How Many Megapixels?

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There are several cliches in the field of megapixel-count and resolution required for acceptable photographic prints.

In no particular order:

  • 300dpi is “fine art”
  • you don’t need as many dpi for larger prints because typically they’re viewed further away
  • my printer claims to do 360dpi or 1440dpi or …
  • 24 megapixels is more than enough for anything
  • “for a 5″ print you need 300-800pixels, for medium to large calendars 800-1600 pixels, for A4 900-1600px, for an A3 poster 1200 to 2000px, for an A2 poster 1500 to 2400px, …” (taken from a well-known photo-prints website guidelines)
  • it’s not about the megapixels it’s about the dynamic range

There are probably more set arguments in the field, but all are vague, arising from idle pontificating and anecdote over the last couple of centuries.

Here’s a key question: in a list of required image resolutions by print size, why does the number of dpi required drop-off with print size? What is the driving factor and might there be an upper bound on the number of megapixels required to make a print of any size?

We can flip this around and say that if prints are expected to be viewed at a distance related to their size, then it is no longer a matter of absolute measurements in various dimensions but rather about how much field of view they cover. This makes it not about the print at all, but about the human eye, its field of view and angular acuity – and the numbers are remarkably simple.

From wikipedia, the human eye’s field of view is 180-200 degrees horizontally by 135 degrees vertically (ie somewhere between 4:3 and 3:2 aspect-ratios).  Its angular acuity is between 0.02 to 0.03 deg.

If we simply divide these numbers we end up with a number of pixels that the eye could resolve.

At one end of the range,

 180*135 /0.03 / 0.03 / 1024 / 1024 = 25.75 (6000 x 4500)

and at the other:

200*135 / 0.02 / 0.02 / 1024 / 1024 = 64.37 (10,000 x 6750)

In the middle,

180*135 / 0.025 / 0.025 / 1024 / 1024 = 37.1 (7200 x  5400)

Significant points:

  • this is no longer about absolute print sizes; it’s simply about being able to view a print without one’s eye perceiving pixellation
  • the numbers correlate reassuringly with numbers of megapixels seen in real-world dSLR sensors today
  • you can reasonably say that if you have 64 Megapixels then you can make a print of any size from it
  • you can make an image with more than 64 megapixels if you want to, but the reasons for doing so are not directly to do with resolution – they might be
    in order that you can  crop it – either to physically crop the image in post-processing or to view it from a closer distance than that required merely to fill your eyes’ field of view
    or maybe for pixel-binning to reduce noise, give smoother tonality, etc
  • 24 megapixels is not enough for much; rather it’s is a turning-point: the bare minimum number of pixels for a person of limited acuity to resolve assuming they slightly less than fill their field of view with the print. 36MPel is more usable and 64 will keep you in business selling fine quality wall art.

Now we know how many megapixels are required for various real-world purposes, all that matters is making them good megapixels. Physics to the rescue.

 

Autumn at Glen Affric (2)

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Having visited my favoured spot overlooking the Caledonian Forest, I proceeded up the side of Am Meallan to the well-known location with a view over the lodge and along the length of Loch Affric.

It’s definitely an autumn morning location: the sun rises behind you, skimming up and over the tops of mountains beyond Loch Beinn a’Mheadhoinn, rising as it heads south; accordingly, patches of bright sunlight interspersed with cloud-shadows lap like waves across the undulating landscape from distance right over you.

Of course I had to make a timelapse video of it:

Loch Affric timelapse 2017-10-14 from Tim Haynes on Vimeo.

And two more photos to summarize the morning:

Sunlight and cloud shadow – an outcrop of Scots Pine and birch trees on Sgurr na Lapaich

Proper colours. The most beautiful shade of green pine foliage interspersed with orange/yellow warm birch trees, all lapping up the early morning light.

A classic view – soft heather and bracken leading past Loch Affric to the mountains beyond (Kintail / Glen Sheil in the very far distance).
I had befriended a fellow photographer down at the glen earlier; the first I knew that they had followed me a few minutes later up to this memorial viewpoint was the word “WOW!” exclaimed a few feet behind me.

Autumn at Glen Affric (1)

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For about 13 years I have been of the opinion that it has not been a year without at least one trip to Glen Affric.

My favoured time is autumn, late October, to catch the trees in the Caledonian Forest reserve at their most colourful.

Arriving before sunrise, the light is all dull  and the scenery a moody shade of gloomy – the last vestiges of moon stars remaining in the cobalt blue sky.

