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This course is a collection of short Photoshop and Illustrator projects and creative effects that can be completed in ten minutes or less. The series is taught by computer graphics guru Deke McClelland, and presented in his signature step-by-step style. The intent is to reveal how various Photoshop and Illustrator features can be combined and leveraged in real-world examples so that they can be applied to creative projects right away.
- Hey, gang. This is Deke McClellan. Welcome to Deke's Techniques. This week, I'm going to introduce you to a few medical imaging functions inside Photoshop, which means if you're working with Photoshop CS6 or earlier, you'll need the extended version of the program. If you're using Photoshop CC, then any version will do. Specifically, I'm going to show you how to take a bunch of MRI scans, that is magnetic resonance imaging scans, and combine them into a single 3D object inside Photoshop. Even more specifically, we're going to take a look at my knee.
The idea is I was playing volleyball with a bunch of folks that were younger than me, which is always a bad idea, and I was going for the ball and I just smashed my knee into the dirt. The good news is I made it. I did get the ball in the air and we ended up getting a point, but the bad news, of course, is that I played for another two hours because I didn't want to look like a wimp. For a while there, my knee was in bad shape. It's all better now, but we didn't know what was going on. I went to a specialist and he did a bunch of MRI scans. If you don't know what these things are, they're essentially a bunch of cross sections, like x-rays almost.
then they gave me a DVD of all these things and then I opened them up and combined them into a 3D object inside Photoshop. You can do this very thing with your own medical images as well. Here's a representative slice. In case you don't know what you're looking at, I went ahead and color coded it. We have the muscle. These incredible powerful leg muscles over here on the, what is this, the right hand side. Then we've got the bones, which are the femur and the tibia down the center, separated by a little bit of meniscus. Then over here on this side, we have the patella, better known as the knee cap.
Now, these things don't really appear in color. They appear in black and white and there's a bunch of them. What we're going to do is combine them into a single 3D object, which I've color coded yellow just for the heck of it. Then you can spin it around and look at it as intensely as you like. Here, let me show you exactly how it works. Here's that final 3D rendering of my knee based on the MRI data. The first thing we need to do is load up all the DICOM files as independent layers. You do that, here inside the most recent version of Photoshop, by going up to the file menu, choosing scripts, and then you choose load multiple DICOM files.
Then, if you're working along with me, go ahead and navigate to this DICOM file sub folder and then go ahead and click okay. A moment later, you'll see a bunch of these MRI slices represented as independent layers here inside the layers panel. If you want to view those layers for whatever reason, you may or may not where my knee is concerned, but if you have your own DICOM files, you might find this very interesting. You want to alt click or option click on the eye in front of the top selected layer. Make sure that it's selected and that way, you have just one layer active and you're seeing that one layer independently of the other ones.
Then, with that layer selected, press alt left bracket. That's going to be option left bracket on the Mac. By left bracket, I mean that square bracket key that's just to the right of the P, as in Paul, key on an American keyboard. Notice as you do, you're going to skip from one layer to the other and you're also going to make the new layer visible so that you can see each one of those slices like so. Now what you want to do is select all the layers and change their order because we're seeing them in reverse order at the moment.
To do that, just go ahead and alt click or option click on the one eyeball that we were seeing a moment ago so that we're seeing all the layers. Then press control alt A, or command option A on the Mac, to select all of the layers here inside the layers panel. Then, you want to go up to the layer menu, choose arrange, like so, and then choose this final command, reverse. That'll swap the order of all these layers. Now we want to combine them into a 3D volume. You do that by going up to the 3D menu, choosing new mesh for layer and choosing volume.
Again, this is how we do things here inside of Photoshop CC. If you're using a different version of the software, you're going to find this command in a different location. After which point, you'll see this dialog box here asking you for some scale values. Don't worry about them. Just go ahead and click okay in order to create the 3D volume like so. Presumably, Photoshop is going to automatically switch you to the move tool up here at the top of the toolbox. If you look up here in the options bar, the 3D mode should be set to this very first guy, which is the orbit tool.
At which point you can go ahead and drag the 3D rendering like so. If you're looking at the front of the leg, you'll get a pretty good view of what's going on. If you drag around to the side, you're going to see all of those slices. Those are those independent DICOM files that we had on separate layers just a moment ago. I'm going to go ahead and drag this guy back around like so. I believe this is the front of the knee that we're looking at at this point. Most likely, you're not going to want to see all of these source images represented as a diffused texture.
That is to say, we're actually wrapping those images around the surface, which is not necessarily what we want. In which case, just go ahead and turn off that eye below the word diffuse. Then, go up to this pop up menu in the upper right hand corner of the screen, which allows you to switch work spaces. Then go ahead and select 3D so that you're looking at the 3D and properties panels. You should know that these kind of medical 3D volumes are a special breed of 3D object inside of Photoshop.
Even though we've got this render button right here, it's not available. Notice that I'm seeing the little Ghost Busters cursor, which is telling me that I can't ray trace this object. I also have no option for modifying the material by the way, but we can style the object up here in the properties panel. For example, I could switch the volume metric style from the default here, maximum intensity, to transfer function, which is going to allow me to apply a gradient map that I can use to color the object.
First it's not going to look very good, which is why I'm going to take this opacity scale value all the way up to its maximum, which is 10. You want to make sure that enhanced boundaries is turned on. Then, go ahead and click on the gradient bar in order to bring up the gradient editor dialog box. I'm just going to get rid of this black stop, like so. In Photoshop CC, you can make a gradient with just one color, as you're seeing here. Then, I'm going to double click on that white color stop and I'm going to dial in a shade of yellow instead.
You can go your own way, of course, but I'm going to change the hue value to 55 degrees and I'll bring the saturation value up to 100 percent like so. Then I'll click okay. Now I want the darker stuff in the knee to be transparent. I'm going to click on this first opacity stop right here and I'm going to change the opacity value to zero percent like so. Then I'm going to drag this diamond, which is the midpoint skew for the opacity all the way down to a location of 15 percent. In other words, I'm dragging it quite far over here to the left in order to produce this affect here.
Then I'll go ahead and click okay to apply that transfer function. You may see a little bit of a switch on screen, incidentally. At this point, you could go ahead and drag the knee around some more if you feel like you want a better view of things. In my case, for example, I can see the femur up here at the top of the leg and I can see the tibia and the fibia bones down below. You also have the option of seeing some anatomical cross sections. You do that by turning on this cross section check box. What I recommend you do, at least where this particular object is concerned is change the slice to garad right there.
I'm also going to take the opacity value down to 30 percent, which ironically makes things more opaque on screen. Now notice that you have the option of digging into the knee, here, by reducing the offset value. Notice I'm going all the way to the back of the leg when I reduce the value to negative 100 or I can increase the value to C forward cross sections. I'm going to make things a little more obvious here by turning off this pling check box.
That kind of lights up the knee a little bit and I'm also going to turn on the intersection check box, which will make for a little more contrast. You can select different sides if you want to if you want to experiment with that. You can even swap the cross section sides. For example, if I swap these sides with a high cross side value and then I decrease the off set value like so, I'm going to see some of those forward slices from the MRI. All right, friends, I think that's about it. That is, after all, how you take a bunch of MRI slices saved out as DICOM files and you assemble them into a gruesomely detailed 3D volumetric object here inside Photoshop.
Gosh, wasn't that a special treat? I thought about calling it Deke's Knee in 3D, but I was pretty sure nobody would watch that. If you're waiting for next week's technique, I'm going to show you how to assign multiple strokes to gradient type inside Illustrator. Notice that we're filling in the holes between the letters. Deke's Teqniques, each and every week. Keep watching.
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