by Terry Hemphill

Created

July 29, 2013

Image Trace in Illustrator — a Tutorial and Guide

Image Trace in Adobe Illustrator lets you convert raster images to editable vectors using a new tracing engine introduced in Illustrator CS6. With this fresh approach to tracing, you can quickly get premium results with image sensing that automatically applies the most appropriate tracing preset. And you still have full control to finesse your tracing with an Image Trace panel that presents all options in one place.

If you’re familiar with the old Live Trace feature, you’ll find the new interface more intuitive and interactive. You also get cleaner lines, more accurate fitting, better color recognition, and more reliable results thanks to the refined technology.

Image Trace panel

Introduction

Image Trace replaces the Live Trace feature in previous versions of Illustrator. Both Image Trace and Live Trace convert images to vectors (editable line art) and feature presets for easily creating various effects. Beyond the presets in the new Image Trace, you will find that the sliders and check boxes are different from those in Live Trace, both in quantity and often in purpose. And Image Trace produces far better results, more quickly, using intuitive, easy controls. No more struggling with complex options.

This tutorial and guide covers how to use most of the new sliders and checkboxes, and includes a brief overview of the presets. Discover the ease of use of Image Trace by exploring these sections:

Part 1: Orientation: Anatomy of the Image Trace panel

    1. Presets
    2. View
    3. Mode
    4. Palette
    5. Colors

    Part 2: Overview: Quick start-to-finish trace using presets

      1. Place an image
      2. Choose among presets
      3. Expand the tracing

      Part 3: In Depth: Colors with palette selection

        1. Limited palette
        2. Full Tone palette
        3. Automatic palette
        4. Document Library palette
        5. Mode menu

        Part 4: In Depth: Assigning pixels to shapes

          1. Pixel assignment
          2. Noise slider
          3. Strokes and Fills

          Part 5: In Depth: Precise paths with curve fitting

            1. The Paths slider
            2. The Corners slider
            3. The Snap to Lines checkbox
            4. Abutting versus Overlapping paths

            Part 6: Wrapping up

             

            Part 1: Orientation: Anatomy of the Image Trace panel

            Here is a brief tour of the Image Trace panel. Begin by creating a new document in Illustrator. Switch to the Tracing workspace so that you can see the Image Trace and other relevant panels.

            Tracing workspace

            Place an image for tracing into your Illustrator artboard. When the image is selected, you can see that the options in the Image Trace panel become available. At the top of the panel are the basic options; you can expose additional options by turning the triangle next to the Advanced label.
            The Tracing workspace opens the Image Trace panel and others particularly useful for tracing.

            1. Presets
              The icons located across the top of the panel are shortcuts named according to popular workflows. Choosing one of these will set all the variables needed to produce that related tracing result. Additional presets are accessible in the top drop-down menu.
            2. View
              Beneath the Presets menu is the View drop-down menu. This controls what you see after tracing.
            3. Mode
              The Mode drop-down menu provides choices that define basic color versus grayscale modes for your traced artwork.
            4. Palette
              The Palette menu determines how colors will be chosen for the output artwork. These important options will be discussed in detail later in this document, but for now here are brief descriptions:
              Automatic—automatically switches between limited palette and full tone for the tracing, depending on the input image
              Limited—uses a small set of colors for the tracing palette
              Full Tone—best for photos, creates photorealistic artwork
              Document Library—uses an existing color group for the tracing palette
            5. Colors
              The Colors slider generates slightly different results depending on the value selected for Mode, but in all cases the traced artwork gets more complicated as the slider is moved from left to right.

            Image Trace panel

             

             

            Part 2: Overview: Quick start-to-finish trace using presets

            Here is a quick way to achieve a great tracing by taking advantage of the presets in Image Trace.

            Preset advanced tip

            1. Place an image
              In the previous section of this tutorial you may have already completed this step, but to get started, create a new document in Illustrator and place the image that you wish to trace in the document. Select the image and check that the Image Trace panel is showing.
            2. Choose among presets
              The row of icons across the top of the Image Trace panel are shortcuts that set the values of all the other sliders to achieve conversion for pre-determined workflow. Here are descriptions of the icons and their effects from left to right:
              Auto Color—creates a posterized image from photo or artwork.
              High Color—creates photorealistic artwork of high fidelity.
              Low Color—creates simplified photorealistic artwork.
              Grayscale—traces the artwork to shades of gray.
              Black and White—simplifies the image to black-and-white artwork.

            Results of Image Trace Presets

            1. Expand the tracing
              To finish your quick trace, choose the Expand button in the Control panel at the top of your workspace. Note that when you do so, your placed image is replaced by your new vector objects.
            Expand the tracing

             

            Part 3: In Depth: Colors with palette selection
            Now that you’ve seen the basics, here are details that you can use to refine your tracing and get exactly the effect you want. There are three fundamental behind-the-scenes steps to convert an image into vector artwork. The first is choosing a palette of colors for the traced artwork.

