't move. The camera is shifting by one pixel to take each shot, vibrations in the floor, loud music with lots of bass can vibrate the camera and ruin your Pixel Shift efforts
- I used full electronic shutter. Now, what's interesting is that I normally couldn't do that with my camera and my Flashpoint/Godox R2 triggers. There's probably some fine print somewhere, but it just wouldn't let me. But with Sony Image Edge REMOTE running the show, I was able to use full electronic shutter. Why use it? Mainly to minimize shutter vibration for the Pixel Shift composite. Of course, I could have used a mechanical shutter and I'm sure it would have worked fine, but since I got full silent mode to work, I stuck with it.