Curves Are an Abomination

Curves Are an Abomination …and so is the Shadows/Highlights command. Unless, of course, you want to create art that is not photographic; art that specifically is not intended to accurately represent the real world.



Scientists and engineers have spent over a hundred years perfecting all aspects of photographic image capture. Optics for even a cheap point and shoot camera are extraordinarily good; high-end glass is beyond extraordinary. What you get from your camera is as good a record as you can get of the relative values of the light in the scene photographed.
     The reasons why light has fallen on a particular scene in the way that it has are beyond what any person, expert or not, can understand. Every element in that scene (and near, but outside what is included in the photograph) is bouncing, blocking, or absorbing light to a greater or lesser degree—including the sky, and the air. It is not possible for the human mind to comprehend all of the workings of light in a given scene.

Yet, almost every new (and experienced) user of Photoshop will look at a picture for a minute or two, say to himself “That light isn’t right,” jump into the curves dialog, slap a dot (or two…or three, or four…) onto a line in a two inch square proxy, drag it this way and that, eyeball the picture and say, “much better!” As if he or she knows more about light than light itself.
     Curves distort the relative values of light within a picture. There is no justification for such a distortion; the relative values of light are correct as the camera recorded them.
     You may be thinking that Ansel Adams manipulated his pictures in much the same way as curves does. No, he did not. He manipulated all of the tones in a given area (not a given tonal range), by dodging and burning or by manipulating the processing of his negatives or film. He made all of the tones within that area of the picture either brighter or darker, or he made all of the tones more or less compressed (contrast manipulation) but the relative brightness of the tones within that area were always maintained. He never distorted the relative tonal values.
     Levels adjustments also manipulate the tones in an image, but Levels respects the relative tonal values. You can apply a Levels adjustment to a particular part of a picture by using its adjustment layer mask, manipulating local brightness much as Ansel Adams did. The relative values within that area are respected. You can stretch all of the tones or compress all of the tones but you can’t take a limited set of tones and distort them relative to adjacent tones—and throughout the rest of the picture.
     When you apply a curves adjustment, when you drag a point on the tone curve, all tones of that brightness anywhere in the image are distorted. The relative values of those tones are ruined.

Curves are useful for creating hot highlights on fake chrome. They are useful for commercial illustrations where arbitrary color and lighting are what is intended. Otherwise, curves are an abomination.

Layer Masks

Here we are, then. All set with our mask on the layer where we need it. A lot of trouble, but you’ll see, when you work with the mask, that it’s worth it.
     Click on the mask thumbnail (the white square on the masked layer). Any edits made now will be to the mask, and not the image. Confirm that you are in mask edit mode by checking the icon next to the eyeball.

Use the zoom tool to zoom way, way in, and then paint with the paintbrush with a hard edged brush (from the first row in the brushes pop-up palette). Make sure the paintbrush tool’s opacity is set to 100 %.
     Wherever you paint with black, you will see the apple disappear. However, if you paint with white, the apple will reappear. The image, below, shows the round brush cursor stroking the red apple away from where it covers the snake. The apple is not gone; it’s just hidden.
      This is the magic of layer masks. Press the X key on your keyboard to switch back and forth between black and white. (Press D if black and white aren’t the colors showing in your toolbar’s color boxes.)
     Painting a mask with shades of gray will mask the image in proportion to that shade. Painting with the paintbrush tool’s opacity set to 50 % will cause the mask to allow 50 % visibility of the layer’s contents wherever you apply your strokes.
     After adding the mask to the apple, the Layers palette looks like this.

And, the masked part of the image looks like this (the burn tool was used to add shading where the two objects join).

This tutorial is narrowly focused on how to create a layer mask. If you’d like to learn more about the details of combining images, I recommend that you try the two Combining Images tutorials in the Photoshop section.

