marcoso - Ah, of course! I will include the script at the bottom of this post (It is 99% accurate to my spoken narration in the video).
mik1190 - Yes, I initially thought PhotoScan would automatically increase contrast itself, but now I don’t think this is the case. I’ve noticed a dramatic increase in point cloud quality when using very contrasty source images. I know what you mean about all the time and work required! The last thing you want to do is invest so much time only to find you didn’t shoot enough photos in the first place. Sometimes what I will do on complex scans is shoot “preliminary” images and process without any masks, just to see where the problem areas will be. Then when I go back to shoot my true photos, I feel more confident that I’m not overlooking anything, which is very easy to do!
Maybe one day I will revisit the sea shell to capture both sides!
ivaydesign - Thank you! I’m very glad you enjoyed it!
TheAlmightyF - That is very encouraging to hear, thank you! Even though my channel isn’t really a tutorial channel, I really wanted to do a good job on these videos. It’s my hope that they remain quick, informative, and not too boring to watch. It’s great to hear that you enjoyed it!
Here is the script for anyone who would like it:
Good day, and welcome back. In our last video, we covered the basics of shooting images for PhotoScan. In this installment, things get a little more advanced as we begin using turntables and masking our images.
Using a turntable means that instead of moving the camera around the subject, the camera remains stationary and the subject rotates. In my opinion, this is the most effective way to scan, because it eliminates motion blur even when using a very slow shutter.
I bought my turntable on Amazon from a company called LapWorks. It’s 16" in diameter and can support 200 pounds. However, if your object is light enough, a standard kitchen turntable, or Lazy Susan, is more than adequate. You may even already have one in your kitchen or refrigerator. In fact, if you’re scanning something small, I would recommend using a smaller turntable, as it will allow you to place your camera closer to the object.
Lighting for turntables- Whether you choose to use natural, ambient light outside, or artificial lights inside, it is vitally important that the lighting is extremely flat. From the camera’s point of view, there should be no evident light source, and no shadows. Otherwise, you can end up with very strange looking errors when PhotoScan attempts to align your images.
In this video, I’m using CFL softboxes from Ebay, but you can also try using a light tent, or even just good, old-fashioned shade.
Okay, we have our turntable and our lights, let’s shoot something!
I’ve marked off 10 degree increments on my turntable, and put up a solid background, so that PhotoScan doesn’t pick up any points besides the subject - for this example, I don’t want to worry about masking.
Starting simple, we’ll begin with the Default Rock. Stick it on a stand so we can shoot high, mid and low angles. I’m also using a cabled shutter trigger to eliminate motion blur. To save time, I’m only shooting half the rock.
In a few minutes, I have three rows of 18 photos each. Before bringing these images into PhotoScan, I’ll use Adobe Camera Raw to make adjustments. I’ll create two versions of each image- one set will have the Contrast pushed way up, as far as I can go without clipping my highlights or crushing my shadows. The other set will be the opposite, setting contrast to 0. Also be sure that your white balance is the same across all images. I like using Bridge and Camera Raw because it’s very quick and easy to make changes to multiple images at once.
Now we’ll open PhotoScan. Open the high-contrast images and align them. Even with just the sparse point cloud generated, we already have a decent looking result. If your scan already looks like what it’s supposed to be at this stage, you’re gonna have a good time.
After further processing and mesh generation at medium quality, we get this result. Even with only half the rock scanned, and no masking at all, we have a pretty good recreation. By replacing our high-contrast images with the second, neutral set we made, we can create a natural looking texture map for the model. Here is our final result.
So- moving on. Say you want to scan something more complicated than a rock. Masking can help. I’d rather gouge my eyes out with corn holders than to mask images by hand, so we’ll want to automate the process. There are two ways to do this- the first is to set up a chromakey background, and generate your masks in an external program. I’m using Keylight in After Effects to do this. When you export your black and white masks, be sure to give them the {filename }_mask suffix. For example, IMG_1234.jpg would have a corresponding mask image called IMG_1234_mask.png.
The second option is to use the “from background” method. This works by comparing your source image to another image, where the subject has been removed and only your background is photographed. PhotoScan compares the images to determine what is different, and generates a mask to ignore what it believes is the background. Because we’re shooting on a turntable, and the camera is locked down, we can use the same blank background image many shots. You only need to shoot another background image when you move the position of the camera. Fiddling with the tolerance may be necessary- for the shots of this soldier, I had the tolerance set to 6.
Both methods allow you to mask a large set of images quickly.
What if you want to scan something very small? Here is a sea shell, approximately 2" in diameter. To begin, I switch to a smaller turntable, and place the shell on a stand with a bit of poster tack to keep it from moving. Then I use a diopter on my 50mm lens to allow the camera to focus much closer. I’m shooting at f/22 to increase my depth of field.
Again, I’m quickly shooting just three rows of images, without any masking. In the final result, you can see that we’ve captured much of the detail in the shell. It is possible to capture even smaller objects- it all depends on your camera gear and the number of images you shoot.
Now let’s take everything we’ve learned, and combine it into a single scan. We’ll be using the Advanced Rock for this. First, put it on a stand so we can get upper, mid and lower angles. I’ve hot glued the rock onto the stand. Next, we’ll shoot our source images against the chromakey background. Because our screen isn’t big enough for all our shots, we’ll also shoot a background image for the high angles. This means our masks will be generated using a combination of green screen keying and the “from background” method. After processing our image sets, creating the masks, aligning the images and generating the final mesh and texture, we have it- a 20,000,000 vertice mesh that’s ready to cripple your framerate.
There you have it, the basics of shooting objects on a turntable. A big thank you to Wishgranter for generating the high quality sea shell and advanced rock meshes! You can find him over on the PhotoScan forums, which I recommend you visit anyway. There are a lot of helpful members there with many tips and tricks to share.
Our next guide will focus on shooting and generating environments with PhotoScan. So stay tuned, and I will see you in the next video!