How to 'photoscan' large artwork canvases by combining multiple photos into single high resolution digital image without glare

Question

Have a number of large (4x6 foot/ 120x180cm) acrylic paintings that I want to capture digital images of that will be suitable for re-printing large replicas of the paintings. Ideally, want to capture digital images that are high-quality, high-resolution, well-lit, with little or no glare. Want to create images that are higher resolution than the resolution of the camera being used to take them by combining together multiple images. Since there are multiple paintings, I am looking for a solution that is efficient, not requiring too much time per image.

How should I do this?

There is an Android mobile photo app called PhotoScan that will do this automatically for images captured from an Android phone. The app directs the user to take 4 photos centered at 4 different places forming a rectangle on the artwork, and then the software automatically performs a stitching together of the different photos, deals with perspective etc, and appears to select the best lit from each of the 4 versions for each pixel to yield that pixel in the final image, which pretty effectively removes glare. It also does a good job of handling the different lighting in each of the four component images so that the image looks uniform in the hand. Unfortunately, this app only allows for taking 4 images, not more, allows little additional control, and does not work with images except those taken with the Android device/phone.

How can a similar approach, hopefully automated, be used to accomplish this with photos taken with a DSLR?

Adobe Photoshop Photomerge makes it possible to stitch together multiple images, and does some of the perspective correction, but as far as I can tell it does not appear to provide a way to automatically handle the lighting, glare, and other issues.

Is there a good way to do this?

Thanks

Answer 1

No app can change the lighting.

Photographing artwork for reproduction is a professional specialty. It uses well considered lighting in controlled conditions, high resolution cameras (often medium format), and lenses that cost "more than I paid for my first car" so to speak.

Multiple well placed lights plus a tripod for the camera is table stakes. A big space and a long lens makes placing the lights easier. The long lens reduces the angles which produce glare in the image. The larger space allows more distant light placements thereby reducing falloff from the inverse square law to even out the illumination.

The gear and technique need to be appropriate to the level of quality desired. A phone may or may not be sufficient depending on the goals for output and effort.

If quality matters a lot, it might be worth hiring a specialist. The top level of do-it-yourself, probably involves renting lights and camera gear. Below that you will probably need to invest a lot of time in fixing things with few guarantees that the input is sufficient to produce the desired output.

Answer 2

This will be a very basic guide.

I. Space

First of all, you need a lot of space. Space on both sides of the painting and space in front of it.

II. Lights

Put some good lights (Good CRI) at 45° of your subject. The further away the less fall off you will have (B) so the more uniform light you will get.

III. Lens

You need to stay far away from the painting to reduce distortions like barrel distortion (D). Use the longest focal length you have and a rectilinear lens.

Keep the lens perpendicular to the painting. Prepare the positions the camera will be in advance. You could put some reference marks on the floor and on some walls, and use some laser guide to align the camera.

IV. Stich

You can use Hugin with the mosaic module: http://hugin.sourceforge.net/tutorials/Mosaic-mode/en.shtml

You probably have two options for moving the camera.

Rotating the camera using a panorama head (E) Or moving the camera as I mentioned early. (F) I think this would depend on the space you have. If you have plenty of distance to the painting, you could probably be ok only rotating the camera.

Take a look at this regarding the panorama head: Do I "need" a panoramic head to shoot 360 panoramas?

V. Color, quality

I would recommend that you hire a professional photographer. Color is not something easy to match. You need to take exposure readings, use color targets, calibrate your workflow, color profiling, eliminate vignetting, etc.

You probably will not eliminate the glare, but control it. In some paintings, glare gives texture to the painting. You probably want to have also shadows, depending on how textured your art is.

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To automate it, you would need a robotic arm to reproduce your camera positions.