An Elements user, sent me an excellent technique for simulating layer masks. It works exactly the same as a real layer mask.
It’s faster than making a real layer mask. It looks a little bit confusing in the Layers palette, so you’ll need to make sure and name your layers to remind yourself of what the various layers are doing. Here’s how it goes:

1. In the document to which you want to add a layer mask, add a new adjustment layer (Layer > New Adjustment Layer). Use Brightness/Contrast or Levels. In the dialog box that appears, make no changes—just click OK to add the layer with no alteration. [Do not use one of the Fill layers for this technique. You may think that you can use a fill layer’s mask to avoid the problem described in the Update note below. If you use a Solid Fill layer and have any transparency in the grouped layer above, the fill color will show through. This is not what you want.]
2. Drag the new adjustment layer to be directly under the layer you want to mask. In the case used here, that would be directly below the apple’s layer.
3. Click on the layer that you want to mask (the apple’s layer) and choose Layer > Group with Previous. Or use the shortcut of Alt-clicking on the line between the two layers.
4. Click on the adjustment layer’s mask icon to put the mask into edit mode. Paint on the mask as described in this tutorial. Alt-click on the mask to see it alone, without the image. Alt-Shift click on the mask icon to see the mask as a red rubylith overlay on the image when editing it.

Here is what your Layers palette should look like.
 
This is a beautiful, simple method for getting all the benefits of a true layer mask.

Well, it was too good to be true. There is one flaw with this technique. An Elements user, Don Fukushima, discovered this problem and was kind enough send me an email to let me know about it. If your image has areas that are completely transparent in the (combined) layers below the adjustment layer, you won’t be able to mask the areas on your layer that overlap those transparent areas. If you have a proper background layer (which does not allow transparency) this won’t happen. Real layer masks do not have this problem.]

I hope you are clever enough to notice that adjustment layers and fill layers always have their own layer mask, already in place when you add the layer. All mask editing techniques work on those masks in the same way that they work on a “regular” layer mask. Note that it is usually better to use soft, low opacity brushes to hand-edit adjustment layer masks (and the gradient tool).

Think about that. You therefore have complete control over how much and where that adjustment or fill color is applied. By editing the mask, you can add or remove the adjustment or fill at will. And all without touching the original image below. This is true non-destructive editing.
     
If you want to make use of all of the power that is in Elements, you have to master masks.

Layer Masks

Elements 2 users, you can’t use the shortcut key method that worked in Elements 1, but you can easily add a layer mask by pressing and holding the Alt key as you apply one of the frame effects.
     Go to the Effects Browser, and in the Frames group, choose the Ripple Frame (or the Spatter, or Strokes frame), then press and hold the Alt key as you click the Apply button. Keep pressing the Alt key until the effect has been completed. If you are asked whether you want to Flatten All Layers? or Discard Hidden Layers? click OK to both. Otherwise the effect will not be applied.
     You will now see a layer in the Layers palette with a layer mask. In the illustration below, the cursor is pointing to the mask.

A duplicate of your background layer will have been generated (the middle layer, shown above) and visibility will be turned off for the background layer. Delete the middle duplicate layer, and turn visibility back on for the background layer, if you wish.
     The mask will have black content from the frame effect. Get rid of this by clicking on the mask thumbnail to get into mask edit mode. Confirm that you are in mask edit mode by looking at the icon to the right of the layer’s eyeball icon. When in image edit mode, you will see the paintbrush icon.

When in mask edit mode, you will see the mask icon to the right of they eyeball icon.

Once you have clicked on the mask thumbnail and are sure you are in mask edit mode, press the D key on your keyboard to make sure you have the default mask edit colors (white/fore, black/back—the reverse of the image edit defaults). Then press Alt-backspace to fill the mask with white.
     If you wanted to mask a layer other than your background layer, or if you do not want to flatten your document, there are a number of ways to do it, but the simplest is to duplicate the layer that you wish to mask to a new document, add the mask, and then drag the layer back onto the original file. [Note that you will lose transparency on the masked layer. If that’s a problem, see the techniques in the next part of this tutorial.]
     Do this by right-clicking on the layer, and choosing Duplicate Layer. In the Duplicate Layer dialog, for Destination Document, choose New. Apply the steps described above to the new single-layer document, then drag the masked layer back onto the original file. Be sure to press the Shift key as you drop the dragged layer so it will pin-register onto the original file.