One of my favourite scenes at Glen Affric – two ncie birch trees amongst purple and green heather.
Sadly this shot has been marred in recent years by the installation of a large wide path cutting right through the heather between bench and trees; this photo used to be easier to compose but now I’m too conscious of having to position the frame to avoid the path just below; it’s becoming too much of a trick-shot for my liking.

 

Slowly, over the course of an hour after the posted sunrise time, the sun will gradually rise behind Meall Dubh beyond Loch Beinn a Mheadhoinn, casting a beautiful light on the forest:

Having arrived so early, it is a delight to bask in the first proper warm sunlight of the day:

One of my favourite birches – always think it should be called “Dancer” for some reason – basking in the first warm rays of sunrise amongst the heather.

Sunrise at Kinnoull Hill

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Early one morning in August I set off up Kinnoull Hill in Perth; a 40-minute stroll through the woods and I arrived at the top just in time for sunrise.

There are a couple of classic viewpoints, although juggling foreground foliage is not the easiest. This is the view closer to the tower with a hint of sunlight behind the hill, a line of light streaking round to illuminate some of the yellow trees below:

Sunrise behind Kinnoull Hill, with the River Tay running along the Carse of Gowrie into the distance

And this is a little further back, the sun having risen illuminating the whole Carse of Gowrie and River Tay, sky still shades of yellow and pink:

A classic view of the tower and River Tay from Kinnoull Hill, Perth

Walking back through the woods was rather pleasant too – lots of dappled sunlight on the trees.

This was one of the first photo-sets I processed using Affinity Photo Pro on the iPad. Loving the colour and tone already!

Birnham Hill

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One of my favourite views is the Highland Boundary Fault running through the landscape, immediately in front of me standing at Stair Bridge Viewpoint part-way up Birnam Hill.

It looks particularly pleasant with light and cloud-shadows zipping over the trees too:

Photo-Walk 2017

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For several years, on and off, I’ve attended an annual Photo-Walk based in Inverary, Argyll. This year was no exception – always good to catch up with friends I’ve met on the walk previously.

As always, Argyll is a favoured place and Autumn a favoured season; the combination of light and landscape makes for enjoyable drives.

An auspicious viewpoint – right next to the public toilets on Inverary front – but it makes for a cracking view up the loch toward a spot of sunlight illuminating the hills around Ardkinglas.

This time the organizer, Richard, had brought a couple of props – most notably a bottle of Isle of Jura Superstition and I had one or two ideas in mind “just in case” we ended up at a particular favourite waterfall.

 

We made our way down the slippery embankment to the burn, where I set up tripod amongst the boulders to maximize the lead-in lines of water flowing around the rocks up to the waterfall – tripod placement was fairly tricky with a wide-angle (24mm) lens and the slippery lumpy terrain to negotiate – and then as the camera was busy taking 20s exposures (4x with pixel-shift) I trotted back and forth through the water firing a flash-gun down onto the bottle of whisky and surrounding rocks (manual triggering at 1/8 power with the diffuser out and reflector down to stop the light itself registering in the scene).

Product Placement
I quite like Isle of Jura whisky… not necessarily on the rocks though.

I had originally experimented focussing in on the bottle itself and using a wide aperture to restrict depth of field, but that did not fall naturally through the scene – the waterfall was still sharp behind – so I stopped-down to make everything in focus and relied on post-processing tricks in Affinity Photo to draw the eye onto the bottle differently instead – some Orton effect and various soft-light Gaussian blurs, masks and elliptical gradient fills to boost the saturation, make it all glow and still leave the bottle sharp and bright. The final toning came from Snapseed of all things.

I’ve done a little product-photography before but never tried blending [bad pun intended] it with landscape work, let alone pairing it with light-painting, but I think it worked – certainly compared to the straight shot, the bottle with its amber glow just makes it.

Morvern 5/4: The Road Back

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And so we come to the last post in the series, a set of photos not entirely in Morvern but more on the way back up the shores of Loch Sunart and Loch Linnhe to the Corran Ferry, across and down to Loch Leven at Ballachulish.

There’s something wonderfully uplifting about rattling along these wee roads on beautiful sunny days, admiring the light.

Morvern 4/4: The Viewpoint

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After the long drive, the walk in the woods, the angst of the cleared township, the second part of the walk resumes through the woodlands up hill to the viewpoint, looking out over Loch Doire nam Mart to the caves in craggy Beinn Uamh and beyond. On a sunny day with a few white clouds in a crystal-clear blue sky, it doesn’t get much nicer than this.

After a second walk through the woods around Aoineadh Mor, towards the top of the hill one comes across this beautiful view: conifer trees, Loch Doire nam Mart and more trees scattered on the slopes of craggy Beinn Uamh, all beneath a crystal clear blue sky.

