4×5 Digital Back Part V – High Resolution Color

UPDATE 8/29/16: I see that OpenSeadragon is linking here.  LATEST Openseadragon images are here on Tumblr. (Thanks again Ian Gilman for making that possible!)

For now, I’ve put aside my goal of high-speed image tiling for portraits.  Instead, I’m trying to get a reliable (manual shooting) work-flow for 4×5 imaging for landscapes or still-life photography.   The servos and gears I’ve acquired will have to wait.

You may wonder why I’m bothering with this project when I could buy a Rhinocam.  There are many reasons, but one is that the Rhinocam takes 6-8 shots for a 58mm by 48mm composite, a little larger than medium format.  I current do 42 overlapping images for a 127mm by 100mm composite, or true 4×5.

I’ve noticed that even in the best light, I can’t access the full 12-stops worth of dynamic range from today’s digital cameras (ISO 100 say) without resorting to risky camera-shake shutter speeds. In order to shoot at safe speeds of, say 1/250th, ISO I need to go above 3200. Stitching errors are common from imperfections in image orientation or lack of detail. For most applications, final 4×5 images do not look insanely sharper than a good DSLR/lens combination.  Developing the DigiTiler has been a struggle, starting with the difficulty of mounting it on a Graflok back.

All that said, I’m beginning to produce images with better color saturation. Large format cameras allow for more control in focus (tilt-shift) than is possible with DSLR setups–though I have yet to explore it. When I don’t get too many failures in the workflow, I can get images that I believe are impossible to get with any store-bought digital camera, even one costing $50,000.

Here are some examples. Here is a photo from a Sony A7 with Zeiss 55mm at f18 (to match the Graflex’s DOF at f32). I’m using an AlienBee 800 at full power, bounced off the ceiling.

Here’s a similar image created with the DigiTiler.  Nikkor 180 W at f32.  42-image stitch.

The Achilles heal of bayer sensors is they resolve more contrast detail than color detail.  I’ve gone into these issues here.

Now compare what the Digitiler can do.  First the native A7 shot:

Graflex with Digitiler

Here is a clear demonstration of bayer sensor color distortion.

Versus

Does this make a difference if you don’t crop the image or blow it up too large?  I think so, even at “retina” display resolution.  Certainly, twenty years from now, the quality of these images will be obvious on future higher quality displays.

Here is a portrait of my daughter that has nice color saturation.  She had to stay still for 30 seconds and got dust in her eyes so doesn’t look very happy.

Okay, the bad stuff…

Give Me More Light

I can take the Sony A7 with 55mm out and take a nice shot of a building at f4, ISO 100 and 1/60th. With the Digitiler I’m essentially taking telephoto shots (1.5 x 1 inch tiles) of a section of the building. With the Nikkor 180mm W lens set at f16, I need to shoot ISO 400 at 1/100th. However, because I’m effectively shooting long I can’t have any camera shake. To be safe, I’d really need to shoot above 1/250, in 4-digit ISO. In short, unless you use a flash and pump a ton of light onto your subject, you won’t be able to maximize your camera’s dynamic range; that is shoot at ISO 100. Large format film, of course, requires long exposures too. However, you only need to keep the camera still for one shot. Taking 42 still shots for a 4×5 image gives you 42 opportunities to screw up.

Stitching Software Is Fragile

In order for large format tiling photography to work, one needs stitching software. Anyone who does a panorama on their phone, or camera, probably believes that the computer world has made this process trivial. Unfortunately, when you’re trying to stitch together high quality images you quickly run into the limitations of today’s computers and stitching software. Since there is very little demand for the software, the technology doesn’t seem to have advanced much in the past 5 years (except again, for low-quality consumer stuff).

The best software for stitching that I’ve found for the DigiTiler is Microsoft’s Image Composition Editor (ICE). It’s free, but also seeming in-and-out of development. My experience is that there is no perfect stitching software. ICE does better with some images and worse at others. Photoshop also has its strengths and weaknesses. Then there’s panorama software, like Huggin or PTGui, which expects you to input lens parameters that I haven’t had the time to translate for what I’m doing.

Developing a software workflow for image processing and stitching is itself, almost a full-time effort.

In Progress

I’ve been using VIPS to create zoomable images out of my large format images.  Then using OpenSeadragon to display them on the web.  There doesn’t seem to be a one-stop easy application for non-techie photographers to post zoomable high-resolution images.  Even here, I’m able to post on a WordPress “page”, but not here in a post.  One of the many issues that bedevil me in this project.