Here it is, about one year since I first posted the original (much longer) layer mask method for Elements 1, and I’ve discovered a way to add a layer mask to any layer in Elements 1 that takes about five seconds. Sigh. Anyway, here is how it’s done:
Press the following keys (in the order given with no other clicking in between!).
Ctrl-A
Ctrl-C
Ctrl-Shift-V
Ctrl-J
For those of you who hate keyboard shortcuts, the menu steps are:
Select > All
Edit > Copy
Edit > Paste Into
Layer > New > Layer via Copy
     After you’ve done those steps, you’ll have your mask, but you need to link the mask to the image. To do this, click between the image thumbnail and the mask thumbnail on the layer.

After you’ve clicked there, you’ll see the little chain icon that tells you the mask is now linked to the image.

And that’s all there is to it. If you already know how masks work and how to edit them, you’re all done. If you don’t know how they work, read through the rest of this tutorial for some tips.

What can you do with a layer mask? Suppose I want to put an apple into an image of a snake, and have it appear that the apple is sitting on the ground behind the snake. Open both files and make the snake picture the active window.
     Since I know that I am going to need to mask the apple, and I also know that I won’t want to flatten the document after I have dragged the apple onto the snake image, I will add my layer mask before I bring the apple onto the snake.
     Do this by opening the base (background) image, in this case the snake picture. Use the steps described above to generate a masked layer. Then delete all image content from that masked layer by clicking on the masked layer in the Layers palette, choosing Select > All and then pressing the Delete key.
     Leave the selection active. Click on the apple’s file to make it the active window. I will have already carefully selected the apple, using the methods described in the Simulating Alpha Channels tutorial. Click on the apple’s layer in the Layers palette. Choose Select > All followed by Edit > Copy.
     Click on the snake document to make it the active window. Click on the (empty) masked layer to select it in the Layers palette, if it is not still selected. Assuming you still have your selection active (if not choose Select > All), choose Edit > Paste Into. Be sure and use the Paste Into command, and not Paste.
     I can now use the layer mask on the apple’s layer to hide those parts of the apple that are supposed to be behind the snake.
     You may be wondering why I didn’t create this mask on the apple image, before moving it onto the snake. Then you wouldn’t even have to bother with extracting it from its original background.
     I prefer to have the edges that will be showing, i.e. the top of the apple, cut rather than masked. I think you can do a much better job of blending the edges if you don’t have to deal with the old background.
     So, why not duplicate the apple layer into a new document (via the Duplicate Layer dialog box) from the image above, and add the layer mask to it there? The first step of the frame effects is to flatten the image. Flattening removes transparency. You then have to again extract the apple from the background. Easy enough with the Magic Wand, right? Maybe, but more likely than not, you’ll have problems with a white halo being left behind as shown below (greatly magnified).
     To find out how to edit your mask, go on to the next page.

Simulated Alpha Channels

Grab the gradient mask layer, and drag it below the original image copy.

For this effect to show properly, we are going to need another layer. Click the New Layer icon at the bottom of the Layers palette. Name the new layer “white layer”. With the new layer selected, press Ctrl-Backspace to fill it with white (assuming you have the default colors showing in the color box; if not, click the default colors icon in the very bottom left corner of your toolbox to make white your background color).
     Drag the white layer to be directly below the original image copy, which will make it the second layer from the top. It will effectively act as a new background.
      Now load the gradient mask layer as a selection. Do this by pressing Ctrl and clicking on the layer’s name. Next, choose Select > Inverse. Then, with the selection active, select the original image copy layer.
     Don’t worry that the selection outline looks wrong; the ‘marching ants’ outline only includes pixels that are more than fifty percent selected. Since the gradient fades to full transparency, its transparent edge will fall below this threshold, but those pixels are selected to the degree that they are opaque. This is what makes masks so useful.
     Press the Delete key. Your image should appear as shown below. The white you see is the new white background layer showing through. Pixels have been deleted from the image to the degree that they were selected.

