My Grandfather’s Data

Edward — Mon, 17 Aug 2009 15:17:00 +0000

The urge to preserve the recorded artefacts from our ancestors is basic – the stories we tell to keep their memories alive are so much more vibrant, and more easily recalled and re-told when they’re anchored to a photo, a video or a letter. But how do we collect and preserve all that data: the photos, the letters, the videos, the documents and emails? My father’s father left behind precious little in the way of recorded information – to my knowledge there’s a handful of photos and a letter he wrote to my uncle, which I’ve seen but not read. No doubt there is more, but not substantially so. It’s a simple decision for those who possess these artefacts to preserve them all, to the greatest degree practical. No need to organise and catalogue the contents – there is just so little there to preserve. But things are changing.
The physical record of my father is already far richer in content. He has lived through an age when high-quality colour photography became widely available and affordable, first in the form of 35mm film, then in digital photography. He’s been writing documents and mail (paper and, later, electronic) on a PC since purchasing a computer (an Intel 80286 based machine with a whopping 1MB of RAM) around two decades ago as a mature-age university student. We’ve never been the sort of family to make home-movies, but with phones and stills-cameras now offering video recording as standard, the temptation to flick over from stills to video every so-often is becoming irresistible. Even so, thus far the sum of all this information might amount to a only shelf full of photo-albums, a few binders full of documents, and literally a few minutes of video.
Skip forward now to the generation that will call me grandfather (hypothetical, since I have no children of my own at this point). As a third child, whose parents had grown tired of photographing children and their antics, my own early childhood shall retain some level of dignified mystery. However, as point-and-shoot film cameras gained popularity my life, at-least the part of it I spend at family gatherings, has been subject to far greater scrutiny. Now, between my family’s photos of me and my own photos of the things in my life, there are literally thousands of images that I’ll be leaving behind for my grandchildren to sort through. I’ve done them the favour of scanning the 1424 frames of my own films that were remotely worth looking at, but I fear it will be small consolation when they find the 8724 photos I’ve taken on my first DSLR since purchasing it just three years ago, or the tens of thousands more that I intend collect over the next several decades. I still have most of the personal emails I’ve sent and received in the course of my adult life. It is no slight upon this hypothetical generation when I suggest that the probably won’t bother reading even the tiniest fraction of them: I can’t imagine anything much more boring than reading through the minutiæ of someone’s electronic correspondence.
This is not the part where I start to rant about the folly of all this vast collection of data and preach a return to “simpler times” when people only recorded the things that “really mattered”. Actually I think it’s all rather wonderful, and I envy my grandchildren the high-definition, wide-screen, surround sound view that they will have into what will no-doubt be regarded as the quaint, old-fashioned times in which we live. I have just two questions:

What plans, if any, do you have for collecting preserving the data left behind by your grandparents, or parents?
What plans, if any, do you have for curating your own data to present it in the most accessible way for your grandchildren. Will you be leaving behind an unsorted blob of information, or picking out the most interesting parts for easy access? Will you delete all the saucy bits, leave them stand, or lock them in some kind of data time-capsule, to be opened only after all your children have died, to save them the embarrassment?

In answer to the first, since I can produce passable scans of both film and prints, I think perhaps I should take it upon myself to collect the few photos that exist of my grandfather. The second is far more difficult – I expect the most I can hope to manage is to keep the record in a single, largely unsorted, uncatalogued blob. I can’t imagine wishing to censor anything. In-fact, I intend to be the kind of old man that drops the most inappropriate details of youthful follies into casual conversation. You have been warned.

Enhancing highlight-areas in digital photos

Edward — Mon, 30 Mar 2009 02:16:17 +0000

This is a technique I use to eliminate the colour-banding that often occurs around highlights in digital photos. It requires that you are shooting RAW files, rather than JPEGs. The images below all link to larger versions, so if you’ve no idea what I’m talking about, just open the first and last images in different browser windows/tabs and flip back and forth between them to see the effect of the technique described below.

The Problem

The screenshot below shows a detail from a photo with no adjustments applied:

Base image

There is unnatural banding of oranges and yellows around the highlights on the arms and hands, and on the top of the cake and the dessert in the foreground. This banding is caused by channel-clipping, skip to the next heading for the solution or read on for the in-depth explanation of the problem:

In the white highlights, the red, green and blue channels are clipped at full intensity. In reality the candle-flames were orange-ish yellow, not white, but since we’re dealing with a much nore limited dynamic range it makes sense to render (comparatively) very bright objects as white.
On surfaces a little further out from the candles, the intensity of the blue channel starts to drop away. The red and green are still more intense than we can display within our limited dynamic range, so they’re still clipped to full intensity. With the blue channel dropping away, everything starts to turn yellow.
A little further out, the green channel starts to drop away but the red level is still brighter than we can handle. With the blue mostly gone and the green heading downhill we get a big slab of orange.
Eventually we reach surfaces so far from the flame that the red channel starts dropping within our displayable range, and at that point the colour is back in balance.

The Solution

It turns out that digital camera sensors capture a much greater dynamic range than we usually see in the final image, the conversion software takes a slice of that range and maps it to the final pixel values. That means that even when the red channel is clipped for a particular pixel, the raw data from the sensor may not be clipped at all. So, how do we get to see all that unclipped data? Simple, just use negative exposure compensation (turn on the overexposure indicator then decrease exposure until there are no areas indicated):

Darkened image

We can see the missing detail now, but everything else has gone dark. The important thing is that only the very brightest subjects the sensor recorded are now mapped to the maximum channel values in the final image. We can’t push the exposure compensation back up to lighten the image, that only gets us back where we started, so we need to use the base curve:

Fixed, but with low contrast

This curve leaves the white-point alone (it still touches the top-right corner of the grid) so it’s still mapping only the sensor’s brightest values to the maximum channel values in the output (I’ve turned overexposure indication on, so you can see that only the centres of the flames are overexposed), but it lightens everything in-between, bringing it back up to around the level of the original image. Cramming in that extra bit of dynamic-range tends to reduce contrast a small amount in other areas of the image, I find that putting a slight concave in the first segment of the above curve helps to compensate:

Final image, with contrast restored

You’ll need to tweak the other control points to maintain the overall brightness and ensure the curve touches at the top-right corner as I have above, then you’re done. The banding is gone, instead there are smooth transitions from highlights to normal exposure. One side effect is an apparent lightening and desaturation of the highlight areas (in particular compare the dessert at the bottom of the frame) – it’s not a bad thing, in fact it usually looks vastly better, but it’s worth being aware of.

I’ve used UFRaw for this demonstration, but the same techniques should work for just about any RAW converter. In-fact I’m sure some converters are already offering built-in functionality similar to this, or will do before long.

Edward Coffey's Blog » photography

My Grandfather’s Data

Enhancing highlight-areas in digital photos

The Problem

The Solution