            Image_012a

            Under the hood, Image Trace can choose among four different ways to select colors for the tracing palette. They correspond to the four options you see in the Palette pull down menu. These options determine the number of colors allowed in your traced artwork and how they are chosen from the source image.

            1. Automatic palette selection
              Automatic does the choosing for you. It analyzes your image, and in the case of a photo, generally using a palette that is full tone to create a high-fidelity rendering. If Image Trace detects a fewer colors in the image, it will do a limited palette tracing.

              When you select Automatic for your palette, you can adjust the color accuracy setting. The Colors slider shows a number that indicates your trade-off between vector simplicity and accuracy in the tracing. The value 0 means simplified at the expense of accuracy and 100 means accurate, or photorealistic, at the expense of simplicity.

              Summary: Automatic is a good starting setting as it will generally get the number of colors right off the bat. Automatic can be a better choice than Limited if you want to reduce the number of colors in a photo.

              Limited palette selectoin

            2. Limited palette selection
              Limited allows fewer colors in the palette. In cases where there are fewer colors in the image than the maximum, then the number of distinct colors in the image are used. Where there are more colors in the image than the maximum, Image Trace uses two strategies to select colors for the palette:

              1. Chooses colors that have many similar colors, close together.
              2. Chooses colors that take up the most area, leaving out less-represented colors.

              You can use the Color slider to further reduce the colors selected. However, in cases where the number of colors selected by the slider is less that the number of colors in the image or the image is a photo with a lot of gradually changing colors, the result may seem drab. Brighter colors that occur in small areas may be omitted.

              Summary: Limited is a good choice for tracing artwork with fewer colors, but sometimes not a good choice for photos.
               

            3. Full Tone palette selection
              Full Tone determines the color palette by grouping adjacent pixels of similar color together in your image to create each filled region in the result.

              The Color slider determines the variability of the pixels that make up each of those fill regions. When the slider is to the right, that variability is smaller, resulting in more paths defined by smaller areas of color. When the slider is to the left, the fill areas are fewer and larger. The color chosen for each fill is simply the color most similar to all the pixels within the fill area.

              Summary: Full tone works great for photos and results in the best color fidelity. If you try to use Full Tone with an image that has few colors, forcing the slider to the right can cause artifacts to be picked up as colors — you may get many tiny fills that look like noise.

            4. Document Library palette selection

              White is a color in Image Trace

              Document Library allows you to define the exact colors you want in your traced artwork. You can load any library of colors into your document via your Swatches panel and it will appear here as a choice for your tracing palette.

              Each color in your input image will be mapped to the closest match in the color group you have selected. This sometimes produces unexpected results, especially where colors bleed into each other. By adjusting the noise slider you can sometimes control these artifacts.

              Summary: Document Library is useful if you wish to precisely define the colors used in your tracing.

            5. Mode menu
              The palette choices are available when you are in the Color Mode. If you choose Grayscale or Black and White, your choice of palette menu is removed, but also reveals sliders that allow you to control the way the tones are determined. When you choose Grayscale, the Full, Limited, and Automatic parameters apply as you use the Grays slider. When you choose Black and White, the Threshold slider allows you to adjust the black-to-white transition.

            6. Try it
              In your Illustrator document, select the image you have placed for tracing and in the Image Trace panel, ensure that Preview is checked. Set the Mode to Color, and choose the each of the Palette options in turn. Note that the resolution of your placed image determines the speed of the tracing.

            Image Trace settings and results.

            Part 4: In Depth: Assigning pixels to shapes
            Image Trace must somehow decide which pixels in the image will correspond to which fills or strokes in the output artwork. It sets a group of pixels in a particular region to correspond to a fill or stroke in the tracing.

            There are two ways to approach this grouping, or pixel assignment, determined by the color palette parameters you choose in the Image Trace panel.

            1. Pixel assignment
              If you’ve chosen the color palette Full Tone, pixels are grouped with adjacent pixels of similar color. Such groups grow as long as there are adjacent pixels with a similar color. This is Full Tone Pixel Assignment.

              If any other palette is selected, then pixels are assigned to groups mostly by which palette color they are closest to. This is Assignment by Color.

              Full Tone Pixel Assignment has some advantages over Assignment by Color. First, it often detects when the colors bleed from one region to another, which you can choose to eliminate by moving the color slider to the left. Second, Full Tone Pixel Assignment is designed to remove small groups of pixels of colors unrelated to surrounding colors (noise).

              Assignment by Color, on the other hand, does not go to any special lengths to remove noise or bleed areas. This behind-the-scenes information is helpful you if you need extra control over how colors are mapped from your image to your vector art.

            2. Noise Slider
              For direct control over noise and some control over bleeds, see the Noise slider in the advanced section of the Image Trace panel. The values on the Noise slider indicate the smallest number of pixels per region allowed. Regions with fewer pixels than set with the slider will be considered noise and removed from the final traced output.

              Noise Slider Tip #1: If you have a high resolution image you will usually need to move the Noise slider to a higher value (for example in the 20–50 range) to have some effect. For a low resolution image, set it lower (1–10).