Gradient masks are very useful for blending one image into another, or for any kind of transition. At the bottom of the page you can see where I’ve added some text to the new white area.

You can create any kind of mask you like using any of the editing tools. Opacity is the only factor that determines the degree of selection that will result from your mask. You can use any color you like, and paint any outline or shape that you like. You might try experimenting with the paintbrush on an empty layer. Try different brushes with an opacity of 30 %.
     You do have to be sure and remember the steps necessary to load your selection.

1. Select your mask layer. It should be stored below the visible layers at the bottom of the image.
2. Press the Ctrl key, and click on the mask layer’s name.
3. If necessary, choose Select > Inverse. Remember, the selection is for the areas that are painted black. In the example I used, the flower was not black, so it was necessary to invert the selection in order to select the flower.
4. Click on the image’s layer (“original image copy”). This is important! I forgot to do this just about every time I went to use my selection. Make sure you choose your image layer after activating the selection outline from the mask layer.
5. And, that’s it. You can apply filters, cut, copy, move, and color selections. You should be able to take advantage of many of the lessons in Photoshop books, as well as online tutorials that require alpha channels or any kind of complicated selections.
6. When you are ready to output your image, save a copy with the mask layers, and then delete them from the copy your are outputting.

An alternate, and possibly better method for simulating an alpha channel was suggested by Richard Coencas in the Elements User to User forum at Adobe.com. It goes as follows:

1. Select the layer which contains the object you want to select and mask.
2. Click the little black and white circle at the bottom of the Layers palette, and choose Brightness/Contrast, or Levels from the menu (it doesn’t matter which).
3. When the adjustment dialog box appears, do not make any changes—simply click OK. This adds an adjustment layer without changing your image in any way.
4. Select the adjustment layer you just added, and, while pressing the Shift and Alt keys, click on the white square.
   
5. Choose a hard edged brush, and paint with black on the image, around the outside of the object you want to select. Wherever you paint, you will see a partially transparent red color. This is the rubylith mask. Use black to add to the mask, and switch to white to remove any mistakes.
   
6. When you’re satisfied with your outline, press the Alt and Shift keys and click the mask again, then press Alt alone and click the mask. You will then see the mask, alone (without the underlying image) in black and white. Check to see that you’ve made the black parts of your mask fully opaque.
   
7. To load your adjustment layer mask as a selection, press Ctrl and click on the mask. Then switch to the image layer. Don’t forget to do this! You don’t want to select the adjustment, you want to select the image object.
8. The advantage of this method is that you don’t need to drag the layer below the background. This is a layer mask and it only affects the layer it is attached to, which in this case, is an adjustment with zero change. “Real” layer masks, which this is, are not visible in the image. But, no, this layer mask can’t be applied directly to an image layer like you can in Photoshop—you still have to load the selection and then switch to your image layer.
9. The disadvantage is that you may or may not like working with the red, rubylith color.

