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Tutorial: Light Sources, Drop Shadows & Cast Shadows

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Take a look at this shop. I’ve seen this same problem asked about in numerous help threads thoughout the years.

Pope House the First

Pretty straightforward, simple headswap I knocked out in three minutes depicting that great religious leader Pope House The First. But something about it looks really “off”. I get this all the time, people can tell there’s something really wrong with it, but often can’t put their finger on what it is.

Here’s what it is.

Pope House the Second

With the problem outlined on Pope House The Second, it becomes glaringly obvious (lame pun intended). The shadows are hitting different sides of his head. It’s one of those things that even people who don’t Photoshop can usually tell is off, but couldn’t tell you why at gunpoint. Unless he has 5000 watt klieg lamps tight-beamed on opposite sides of his head, you’re NEVER going to see anything that looks like this in real life, so your eye starts telling your brain “Something’s not quite right here.”

Many, many sources are evenly lit, so you don’t really run into this problem. But if you DO see obvious shadows or light glare on an image, it’s imperative that you make the light look like it’s coming from the same direction on all layers. There are ways to sometimes “change” the direction that the light source appears to be coming from, primarily with the Dodge & Burn tools, but that’s a fairly advanced technique that I won’t get into at this time. My point right now is just to be cognizant of where the light appears to be coming from in your image.

Often times, the solution can be as simple as flipping one of the layers horizontally (Edit>>Transform>>Flip Horizontal).

Pope House the Third

There, Pope House The Third is more believable… but keep in mind, some people’s faces are surprisingly asymmetrical. If people are used to seeing someone with their hair parted on the left, or they have a prominent mole on one side of their face, you may find that flipping their face just lands you right back in “Something wrong, can’t put my finger on it” territory. In that case, you might consider flipping the body layer. As long as all the light appears to be coming from one direction, your eye doesn’t care which direction it comes from.

But there’s still a lighting issue. The light glare on House’s forehead is pretty intense, and unless the edge of that clamdigger hat is surgically implanted into his skull, there should be a ridge there where the hat meets his head that casts a small shadow.

Pope House the Fourth

There ya go. Took us until Pope House The Fourth, but the lighting issues are pretty well resolved now. (Never mind the crappy rez on the pope picture. Just wanted a harshly lit source pic to use here.) That last shadow is definitely what I would call a “nitpick”… but it’s exactly those kind of details that will make your shop look more natural.

Lighting issues don’t end with making sure that your source images show light coming from the same direction. In order to successfully trick the eye, you’re also going to need to add shadows to different layers in your composition quite often. Here’s an old entry of mine for the contest If Every Excuse Turned Out To Be True

Blind Refs

The original source, of course, is just the referees standing on the field, and likely taken very early in the morning, as they’re casting those long stretchy shadows (known as oblique shadows, if you’re interested…well, even if you’re not, that’s still what they’re called) . There are really only two ways to deal with a situation like this: Either clone out all the shadows and add your own, or make the shadows for the layers you’re adding match, in this case the dogs and the canes. I usually go for the second option, because the original shadows are obviously perfect for the rest of the lighting in the image. If you change how the shadows fall, then they may not match the rest of the image any more. In this case, look at how “blown out” the whites are on the right side of each referee… the light is pretty obviously coming from the direct right.

The primary tool supplied by Photoshop to add shadows, as most of you are probably aware, is the Drop Shadow function. It’s located at the bottom of your layer pallete, under the “fx” button.

fx menu

 This is a one-click solution, if you don’t change any of the defaults, but it leaves something to be desired. Let’s take a look:

Stickman With Default Drop Shadow

Okay, that does in fact provide a shadow. The main function of  a shadow, as far as our puny human eyes are concerned, is to provide information about depth. In the default case, it makes the stickman appear to be slightly above the surface he’s laying on. Let’s look at the options available to you :

Drop Shadow Dialogue

The first option you’ll see above says “Blend Mode” and has a black swatch next to it, with an opacity slider below. I could (and in fact, plan to) do an entire tutorial on blend modes, but just for the purposes of this tutorial, probably best to leave it on Multiply. Multiply tells it to to blend ONLY a dark layer cleanly with the layer you’re applying it to… So, since a shadow should generally be just a darker version of the color below it, this is exactly what we want. Yes, you can make your shadow any color you want. Lighter colors instead? You’ll want Screen mode, basically the opposite of Multiply. In fact, if you take a regular default drop shadow and change the color to white, leaving the Multiply mode in effect, you’ll see that the drop shadow completely disappears. As I said, Multiply is only good for darker colors.

