Wednesday, March 4th 2015
Earlier today, I had received a call to the SilverTiger Pigeon Rescue Service. It seemed that, despite the netting installed to prevent such incursions, a pigeon had entered the small backyard at Tigger’s workplace and become trapped. No one seemed to know what to do about it – or perhaps they didn’t care – and, as I had already rescued trapped pigeons, I was asked to help. In the event, the match was postponed because, search as I might, I could find no trace of said Columba livia or rock dove. I conclude that it had somehow managed to find the hole in the net by which it had entered and thus escape. I might add that feral or street pigeons are a lot cleverer than people give them credit for. They are also excellent flyers and I have seen them perform exploits on the wing that took my breath away. Yes, OK, I love pigeons, but then, you already knew that
Despite the anticlimactic outcome, Tigger promised me a reward and so, on the way home, we stopped at the newly opened London Grind espresso bar on London Bridge. While drinking what is there called a “long black” and eating a cream horn, I thought about taking a photo or two. Not wishing to be too encumbered for pigeon hunting I had left my camera at home so had to use the camera of my iPhone instead.
I had an ulterior motive in taking these photos because I wanted to test further the stitching application that I wrote about in my last post (see Stitching photos to make a panorama). I took two sets of photos, one horizontal and one vertical. In the case of the latter, I was interested to know whether the software (Microsoft Research’s Image Composite Editor, commonly known as ICE) could cope with a vertical set of images or whether I would first have to rotate them and then rotate the finished photo back the other way.
Here is the horizontal set combined to make a panorama:
This stitched panorama is made of four separate images. These were taken from left to right consecutively without pause but even so they reveal movement. If you look closely you will see that two members of staff appear twice!
While making this composite, I also made a discovery about ICE. This works in stages and the third stage takes you to the crop screen. This, as its name suggests, provides the means to trim the photo, perhaps by cutting off any black edges. What I noticed this time, however, is that there is an option called “Auto complete”. What is this? Well, let’s give it a try and find out!
The result of trying it left me gasping. In a word, this option fills in all the blank bits left around the edges because of inequalities in the sizes and orientations of the photos. When it works, it is magnificent but when it doesn’t… but we’ll come to that in a moment.
For the London Grind photo it worked wonderfully well. What it does it to take bits from some photos and add them to other photos to fill in the blanks and complete the picture. In this case, it worked so well that it took my breath away.
Here is the vertical set combined to make a panorama:
This combines three separate images, taken from bottom to top. I did not have to rotate them for stitching as ICE was clever enough to see where the matching occurred. You will notice, however, that the stitching process has caused the edges of the window to appear curved. I don’t know the reason for this distortion and can only speculate that it results from the perspective characteristics of the individual photos.
This version of the photo has not been Auto completed. Why not? Well, because this is where the process sometimes falls down. In order to fill in a blank area, the application puts in it material copied from elsewhere and this may be inappropriate in that position. To give you a better example of how things can go wrong, I will combine the following three images which are admittedly quite unsuitable for forming a panorama.
Here is the result without Auto complete:
As you can see, there is a lot of black (unfilled) space around the edges of the photo owing to the incompatible shapes of the originals. If I had intended to take these photos for a composite, I would have framed them differently.
Here now is the result with Auto complete:
At first sight, this looks pretty good. It is at least a complete picture, nicely filling the whole rectangle. But then you realize that the top left and bottom left sections of the photo are pure fiction! They have been cobbled together from other parts of the photos, producing a sort of Frankenstein’s monster. It’s quite amusing, though, and depending on what you were trying to achieve you might in some circumstances find this version acceptable. It at least gives the illusion of completeness.
I may have had a wasted journey regarding the pigeon but I did have coffee and cake and make an interesting and useful discovery about stitching photos. I am well content with that!