Well, it does get a little better – Doglet had his dinner on the shores of the loch in amongst the rushes. Lucky chap.

Morvern 3/4: In Search of Purity

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Time to explain the motivation for this excursion to the Morvern peninsula.

A few months ago, I was exploring what Google Earth had to show for the West coast of Scotland. A lot of photographers gravitate toward the north-west, around Sutherland, and rightly so – the geography up there is impressive. However, coming a little south past Ardnamurchan, there is also epic geology – evidence of volcanoes, beautiful mountains, the works. And so I stumbled across this glen past Loch Arienas and Loch Doire nam Mart, thinking there might be a view to enjoy part-way along the glen up one of the mountains to the left, perhaps.

On a little research, I saw the OS map of the area showed Aoineadh Mor, a former township dissolved in the Highland Clearances. Interesting history. So I drove – about 4.5 hours from Perthshire out through Fort William around Loch Eil and down at some length on wiggly single-lane 60-limit roads – and arrived at the small roadside carpark about 4.30pm.

The walk through the woods was beautiful: birches and oak trees catching the low sunlight.

Now it gets real. On emerging from the woods, the first evidence of habitation one sees is this broken dry-stone wall:

The Perimeter is Breached

which shouts the beginning of the story loud and clear: a township left to ruin, increasingly taken over by nature.

From what I gather, up to the 18th Century, Aoineadh Mor [approximately pronounced, and sometimes spelled, Inniemore, although the Gaelic ao vowel sound is inimitable in English] was a thriving crofting community on the slopes of Sithean na Raplaich where the burn (Allt Aoineadh Mor) flows down to the lochs.

It is a wonderfully beautiful setting – the Allt Aoineadh Mor burn burbling down the hillside, through the former township of the same name.

In 1824, Christina Stewart, newly owner of the Glenmorvern estate, forcibly ejected the crofters in order to farm sheep on the land for supposed greater profit, as happened in many places during the Highland Clearances.

The names of two of the last crofters to leave, James and Mary, have been given to two paths through the surrounding forestry.

By 1930 the sheep were also no longer profitable and the area was planted with trees as the cash-crop of the time. After 60 years, in 1994, the Forestry Commission uncovered the township.

And so my history intersects with the place in 2017.
It is both quieting and disquieting simultaneously: quiet in that there is an open space, there are trees, light, water, all the elements of landscape we photographers like; yet disquieting in that the area is not really pure – on scratching beneath the surface, there seems to be a greater innocence in the subsistence existence of crofting, with subsequent industries of sheep farming and forestry tainted by crass desire for profit to varying extent. And so the hillside is not really wild but barren; the land not just beautiful but exploited.

Dust kicked-up by a passing logging lorry travelling a path through Forestry Commission conifer woods, taken from the former township of Aoineadh Mor.
http://scotland.forestry.gov.uk/activities/heritage/historic-townships/aoineadh-mor-inniemore/marys-story

These conflicting forces of land, money and habitation are summarized in this photo, where we have nature’s pine tree felled in the foreground, a generation of mankind’s ruined croft superseded by the unnatural choice of conifers blown in as seed on the wind, leading to blue skies beyond.

This used to be the township of Aoineadh Mor, a scattering of stone crofts on the braes beside a beautiful river surrounded by forest. 
Now the Forestry Commission has taken over, with several monoculture forests on the surrounding mountains, even wild-seeding into the former township.

For what it’s worth, a few more photos all taken around the township:

References:

As I walk along these shores
I am the history within
As I climb the mountainside
Breaking Eden again – Runrig, Proterra

Morvern 1/4: Approach

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The West coast of Scotland – Lochaber, Argyll and further north – is well known for its amazing scenery. Earlier in the year I had a look around on Google Earth and thought the landscape looked pretty impressive opposite Mull around the Ardtornish area on the Morvern peninsula.

It certainly did not disappoint. Even having just driven 4 hours all around Fort William, across and round Loch Eil at great length (single-track road with passing places and a 60 limit), I had to stop to admire the crystal clear blue sky and lines of mountains receding into the distance:

There followed a short drive down to Loch Arienas, which was also just beautiful – blue water reflecting blue sky:

Lady Mary’s Walk, Crieff

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Only catching up on photos taken at the end of April…

Lady Mary’s Walk runs West from Crieff along the side of the River Earn, mostly on the flat until one reaches the foot of Laggan Hill after a mile or so, where it forms a circular route back to MacRosty Park.

At the end of April I went for a stroll to hunt bluebells.