              Noise Slider Tip #2: If your image is low resolution or has detail you wish to maintain down to the pixel level, be sure to adjust the Noise slider all or nearly all the way to the left. Otherwise important details in the image may be omitted when you trace.

              Noise Slider controls in Image Trace

              In your Illustrator artwork, select your image to be traced, choose the palette Automatic and preview the results. Set the Noise slider to a value of 9, then set it to 85 and see the difference.

            3. Strokes and Fills
              In the Advanced panel see two checkboxes next to the label Create, called Fills and Strokes. Most of the time you’ll be in Color Mode and you’ll see that these boxes are grayed out. With color tracings, you always get fills so these parameters don’t apply.

              What makes a line

              The additional ability to create strokes happens with black and white tracings. Presets that are outlines, drawings, or any that operate in black and white mode allow results that include strokes.

              Why? Often, a sketch or a line drawing needs to be converted to vector artwork with the resulting paths consisting of all matching-width strokes. Image Trace enables this recognition of thin black regions of your image and generates corresponding strokes apart from the standard filled objects.

              Stroke pixel width definition gives you some control over which long thin black regions are converted to strokes and which are not. In general a long black region needs to be quite thin to be converted to a stroke, at least for most of its length and it needs to be at least twice as long as it is wide. All output strokes are given the same weight, easily changed after expanding the tracing.

            Strokes and fills in Image Trace

            Part 5: Curve Fitting

            Once Image Trace completes the color palette and pixel assignment tasks, the groups of pixels are ready for conversion to filled shapes. Jagged pixel boundaries must be replaced with smooth Bezier-curve paths. Because it is often ambiguous as to what the intended or most aesthetic curve would be along a pixelated edge, the advanced options in the Image Trace panel offer some controls over curve fitting.

            1. The Paths slider
              The Paths slider in Image Trace

              The Paths slider controls how closely the Bezier paths hug the pixel boundary; it controls how well the curve fits. When the slider is to the left the fit is looser, and to the right the fit is tighter. The number values from 1 to 100 only indicate more or less, not any particular value.

              If you’re interested in the number of resulting curves and control points, a looser fit has fewer segments and control points. A tighter fit has more. Also, when the fit is loose, the curve will generally be smoother because tiny irregularities in the pixel boundary are overlooked.

            2. The Corners slider

              The Corners slider controls how likely it is that a sharp bend will be turned into a corner point. Two characteristics make a sharp bend more likely to result in a corner. The Corners slider in Image Trace
              One, the sharpness of the angle between the two curves coming in. Two, whether there are just a small number of pixels over which the bend occurs.

              The slider controls the threshold for these two together. When the slider is to the right, the more corner points you’ll get in your traced output. And as with the path slider, the corners slider values (1 to 100) are for mnemonic purposes only.

               

            3. The Snap to Lines checkbox
              This checkbox is usually off, but can be turned on if you want to replace gentle curves with lines. It will also cause a line near to 0 or 90 degrees to be snapped to absolute 0 or 90 degrees. This is useful for geometric artwork or if shapes in your source image are slightly rotated.

            4. Abutting versus Overlapping paths
              This is a new option for Image Trace that was not present in the old Live Trace tool: the ability to choose results that consist of overlapping paths as opposed to abutting paths. Abutting paths are fills that do not overlap at all — the edge of one fill is exactly the same as the edge of its neighboring fill. If you move one fill slightly you will create a gap and see the white background underneath. With overlapping paths, each fill slightly overlaps its neighbor. And if one fill is completely inside another, there is no hole cut out of the larger fill.

              In the advanced section of the Live Trace panel choose abutting paths or overlapping paths next to the Method label. You can think of abutting paths as cutout shapes and overlapping paths as stacked shapes.

            5. Here are some comparisons between overlapping and abutting paths:

            1. Anti-aliasing artifacts are not a factor with overlapping paths. With abutting paths sometimes there is a faint lighter color visible on the boundary between shapes. This is because each of the two shapes is anti-aliased against the (usually) white background, producing pixels that are slightly lighter than either of the colors of the abutting shapes. With overlapping paths this does not occur.
            2. With overlapping paths there are no holes in the resulting fills. Abutting shapes create cutouts.
              For example, if your image includes text, you may wish to select and move a fill for the letter “A” without leaving a hole in the shape beneath. Choose overlapping in this case.
            3. The number of resulting paths and control points is about the same for either option with one exception. If the traced result has a large number of fills that are concentric shapes, each inside the other like a target, then the overlapping method will produce fewer paths.
            4. Occasionally with the overlapping option there are small cracks between adjacent fills. These usually show up as tiny flecks of white and are usually only visible when zoomed in. They are more likely occur with complex artwork when the paths slider is either very far to the left or very far to the right. Cracks can be fixed by expanding your artwork and manually editing the overlapping paths.

            Part 6: Wrapping up
            Thanks for taking the time to explore the new Image Trace in Adobe Illustrator. For additional information, please check out these related videos on Adobe TV.

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