That’s more detail than we need to get into for a simple shadow. Leave it on black and multiply.

The opacity slider, much as you might expect, changes the opacity of the shadow. Part of matching a shadow to a source image’s shadow is finding out just how dark it should be. Play with the opacity slider until it looks right to you.

Drop Shadow Dialogue

 The next section shows a circle with an angle marker and a tickbox for “Use Global Light”. You’ll generally want to keep Global light checked, as it ensures that all your drop shadows will fall at the same angle…change one, you change them all…but there may be times that you have shadows from multiple light sources. In that case, yeah, you might need to shut that off and set them individually.

You may change the angle either by dragging the angle marker in the circle around or by manually inputting the desired angle in the box next to it. I’ve seen some copies of Photoshop where the default was mysteriously changed to 30 degrees or some other setting. The “classic” default is 120 degrees, and the one I tend to use the most often if I’m making my own shadows and not matching a different source. Here’s the difference:

Drop Shadow Degrees Difference

 So, the shadow is falling in a different direction. If you’re following along with your own copy of Photoshop, you will immediately see why: The angle marker is pointing to a different place, meaning the light is supposed to be coming from that direction. So why is 120 degrees the “preferred” default? CUZ WE’RE AMERIKUN!


No, really. Kinda.

In goofy-Photoshop-land, it probably doesn’t make that big a difference. However, when you start working with text, any graphic design teacher worth their salt will tell you, as long as you’re dealing with English (or any of the other vast number of languages that read left-to-right), 120 degrees is what you want.

One of the basic concepts of art, and graphic design, is to draw the eye where YOU, the artist, wish it to go. If a drop shadow is set at 120, it matches the left-to-right, top-to-bottom action of the eye as it reads English. If you set it at 30, the eye is constantly being pulled in the OPPOSITE direction of the way you’re reading.

For this reason, I’m going to mention something farther down NOW. On the bottom part of that dialogue, there are two buttons: Make Default and Reset To Default. Reset To Default does just that, whatever your default might be. “Make Default” actually makes all your current settings the new default. So if your drop shadow is set to some funky number, you can change that by setting a new default here. And, while we’re here, “Layer Knocks Out Drop Shadow” basically just hides the drop shadow in places where it’s covered up by the layer content. Normally, this has no real effect, as the layer hides the drop shadow anyway, but it can come into play if you’re doing drop shadows on layers on which you’ve lowered the fill (made semi-transparent). That’s a pretty weird thing to do, so you’ll generally just leave this checked and forget about it.

Okay, back to where we were…

Drop Shadow Dialogue

 The next section is where you define the shape of your shadow, in order they are Distance, Spread and Size. Distance is how far away from the original layer to put the drop shadow. A larger figure will generally make the image look like it’s floating a farther distance above the background.

Distance Comparison

Here we begin to see some of the faults of a drop shadow: It doesn’t LOOK like a shadow we see often in nature. Most things you encounter in life aren’t simply hovering in the middle of the air like that.

The next two options work together, largely. Spread expands the area of shadow in general, as if the shadow is getting bigger due to distance from the background. Size expands the entire area encompassed by the shadow, but it doesn’t just make it bigger….it keeps the same amount of shadow and just extends the gradient out farther.

Spread Vs. Size

As with many options we’ll talk about in Photoshop, this is best understood by taking five minutes to play with the sliders now that you know what they’ll do.

Drop Shadow Dialogue

 The last section we haven’t discussed is quality. We have Contour, an anti-aliased tickbox, and Noise level. The contour refers to the shape of the shadow in three dimensions. Consider your layer as a plaque. The contour shape would be what the edge looks like from the side. The ones you’ll find in nature use a straight line like the default one shown above, but load up a few of those other shapes and look at what they do… probably not right for our current purposes, but you can get some interesting effects by using a different shape.