The path was particularly pleasant – quiet, leading on through the woods.

 
 
 

As an aside, I’m sure there never used to be such a profusion of wild garlic on these Perthshire woodland nature trails 10 years ago – I only first encountered the stuff whilst out in Galloway.

I was a bit early for optimum bluebell season, but did find a few areas of good blue ground coverage:

And at the western extremity of the route there is a ruined house – it could be quite eerie given the right lighting.

The Return of Serif

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It feels funny to think that back in the early 1990s Serif was known for PagePlus, in the days when such things were known as desktop publishing or DTP applications.

Recently, however, they’ve produced Affinity Photo for Mac, Windows and iPad. After one or two folks recommended it, I thought it was time to add another trick to the photo-publishing workflow and have a play. After all, if nothing else, having an iPad would solve my doubts with colour-management issues on Linux, wouldn’t it?

So I’ve spent a few weeks driving around hunting scenery and taking photos of it and gradually evolving a few routines: photos are still shot on the Pentax K-1; processed (variously pixel-shift or HDR) using dcraw on Linux, where I also run them through darktable for a lot of toning work; the results are then copied to an ownCloud folder which synchronizes automagically with the iPad; a bit of juggling with share-to-Affinity and share-to-Photos and share-to-ownCloud later and the results are copied back to the workstation for final organization, checks and publication.

Within Affinity, my workflow is to import an image and ensure it’s converted to 16-bit P3 colour-space – this is a bit wider than sRGB and native to the iPad’s display. I then run the Develop module which tweaks exposure, brightness and contrast, clarity, detail, colour-balance (not so much), lens distortions, etc. After that, I use layers to remove sensor-dust and other undesirable feature. Top tip, use a new pixel layer for the in-painting tool set to “this layer and below”; then all the in-paintings can be toggled on and off to see the effect; also use a brightness+contrast adjustment layer above that while you work, so the corrections will be even less visible when the contrast is reduced back to normal. If the image requires it, I’ll add one or two fill layers for gradients – better to use an elliptical gradient that can be moved around the scene than a vignette that only applies in the corners. Finally, I merge all the layers to a visible sum-of-all-below pixel layer,on which I run the Tonemapping persona; ignoring all the standard presets (which are awful), I have a couple of my own that make black-and-white in low- and high-key targets, in which I can balance local versus global contrast. If I produce a black&white image, it probably arises from this layer directly; sometimes, dropping the post-tonemapped layer into the luminosity channel makes for a better colour image as well (subject to opacity tweaking).

So, some results. It produces colour:

It produces black and white:

One final thing: I used to hate the process of adding metadata – titles and descriptions, slogging through all my tags for the most pertinent ones, etc. Because the ownCloud layer is so slow and clunky, it makes more sense to be more selective, choose fewer photos to go through it; if I also add metadata at this stage, I can concentrate on processing each image with particular goals in mind, knowing that all future versions will be annotated correctly in advance. Freedom!

Along the Oak Walk

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One of my favourite walks around the local area is the Oak Walk – running along the edge of a large field, it gets beautiful evening sunlight and has some characterful trees

One or two local folk have populated it with wooden sculptures, for amusement factor

And the surrounding paths are well populated with wild raspberries, brambles and even willowherb/fireherb looking pretty in the light.

Trying something a little different

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For years now, my photo-processing workflow has been 100% open-source. However, in the interests of greater portability – hack on photos whilst on the go – and partly gratuitously for the sake of variety, I recently acquired an iPad Pro 10.5″ and installed the Affinity Photo app.

As a user experience goes, it’s really quite pleasant. The best way to synchronise files around the LAN seems to be Seafile, which is open-source and available for Linux, iOS and android. My Linux-based workflow regularly produces 64-megapixel images, working on multiple intermediate TIFF files, 16-bit ProPhotoRGB-linear; somewhat surprisingly, seafile, the iPad and Affinity Photo seem able to handle files around 450MiB in size. There are a few small gotchas – I had to import a few ICC colour profiles by hand and as yet, there doesn’t seem to be a way to customise export options (so you have to select JPEG 99% sRGB lanczos yourself afresh every time); I’m sure these things will come in time however.

So here’s a shot from last Sunday afternoon. As I was heading out of Muthill I saw this characterful old tree in a field; on the return journey a few hours later, not only was it still there but the clouds were darker in the background and the golden sunlight caught the bare branches. A very quick bit of parking and even quicker sprint back to the optimum viewpoint and it looked stunning. So I processed it a little further, realising an intention for how it should look that was apparent from the start.

Sunlit tree