Modern Software Experience

2009-07-06

photosynth in practice

Photosynth installer

The Photosynth Primer discusses what a photosynth is and how to view one. One thing it noted is that viewing has synths has become easier now that Microsoft is using a Silverlight-based Photosynth viewer.

I am happy that viewing a synth has become easier, but when I downloaded the Photosynth installer in early April, I did so to create a synth.

synther

The Photosynth installer contains the Photosynth creator, the application used to creator to make synths. This application is also known as the synther. You give it a stack of photos, and it creates a synth out of it.

system requirements

The Photosynth creator is only available for Windows.
You do not need anything out of the ordinary. You just need to be running Windows XP or later. If you are running Windows XP, it has to be have been updated to Windows XP Service Pack 2 or later. Smart people like you are of course already running with Service Pack 3, so this requirement should not be an issue.

photos

I’ve stuck with an old-fashioned SLR photo camera for more than twenty five years. For a long time, digital cameras offered too little and cost too much.

Thee quality / price ratio of digital cameras kept improving and the desire to play with Photosynth was one of the reasons that I finally bought a digital camera in April, and went out to take a few hundred pictures of the same thing.

simple

Using the synther to create a synth is very simple. You just download and install the program, create a project, add a bunch of photographs to the project, and then press the button. The rest is automatic. Photosynth analyses the photographs, makes a synth and finally uploads it all to the Photosynth web site, where others can view it.

patience

You do need to create a free account on the Photosynth site to do this. You also need a lot of patience while Photosynth analyses and uploads your photos.

That the analysis needs some time is understandable, but I found, just like many other people who tried this, that the uploading of photos to the Photosynth site takes longer than the synthing. Also, that it does not restart the upload smoothly.

first attempt

I had seen a few synths, but never made one, and had not bothered to read any manual or view any video on how to do it right.

For my first attempt, I selected a a local building. I made some 150 photos by walking around the object, taking pictures from various angles and zooming in on some points of interest. I tried to make sure there was some overlap.

empty

I actively avoided photographing any passing people. It is actually a popular place to sit and children love to climb its steps, so getting pictures without people in it was a bit of challenge.

87 % synthy

After throwing away some pictures that did have some passing people and cars in it, I created a project to make a synth. The synthing took perhaps half an hour, but the upload took about twelve hours!
Once it was done, Photosynth deemed my photo collection to be 87 % synthy, and the resulting synth was so-so; nice, but not fantastic.
I particularly noticed a few gaps between pictures, and pictures did that did not overlap well with any other picture.

second attempt

resolution

The Photosynth site offers a full screen view, but many users view synths on the web page, with a typical size of 400 by 300 pixels, and even at full screen resolution, using 10 megabit images is not necessary.

One thing that the first attempt made clear to me is that resolution is not very important, but having lots of images is. So I decided to have a second go at it with more but lower-resolution pictures.

Some details, such as small text on a poster, will be insufficiently recognisable at lower resolution. but that is easily solved by zooming in on any detail that is important enough to make an extra picture.

new batch

After seeing the results of the first attempt, I went out to make a new batch of images. I could simply have scaled down the existing ones, but I was also eager to get more overlap between the images. I ended up taking 444 images, and then threw away just 10 of them, because of passing cars or people in them.

discontinuities

I took all these photos in less than a two hour period. Even within that short timeframe, I encountered plenty of problems trying to get things right, and there are small discontinuities in the resulting synth. Ideally, nothing changes while you take your pictures, but as you walk take your pictures, everyone else does their thing.

I tried to make sure I had a good set of overlapping pictures by circling the object, snapping pictures as I did so. I then zoomed in on details of interest, made sure I had pictures of the pavement, the surroundings, and so on.
The results from the first attempt guided my second attempt.

People were passing by, opening and closing doors, opening a window and then leaving it open. Someone threw water out of a window, which made dark spots on the pavement where none were before. I did manage to convince one person to park their car elsewhere.

I avoided most discontinuities, but there still are some. There is man having coffee in some of the pictures. He was sitting peacefully, and did not seem to move at all, but he did get up and leave at some point. Another man came and picked up a blue bike that is visible in some pictures. So some pictures have the bike, others pictures do not have it.

SD Card

A digital camera has some internal memory, but the size of that memory is likely to be limited and may depend on a battery. You want a camera with an SD Card or something similar, so that you have plenty of room for a lot of pictures. Even at 4 MB per image, an SD Card of 16 GB will hold some four thousand photos. That is more than enough to make sure that you will hardly have to worry about the storage capacity.

batteries

One important tip is to use new or fully charged batteries and bring spares. A two-hour session snapping four hundred pictures was enough to fully drain the batteries in my camera.

first picture

You can select one of the pictures for Photosynth to use as the placeholder image for your synth, but I had noticed that it defaults to the first image in the set. So, this second time I went out, I deliberate photographed what I wanted to use as the placeholder image first.

portrait mode

If you don’t do anything about it, the camera thinks images are landscape mode, and I had been snapping pictures without bothering to set anything, so after downloading the pictures to my PC, I spent some time turning some of the images into portrait mode.
I do not believe Photosynth needs this at all, but I know that I do.

light

Various images with lots of sky in them were way too dark, and I corrected the light in those to show detail in the foreground objects. I did not bother trying to get all colours in all images exactly right. That might have taken days, and that would just not be worth it. The images need not be perfect, all that what matters is that they combine well for the desired 3D effect.

resizing

Together, the 434 remaining images took up more than 850 MB - and that was in JPG format.
The camera takes images in 3648 x 2736 (9.980.928 pixels). I decided to sample that down to one fourth, 912 x 684. That seemed a reasonable size to work with, and the resulting synth shows that it is plenty. After batch resizing the images, they took up only 70 MB.

synthing

I then feed those more than four hundred images to Photosynth. Photosynth warned me that processing more than 300 photos could take a lot of time, but I had resized them already, so let it move ahead anyway.

Photosynth makes very good use of the computer hardware. Photosynth used all four CPU cores, and the Window Vista CPU meter gadget showed all of them maxed out at 100 %, something I had not seen before.

Despite making very good use of the available hardware, Photosynth still took a lot of time synthing the pictures. It did not time it, but it was definitely more than an hour, perhaps two. Photosynth displays how synthy your photo collection as soon as it is done synthing. Photosynth rated my second attempt with 400+ photos as 94 % synthy. Judging by the examples on the Photosynth site, that is pretty good.

The decision to use many small files paid off with a much faster upload to the Photosynth site; just 2½ hours this time, and the result looked a lot better.

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