Anti-alias, as always, means you want Photoshop to try to make the transitions look as smooth as possible. In this case, though, whether you have it checked or not usually makes little difference… you have Size (above) to control how smooth you want the edge.

The last option is noise. This (wait for it) adds noise to your shadow, making it look “chunkier”, like static on a TV. Sometimes you’ll need to add noise to match, say, an existing movie poster. Many times it just makes the shadow look better if it’s on an uneven surface.

Better Shadows

So the drop shadow will work, and in some cases it’s exactly what you need. Anything that SHOULD appear to be floating absolutely NEEDS a drop shadow. But what about things that are, ya know… affected by gravity?

You need a cast shadow, no bout adoubt it. What’s the difference?

Drop Vs. Cast

 A cast shadow is anchored at the bottom of the image, and looks more “real” by far. The lack of shadow under the image removes the whole “floating off the background” effect, and it’s a lot closer to what we’re used to seeing in reality.

Great, Mad, where’s the cast shadow button, man? Hook us up!

Well, I regret to inform you that as of this writing Adobe has not provided us with an automated method of achieving this effect. You may go gather your torches & pitchforks now.

Nah, not worth our time. Let’s just learn how to do them ourselves.

Photoshoppers Of The World, UNITE!

Oh, sure, now you tell us!

The first thing we’re going to need is a layer that looks like what we want to shadow, of course. There are a few different ways to accomplish this (which is the part of Photoshop that I personally love, by the way. There’s eighteen ways to do anything).

Pick the layer that you want to cast a shadow. If it’s more than one layer, you have to make a choice: Are all the layers going to be casting one big common shadow, or are shadows from one layer going to logically fall on other layers? Either way, for each shadow you want to cast, we’re going to need a single layer that is filled in black in that shape.

If you have multiple layers, hold down CTRL while you click on each layer that you want to be included in the shadow. When you have them all selected, or if you’re only doing one layer, duplicate them. You can do this by right-clicking and selecting “Duplicate layers”, or just drag them all down to the New Layer icon at the bottom of the layers palette.

New Layer button

This bad boy right here.

If you have multiple layers selected, now’s the time to get it down to one: Merge them (CTRL-E) while they’re all selected (or Layer>Merge Layers, if you prefer the menus, OR right-click in the layers palette and select Merge Layers…. eighteen ways).

When you have the shadow layer now as one layer, we just need to fill that shape with black. The easiest way it to use Color Overlay. It’s on the “fx” menu, where we found the Drop Shadow function. Leave the mode on Normal, 100% Opacity.

Alternatively, you can load a selection based on the pixels used in the layer. This MUST be on a layer with transparency, if you use it on a completely-filled layer, you’re just gong to (SURPRISE!) select the entire canvas, as every pixel was being filled already. The way that works is this: Select the layer you want in the layer palette. Now, holding down your CTRL key, click the layer thumbnail.

Thumbnail Location

This completely different bad boy right here.

If that worked out correctly, you should now see the marching ants doing their little dance around the edge of your layer. You can now fill it with black, by any method you choose (Edit>Fill, CTRL-F5, Right-click in the selection and pick Fill, yada yada yada). Be warned, though… if you have a soft edge on your selection, the edges might only be 50% selected, as they’re only 50% visible. The effect of that is that the very, very edge may not get filled with 100% black. For that reason, I usually use the Color Overlay method.

If you used the color overlay method, you could proceed, but just so we’re all on the same page no matter what methods you’re using, I’d like you to do one more step: The black Color Overlay layer isn’t really black pixels yet. It’s just “coated”, if you will (or even if you won’t. My tutorial). There’s a trick to making the pixels actually turn black, and it will also work for changing anything else you find under the fx menu from an effect to actual pixels. Of course, once you do this you can NEVER remove the fx, so make sure you actually want to do this trick before you use it. No going back.

The trick is, make a new layer. CTRL-SHIFT-N or simply click the new layer button I showed you earlier. Now, select the layer with the shadow fx on it and the new, blank layer. Merge them. Presto, shadow layer with actual black pixels.

Now that you have your shadow, pull the shadow layer below the layer it’s shadowing. Now all we have to do is bend it.