[This is only for Elements 1 users. In Elements 2, you have the ability to save and load alpha channels via Select > Save Selection. However, you can't see or edit your alphas.]
If you have a document which you know contains an alpha channel, there is a way to make the alpha channel visible, and therefore useable in Elements.
     You may have received files created in Photoshop which you contain alpha channels. Also, most 3D programs will allow you to create an alpha channel matte of objects in your scene during an image render.
    This technique just occurred to me and I’m posting it in text only, for you to play with. I’m in the middle of another project right now, and don’t have time to add illustrations or perfect the method. (This is not included on the .pdf for this tutorial). Please let me know if you find a way to refine the edges of the revealed alpha. Here is a zipped .psd file (7 KB) which includes an alpha channel. I’ve copied the contents of the alpha to a layer, so you can see if you’re matching the alpha when using this method. Okay, here are the steps:

1. With your .psd file open in Elements, create a new layer at the top of the stack and fill it with white.
2. Choose Filter > Render > Lighting Effects.
3. In the Lighting Effects dialog box, choose Omni from the Light Type menu at the top.
4. At the bottom of the dialog box, choose Alpha 1 (or whatever your alpha is called) from the Texture Channel menu. You’ll have to scroll to see it.
5. Make sure White is High is checked, and move the Height slider towards Mountainous just enough to make the alpha outline clear in the preview window.
6. In the preview window, if necessary, drag and manipulate the Omni thingy to center it over the alpha shape. Then click OK to exit the dialog.
7. You should see a black outline of your alpha on your new white layer. With that layer selected in the Layers palette, choose Filter > Other > Maximum. Set Radius to 1 pixel and click OK.
8. This is as far as I can take you. You should be within one pixel of recreating the alpha channel. However, that one pixel fringe is a problem. There is probably a way to get rid of it, but I haven’t the time to spend diddling with it. Help!
9. You can play with Enhance > Brightness/Contrast > Levels. However, while this sharpens and intensifies the black outline, it shrinks it. You can try using Select > Modify > Contract (or Expand).
10. To see how closely you’re matching the reference layer I created for you (by copying the alpha to a layer), create a new layer at the to of the stack. Use the magic wand with Tolerance set to zero, and Contiguous checked to select the white area outside your outline and fill it with black (on the new layer). Change that layer’s blend mode to Difference. Turn off the outline layer’s visibility. If the image is totally black, you have a perfect match. If you see a fringe outline, it’s not.

Simulated Alpha Channels

With the mask corrected, and the flower layer’s visibility turned back on, the image looked as shown below. The last step is to grab the completed alpha channel layer (click on the layer name and drag) and move it below the original image copy.

Then turn off visibility of the alpha channel layer by clicking on the eyeball icon.
     Any time you want to select the flower, go to the alpha channel layer. Press the Ctrl key, and click on the alpha channel layer name. This loads the layer’s transparency mask. What that means is it selects all pixels according to their opacity.
     Since the black area is where the flower is not, we need to invert the selection. In the menu bar at the top of your window, choose Select > Inverse. With the selection active, select the flower’s layer (“original image copy”).
      The flower is now selected, and ready to do with as you will. In my Photoshop Combining Images tutorial in the Photoshop section, I dragged this same flower onto another image using a quick mask selection which is the equivalent of what we have just done.

What else can you do with simulated alpha channels? Regular Photoshop users can probably figure this out for themselves, but I believe you can do many things that you can do with a true alpha channel.
     Lets try adding a gradient mask to the flower image. If your flower is selected, deselect it by choosing Select > Deselect, or pressing Ctrl-D. Then click on the New Layer button at the bottom of the layers palette. Drag the new layer to be at the top of the stack, if it is not there already, and then rename it, “gradient mask”.
     Choose the gradient tool in the toolbox.

In the gradient tool’s options bar click the little down arrow next to the gradient thumbnail (not the thumbnail itself) to access the pop-up palette. Choose the Foreground to Transparent gradient, as shown. It’s second from the left in the top row.

Choose the linear gradient. It’s the left most one on the options bar just to the right of the Edit button.

The rest of your gradient tool’s options bar should appear as shown below.
     Make sure the new gradient mask layer is selected in the layers palette. Then click on the flower image just to the right of the flower’s yellow center, and drag straight across to the image’s right edge. The result, as shown below looks, well, very black. Don’t worry. I know what I’m doing … I think.