c9e88a08f8
Updated INSTALL doc to mention FriBiDi (should've done that in 0.9.21). Updated EXTENDING doc to mention that non-transparent Starters are ok (ditto).
331 lines
15 KiB
HTML
331 lines
15 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html><head><title>Tux Paint Advanced Stamps HOWTO</title>
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<center>
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<h1><img src="images/tuxpaint-title.png" width=220 height=219
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alt="Tux Paint"><br>
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version
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0.9.22
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<br>
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Advanced Stamps HOWTO</h1>
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<p>Copyright 2006-2008 by Albert Cahalan for the Tux Paint project<br>
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New Breed Software</p>
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<p><a href="mailto:albert@users.sf.net">albert@users.sf.net</a><br>
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<a href="http://www.tuxpaint.org/">http://www.tuxpaint.org/</a></p>
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<p>March 8, 2006 - July 1, 2009</p>
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</center>
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<h2>About this HOWTO</h2>
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<blockquote>
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<p>This HOWTO assumes that you want to make an excellent Tux Paint
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stamp, in PNG bitmapped format, from a JPEG image (e.g., a digital
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photograph). There are easier and faster methods that
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produce lower quality.</p>
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<p>This HOWTO assumes you are dealing with normal opaque objects. Dealing
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with semi-transparent objects (fire, moving fan blade, kid's baloon)
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or light-giving objects (fire, lightbulb, sun) is best done with custom
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software. Images with perfect solid-color backgrounds are also best done
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with custom software, but are not troublesome to do as follows.</p>
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</blockquote>
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<h2>Image choice is crucial</h2>
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<blockquote>
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<h3>License</h3>
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<blockquote>
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<p>If you wish to submit artwork to the Tux Paint developers for
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consideration for inclusion in the official project, or if you wish to
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release your own copy of Tux Paint, bundled with your own graphics,
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you need an image that is compatible with the GNU
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<a href="../COPYING.txt">General Public License</a> used by
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Tux Paint.</p>
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<p>Images produced by the US government are Public Domain, but be aware
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that the US government sometimes uses other images on the web.
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<a href="http://images.google.com/">Google image</a> queries including
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either <code>site:gov</code> or <code>site:mil</code> will supply many
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suitable images. (Note: the *.mil sites include non-military content,
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too!)</p>
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Your own images can be placed in the Public Domain by declaring it
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so. (Hire a lawyer if you feel the need for legal advice.)</p>
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<p>For personal use, any image you can legitimately modify and use
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for your own personal use should be fine.</p>
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</blockquote>
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<h3>Image Size and Orientation:</h3>
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<blockquote>
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<p>You need an image that has a useful orientation. Perspective is
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an enemy. Images that show an object from the corner are difficult to
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fit into a nice drawing. As a general rule, telephoto side views are
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the best. The impossible ideal is that, for example, two wheels of a
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car are perfectly hidden behind the other two.</p>
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<p>Rotating an image can make it blurry, especially if you only rotate by
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a few degrees. Images that don't need rotation are best, images that need
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lots of rotation (30 to 60 degrees) are next best, and images that need
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just a few degrees are worst. Rotation will also make an image darker
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because most image editing software is very bad about gamma handling.
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(Rotation is only legitimate for gamma=1.0 images.)</p>
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<p>Very large images are more forgiving of mistakes, and thus easier to
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work with. Choose an image with an object that is over 1000 pixels
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across if you can. You can shrink this later to hide your mistakes.</p>
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<p>Be sure that the image is not too grainy, dim, or washed out.</p>
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<p>Pay attention to feet and wheels. If they are buried in something,
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you will need to draw new ones. If only one is buried, you might be
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able to copy the other one as a replacement.</p>
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</blockquote>
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</blockquote>
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<h2>Prepare the image:</h2>
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<blockquote>
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<p>First of all, be sure to avoid re-saving the image as a JPEG. This causes
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quality loss. There is a special tool called
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<a href="http://gnuwin32.sourceforge.net/packages/jpeg.htm">jpegtran</a>
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that lets you crop an image without the normal quality loss. If you want a
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GUI for it, use
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<a href="http://astron.berkeley.edu/~mperrin/software/ljcrop/">ljcrop</a>.
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Otherwise, use it like this:</p>
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<blockquote>
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<p><code>jpegtran -trim -copy none -crop 512x1728+160+128 < src.jpg
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> cropped.jpg</code></p>
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</blockquote>
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<p>Bring that image up in your image editor. If you didn't crop it yet,
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you may find that your image editor is very slow. Rotate and crop the
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image as needed. Save the image — choose whatever native format
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supports layers, masks, alpha, etc. <a href="http://www.gimp.org/">GIMP</a>
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users should choose "XCF", and Adobe Photoshop users should choose "PSD",
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for example.</p>
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<p>If you have rotated or cropped the image in your image editor, flatten
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it now. You need to have just one RGB layer <i>without mask or
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alpha</i>.</p>
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<p>Open the layers dialog box. Replicate the one layer several times.
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From top to bottom you will need something like this:</p>
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<ol>
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<li>unmodified image (write-protect this if you can)
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<li>an image you will modify — the "WIP" layer
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<li>solid green (write-protect this if you can)
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<li>solid magenta (write-protect this if you can)
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<li>unmodified image (write-protect this if you can)
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</ol>
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<p>Give the WIP layer a rough initial mask. You might start with a
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selection, or by using the grayscale value of the WIP layer. You might
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invert the mask.</p>
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<p><b>Warning:</b> once you have the mask, you may not rotate or
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scale the image normally. This would cause data loss. You will be
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given special scaling instructions later.</p>
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</blockquote>
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<h2>Prepare the mask:</h2>
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<blockquote>
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<p>Get used to doing Ctrl-click and Alt-click on the thumbnail images in the
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layers dialog. You will need this to control what you are looking at and
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what you are editing. Sometimes you will be editing things you can't see.
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For example, you might edit the mask of the WIP layer while looking at the
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unmodified image. Pay attention so you don't screw up. Always verify that
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you are editing the right thing.</p>
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<p>Set an unmodified image as what you will view (the top one is easiest).
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Set the WIP mask as what you will edit. At some point, perhaps not
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immediately, you should magnify the image to about 400% (each pixel of
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the image is seen and edited as a 4x4 block of pixels on your screen).</p>
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<p>Select parts of the image that need to be 100% opaque or 0% opaque.
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If you can select the object or background somewhat accurately by
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color, do so. As needed to avoid selecting any pixels that should be
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partially opaque (generally at the edge of the object) you should
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grow, shrink, and invert the selection.</p>
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<p>Fill the 100% opaque areas with white, and the 0% opaque areas with
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black. This is most easily done by drag-and-drop from the
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foreground/background color indicator. You should not see anything happen,
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because you are viewing the unmodified image layer while editing the mask
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of the WIP layer. Large changes might be noticable in the thumbnail.</p>
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<p>Now you must be zoomed in.</p>
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<p>Check your work. Hide the top unmodified image layer. Display just the
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mask, which should be a white object on a black background (probably
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with unedited grey at the edge). Now display the WIP layer normally, so
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that the mask is active. This should show your object over top of the
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next highest enabled layer, which should be green or magenta as needed
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for maximum contrast. You might wish to flip back and forth between
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those backgrounds by repeatedly clicking to enable/disable the green
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layer. