Black should be only 100%K, not composite from all colors
You have to keep in mind that printing process has minimum 4 passes (to print full color – in Offset technology), and that alignment of these four passes may not be 100% same. Every pass is one color. So if you make text from 100C 100M 100Y 100K composite, you will have noise at letter’s edges. Photoshop has habit to form black from all composites so pay attention to select only pure black (0C 0M 0Y 100K) when you write text.

Use minimum 300DPI for Offset and 600DPI for Digital printings
Human eye can easily notice granulation of image raster if its resolution is lower than 96 DPI. Common Offset printing plates (machines) support 300DPI, so use this quality and make design in that resolution. Also, some digital printers support more dots per inch so you can make design from 600 to 1200 DPI’s, but it is very hard to notice difference between 600 DPI and higher. In special cases if you make design for buildboard, you can use 30 DPI, because of view distance.   

Clean up small composite values
Keep in mind that every colored surface is made from these 4 components mentioned before. If you have on some surface less then 10% of some color, it is better to modify that color component to 0% in order to avoid edge noise. You will make small change on color. Also if you try to print 5% of some composite it is very small chance that something will be printed at all on Offset printing.  
Example: if you fill background with gray color: 5C 5M 5Y 5K you will probably bet totally white surface, but, if you use 0C 0M 0Y 11K, which gives very similar color on screen, you will have some gray color on background.
Simply, printing and screening technologies are different.

Make from 3 to 5 mm bleed on every edge that should be trimmed
Printing surface is always bigger than required dimensions. When you do screen design you don’t think about cutting, because it doesn’t exist on screen, but, when you do design for paper you have to keep in mind that someone will have to cut edges of your design. So there is Trimmed dimensions and Not-Trimmed. As designer you are thinking in trimmed dimensions, but when you send file on printing you have to make tolerance in case that swings that cuts paper to fit required dimensions make mistake, and, it always make some mistake. If you don’t make your design bigger you will have white stripes at edges of your catalogue or flyer.   

Keep in mind that US print shops use the English system religiously. In case you didn’t know, points and picas come from the English system, and its much easier for us to use all of our technology with those measurements. The bleed (that’s the area of excess design to allow for cutting) is always 1/8″ or less depending on the room on the plates.   

In case of flyer, you have to make this bleed for all edges, in case of catalogue, only outer edges should have this because, edge that comes to bending line doesn’t have cutting.

Make margins at least 5mm
All elements of design and all texts should be at least 5mm from edge of cut. I tried with 3mm, it was bad looking because on some places distance was smaller because problem of swings. In some cases you can go up to 10mm of margin.   

That is something that I noticed that beginners in graphic design should know. There is also some pure design tips about contrasts and colors, but I’ll leave it for some other tutorial.   

Use TIFF as final file format
I advise you to use TIFF format when you send design to printer company. I had cooperation with many printing companies and printing professionals and everybody agree that TIFF / CMYK is most trusted image format for color-safe exporting and transporting from design workstation to film exposition company.   

It is safe to use: LZW compression (more compatible) or ZIP compression (less compatible). For final file you can discard layers to reduce file size. Skilled print workers reported that ZIP compression may lead to corruption later on in the process of printing, also that LZW compression is not allowed by some applications (Heidelburg).   

Check http://www.omnetwork.net for more tutorials covering this and other design topics.

About author: Goran Grubic is skilled print and web designer from Serbia running design portal omnetwork.net (http://www.omnetwork.net/) which offers for free large unique tutorial library (covering Photoshop, Flash, 3D Studio, Dreamweaver and similar topics), free graphic resources (templates, elements, 3D models etc.), photography (free&royalty free, just use it!) and sounds&music loops for multimedia web development.

This example shows how to Load, Add, Subtract, and Intersect selections between overlapping layers just with quick thumbnail clicks.

Load Pixels to Selections

In “Layer 2″ Command-click to load a fill as a selection. Any pixel which is not transparent in “Layer 2″ will be loaded as a selection. This is not the same as copying the layer, only its outline. The green fill shows the selected region although you will get only the surrounding Marquee. Let’s call this state (with “Layer 2″ selected) the initial state.

Addition

With the “Layer 2″ loaded as a selection, Command + Shift-click on “Layer 1″ to add it to the selection. Now non-transparent pixels of both “Layer 1″ and “Layer 2″ are combined as the new selection. Notice the small plus sign in the Command-Click box.

Subtraction

Revert to the initial state and Command + Alt-click on “Layer 1.” This will subtract any overlapping pixel of “Layer 1″ from the current selection of “Layer 2.” Notice the minus sign.

Intersection

Revert to initial state and Command + Alt + Shift-click on “Layer 1″ to keep only the overlapping pixels as a selection. Notice the X sign. If the layers are not overlapping this action will deselect all.

Garbage Masks

Garbage Masks are created to roughly isolate the ‘region of interest’ from rest of the image. Further trimming is carried out inside the Garbage Mask with precision.

Vector and Raster Selections

Draw an outline around the region of interest in the image with any of the Lasso Tools and double-click to complete the selection. A Garbage Mask needs to be saved for further refining, which can be done both as a Layer or Vector Mask. We must choose it depending on complexity of the outline and how we are planning to trim it later on. With the Lasso selection click Add Layer Mask to save it as a Layer Mask.

Alternatively, we can also save the selection as a Vector Mask which can be later refined by working on the shape spline that defines its outline. With the Lasso selection still intact (2), go to the Paths tab (3b) and click Make Working Path from the Selection button at the bottom. This will save the selection outline as a Shape Working Path.

Now load the selection again, and return to Layers tab. Click Add Layer Mask once to create a Layer Mask (Command-click to load again) then click the same button( 6b) once more to Add Vector Mask. Saving selections as Vector Masks or Shapes saves memory.

Selecting with Vector Mask

Click on the Vector Mask to activate it. Or selecting any of the Shape tools will make it active. Vector Masks are modified by adjusting the spline positions (Control Points) and curvature (Tangents). You can disable, delete, or save the Layer Mask with another Layer. The Convert Point tool is most suitable for altering Vector shapes and Paths. Click and drag on the handles, then Command-click on control points to move them.

Once a acceptable outline has been achieved use the Add Points tool to refine and further match the outlines. Delete points when necessary. Dragging handles with Command + Shift will lock their relative slopes. Drag directly on the Control Point to reset handles. Regular curvy shapes are best to be extracted with this process.

This method is also best in situations where boundaries are not clearly visible.

Select by Color Range

Selecting by color is the fastest way to Chroma select. Click Select > Color Range and select a color with the Eyedropper Tool available. Once selected certain shades can be removed selectively with the Minus (-) Eyedropper or again added with the Plus (+) Eyedropper. There is also a preview window that displays the selected region or the original image.

This tool can be used to setup Garbage Masks around the subject and later refine it with editing the Mask. Select by color is not a one-click solution, but does a great job in minimizing manual work.

Chroma from Channels

Color information of each type are stored in as separate channels, which can be viewed in the Channels Tab. We can use the channel wise variations in color intensities for selecting objects in the image. This process is helpful only when background and foreground have separate color distribution in at least one channel.

Advanced Chroma

In the Histogram we can see that the blue channel is predominant in the image and it extends up to the highlights where other channels are very weak. Our subject here is the patch of vegetation in foreground.

Picking the Best Channel

A simple observation of the three channels tell us that the blue channel has the highest contrast between the Sky and Grass. We are going to exploit this property to separate the two. Duplicate (Command + J) the Layer and go to the Blue channel of the Copied layer. Click Image > Adjustments > Curves or Press Command + M to apply curves modification on the current channel.

Applying Curves

Select the point closer to the dark grays of the channel and drag it (2) forward in the x-axis (horizontally) keeping y-axis at 0 (shown by the small circle). This will make the darker pixels uniformly more darker. It shouldn’t affect the background, drag it a little back to left if it does.

Next, select another point closer to the White Point, drag it (3) back towards the midtones keeping the y-axis(vertical) at maximum (shown by the small circle). What we are doing is saturating the dragged range of blue up to 100%. Make sure the whole background turns white or almost so, and there is a very high contrast between the Grass and Sky.

Channel as Mask

Command-click on the channel thumbnail to load the channel into the selection. Areas which are predominantly blue will be selected totally and the rest according to respective degrees. Areas which have no blue (the black parts) will be left from the selection. With the selection in place go to the Layers tab and click Add Layer Mask to save the selection as a Mask.

Inverting the Mask

Press Command + I to invert the Layer Mask.

Selecting by Brushing on Masks

Brush based selection is used to extract foregrounds with complex outlines with accuracy. It is also used to refine selections made with other techniques. And it also support transparency (softness).

Erasing is probably the first thing that comes to mind when we talk about brush based selection. But it is not a recommended process at all. Erasing is a destructive process and can permanently damage the original image as recovery is limited only to a number of undo levels we have set.

Brushing with Layer Masks

Here too Layer Masks can be used, to preserve the workflow of Eraser and additional possibility of recoveringremoved portions if they are needed. Painting on the Layer Mask with a White or Black will reveal or hide the contents respectively. We can brush out backgrounds in the same way as in using the Eraser tool and get it back by painting with White.

No Feedback

When brushing the mask we may sometimes trim off relevant parts accidently and keep focusing on the wrong silhouette only to be discovered later. This is highly probable when foreground background have similar hues and there is no immediate visual feedback.

Immediate Feedback

This problem can be averted by following a simple rule of keeping a multiplied duplicate of the current layer in the background as a guide layer. Multiplied gradient maps will show-up as high contrast versions of the subject outlines if violated.

Luma Select

As already mentioned Luma is the illumination levels of an image. Luma can be used to extract components from the image which have a considerable brightness difference than others.

Simplest Luma Hack

Unlock the background and make a duplicate of it, then hide the original Layer.

Apply Threshold

Apply a Threshold Adjustment Layer on top. You will notice that some parts of the image have been turned instantly black and rest are pure white, and there are no intermediate grayscale levels.

Adjust Threshold

Adjust the Threshold Slider and try to enclose the subject or background (whichever is darker) in black. Hide the Threshold layer and look at the original image for guidance when required.

Merge Layers

Command-click to select the top two layers and Merge them into one. Select the bottom layer, make it visible and create a blank Layer Mask.

Add Layer Mask

Copy the merged image and paste to the Layer Mask, following the process discussed above. We have our Layer Mask ready, but in most cases there will be holes and parts of our background visible. Use the Mask Painting technique discussed above to make it tidy. Invert if necessary.

Luma Select with Transparency

The Threshold technique discussed above is very fast to implement, but is only useful for extracting solid objects as it lacks transparency. The following method can be useful in situations where we need Luma extraction with transparency. Here we are going to remove the ice-water from the rest of the rocks.

Using Luma to Mask with Transparency

Unlock and Create a layer from the background (1). Apply an Adjustment Layer Black and White on top and then a Brightness-Contrast Adjustment Layer above it.

Reduce Brightness

Select Use Legacy mode and slowly move the Brightness slider to left, try to get as many black areas from the rocks as possible. This process will reduce the brightness of the Water too so don’t overdo it.

Increase Contrast

Now slowly increase the Contrast slider to the right. With each increase dark-grays will turn to black and lighter grays will glow more brightly. We are going to get the whites as opaque and grays as semi-transparent. Try to get both Whites and Grays where necessary. Over increasing the contrast will make it look like a Threshold Layer, if so there will be no translucency left.

Merge the Layers

When satisfied with the results Merge the top three Layers. Go to the background layer and Add a Layer Mask and copy the merged Layer into the Layer Mask.

Yet Another Possibility

Other than the above two procedures there is also another way of Luma based extraction using the Lab color method.

Lab Color Technique

Open an image and turn it to Lab Color mode by clicking Image> Mode> Lab Color. Goto Channels Tab and find the lightness channel or press Ctrl+1 to directly select it. This is where the illumination levels of all pixels are indexed in the Lab Color mode. You can play with that channel and try to isolate some element from the background. Don’t forget to duplicate the Layer or the Channel before you alter any channel.

And filters that doesn’t work on the image in Lab Color mode works on the Lightness channel, and yield almost similar results.

Conclusion

Photoshop has quite a few options when it comes to selection techniques. Try applying some of these solutions in your workflow to increase your productivity and effectiveness.

]]> http://bhuwant.com.np/blog/2009/07/a-comprehensive-introduction-to-photoshop-selection-techniques/feed/ 0 http://bhuwant.com.np/blog/2009/07/photoshop-selection-techniques/ http://bhuwant.com.np/blog/2009/07/photoshop-selection-techniques/#comments Wed, 15 Jul 2009 12:26:50 +0000 admin http://bhuwant.com.np/?p=317 0px; padding-right: 0px; padding-left: 0px; outline-width: 0px; outline-style: initial; outline-color: initial; font-style: inherit; vertical-align: baseline; font-family: Helvetica, Arial, sans-serif; font-weight: bold; color: #27221f; font-size: 2.7em; letter-spacing: -0.04em; line-height: 1.05em; padding-bottom: 10px; margin-top: 30px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px; border: 0px initial initial;”>Selection in Photoshop

Photoshop selects pixels based one of the three properties, as shown in the image below:

1. Chroma: is the color of the pixel. Color of a pixel is the level of RGB values and color based select tools like the Magic Wand. Select by color uses the RGB% as a criteria to group pixels based on the set tolerance values.
2. Luma: is a selection based on Illumination levels. Illumination levels are whiteness of the image, which is nothing but higher values for all the three R, G and B channels. Photoshop doesn’t have a native interface for a Luma based selection, but many existing tools can be hacked to get a similar result.
3. Masks: are based on spatial position. Pixels are selected and discarded or masked by a parallel layer bound to corresponding image layer. Masks are grayscale and brightness of the mask is called an Alpha level, which is the degree of opaqueness of the corresponding layer pixel. It’s also called the Transparency/Opacity channel as in RGBA etc.

A Note on Masks

In this article, words like Masks and Alpha will be used interchangeably. The process of transferring images to layer masks will be shown once and then used repeatedly without explicitly mentioning thereafter.

Step 1

Open a new image that you want to use as a mask. Double-click the background layer and create a new layer, which is “Layer 0.” Make a new layer, which is “Layer 1,” on top of it and fill with a uniform color, then hide “Layer 1.”

Step 2

Go to “Layer 0″ and click Select > Select All (Command + A) to select all pixels. Next, click Edit > Copy (Command + C) to copy all pixels to the clipboard.

Step 3

Go to “Layer 1″ and create an empty Layer Mask. Initially an all transparent Layer Mask will be created. Alt-click the layer mask to see it in the canvas.

Step 4

With the Layer Mask visible, paste onto the canvas by clicking Edit > Paste (Command + V). A grayscale version of the copied image will be pasted in as the layer mask.

Step 5

Click on the fill layer thumbnail (not mask) to see the result. Any image can be applied as a Layer Mask to another layer. The opacity of the layer will be controlled by grayscale level of the mask.

More on Masks

The easiest way of creating a Layer Mask is to click the Add Layer Mask button with something selected on the canvas. The selection will be saved as a layer mask attached to the current layer and everything outside the selection marquee will be masked and hidden.

Activate Layer Masks

Alt-clicking on the Layer Mask makes it active for editing. Only activated layer masks can be edited which are represented by a thin white outline around them.

Add Shapes to Layer Masks

Dragging any shape onto the canvas while a layer mask has been activated will draw it on the Mask instead of the layer itself. To draw it again on the layer we need to deactivate the Mask by clicking on the layer thumbnail.

Add Brush Strokes to Layer Masks

The same is true for brush strokes. Anything painted on the canvas with a Layer Mask selected will draw it on the Mask instead of the Layer. We can use this property to select objects with irregular boundaries from backgrounds, by painting everything else black on the Layer Mask. White brush strokes will reveal and blacks will conceal.

Copying a Layer Mask to Another Layer

Finally, we can transfer the Layer Mask to another layers by simply loading it as a selection (Command-click) and unloading as we did in the first step by clicking the Add Layer Mask button. Or by Alt-dragging the mask to another Layer (Not Shown).

Technique One: Images with Plain Backgrounds

The best photos are those professional studio type shots that are taken against a plain white background. These shots make it much easier to find the edges of the subject, but trimming out fine hairs can still be a little tricky. In this example we’ll be using the common Channel technique to trim out this lovely lady.

Open up your image in Photoshop. This particular image doesn’t have a pure white background, but it is a plain colour and has good contrast between the subject and grey backdrop.

Head over to the Channels palette and review each of the Red, Green and Blue channels. Each one will be made up of slightly different tones, pick the one with the most contrast between foreground and background. Drag this channel onto the new channel icon to duplicate it.

With only the new channel selected, adjust the Levels (CMD+L) to dramatically increase the contrast between light and dark areas. However, don’t go too far, as you’ll notice some horrendous pixilation appearing in the fine areas.

Due to the slight variation in tone of the background, it appears grey in the darker areas. Use the Dodge tool set to a low Opacity to target the highlights and brush over this background area to really brighten it up.

Switch over to the Burn tool and target the shadows to dramatically darken down the inner areas of the image to pure black.

Use the brush tool to finish off the blacks by painting over the remaining areas of the inner section of the image.

Inverse the image to switch over the black and white areas (CMD+I), and give a quick check for any stray areas that may have been missed by the brush.

CMD+Click the Channel thumbnail to load the selection, then turn back on the visibility of the original channels. Head back over to the Layers palette and copy the selection. Paste it on a new layer and hide the original to see the cut out image against transparency.

The selection has managed to trim out even the finest of hairs to give a realistic cut. Paste the photo against an alternate background. Zoom in and check for any light coloured fringes around the edges, especially if placed against a darker background. These can be reduced using the Burn tool set to Highlights and gently brushed over the outline of the image.

Technique Two: Images with Detailed Backgrounds

The Channels technique is all well and good for studio photography with plain backgrounds, but it gets a little more difficult on standard shots with detailed backgrounds getting in the way.

Open up your image in Photoshop. This image has a decent contrast between foreground and background, but certain areas of the hair do blend in with the darker tones of the backdrop.

Start by trimming out the clear edges with the Pen Tool, but when you reach the hair simply create a rough tracing.

Around the hair portion, aim to include only solid areas of hair that aren’t merging with the background, otherwise the lighter tones will mess things up later.

Make a selection with a feathering of 0.2 pixels to remove any harsh edges then paste onto a new layer. Reduce the transparency of the image so that the original hair line can just be seen.

Here’s where the fun begins! Use the Smudge Tool to draw in areas of new hair, using the original outline as a template. Begin with a 4px brush to flesh out the thick base hair and disguise the jaggy lines from the path. A Wacom Graphics Tablet really comes in handy here to speed up the process and help add varied line thicknesses.

The new hair will soon flesh out the image back to its original appearance. It doesn’t look too bad at this stage, but repeating the process with a thinner brush will draw in those individual hairs.

Use a 2px brush with the Smudge Tool to draw thin stray hairs in varied directions to add realism to the image.

The photo can then be placed on any background with ease, and displays a crisp cut-out with no fringing or loss of fine detail.