Of all the tools in the box, my favorite by far is Free Transform (CTRL-T). With the shadow layer selected, hit CTRL-T, or if you must, Edit>Free Transform. You should see your layer now has a box with little pull handles around the outside.

What's In The Box?


If you now right-click, you’ll see quite a few options for how you’d like to transform.

Transform Options


The bottom two sections, the rotate and flip options, should be pretty self-explanatory, and we won’t need them for cast shadows. Content-Aware Scale, greyed out in my example, is so far removed from what we’re doing that we’re just going to ignore it for now. Free Transform, at the top….it mystifies me that that’s there. If you click it, it will put you into Free Transform mode… which you were already in. NEXT!

So basically we’re left with Scale, Rotate, Skew, Distort, Perspective, and Warp. Scale locks the handles so that no matter what you pull, all you can affect is the size of the layer. Rotate does much the same thing, only allowing you to rotate the selection. Warp is great for distortions, and will be the subject of a further tutorial, but isn’t really what we want for shadows. That leaves the ones we really need for this project.

Skew allows you to change the rectangle of the box into another quadrilateral (fancy talk for “four-sided figure”).  The way it changes will depend on whether you yank it from the corner or if you use one of the middle handles.


So you can see, the middle handles pretty well keep the length and ratio, just make it more diamond shaped (Trebek says “We would have also accepted parallelogramparallelogram“). Pulling from the corner gives you more of a “vanishing point” view. Which method you will choose depends primarily on the effect you’re going for. In general, middle handles are better for closer shadows like the wall behind someone, and the corner handles are better suited to long oblique shadows like the ones in the referee shop above. The Cast Shadow in the Drop Shadow vs. Cast Shadow above is just a simple middle-handle skew.

Distort works pretty much the same way, except where Skew restricts your movement along one plane, Distort allows you to pull the handles pretty much anywhere you want. The corners still pull independently, and the middle handles move that entire side.

Perspective is a very handy option, and it works in a similar fashion. The difference is that when you pull one of the corner handles, the opposite corner pulls in (or out) to match, giving you a perfect perspective on both sides. This is great for long shadows on the ground (vanishing point shadows)… they get skinnier the farther away from you they get.


Also great if you’re trying to make the monolith from 2001

So now you have the basics for making a shadow fall on a flat floor… what about a wall? Think about how a real shadow looks when it’s falling on the wall behind someone…. the floor part of the shadow still uses the skew method we’ve seen, but when it hits the wall, it behaves much more like a drop shadow. What to do?

Well, we want both a skewed shadow on the floor and a “straight” shadow on the wall. The solution is really simple: Only skew the part that will sit on the floor. Let’s say you start with this:

Begin Shadow Skew

Make a selection of JUST the portion of the shadow that will appear on the floor, like so:

Select Shadow Skew

Now, all you need to do is CTRL-T, Select Skew and pull the bottom middle handle to the right, like so:

Finished Shadow Skew

Keep in mind, and consider before you begin, the surfaces that the shadow would actually hit. If this person were standing in front of a low wall, it might skew again on the top of the wall, and then disappear entirely. DON’T make your shadow just hang there in mid-air. Shadows don’t do that, at least not the ones I’ve met.

Now that you have your shadow shape defined, all that remains is how fuzzy to make it and the opacity. You can make it fuzzier just by adding a little Gaussian blur (Filter>Blur>Gaussian Blur), and you can lower the opacity from the opacity slider on the layers palette.

Depending on the shape of what you’re shadowing, the bottom may not line up quite right. That’s mainly because of the difference in distance from the light source. An easel leg, for example, is almost never going to line up perfectly. But if you use this method, it should be fairly obvious to you where you need to extend or trim a shadow to make the bottom fit. For best results, add or trim the areas that you need to BEFORE you add the Gaussian Blur… it’s pretty hard to match a blur when you’re cloning.

SO….did ya make it all the way through that? I know I barely did. If you’d like to test-drive your new-found shadowing powers, join us in the forums. We’re going to do a showcase and it’s all about the shadows.


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1 Comment

  • #1
    05/01/2012 4:40 am

    Excellent, this is exactly the kind of thing I need. Very informative and highly readable.

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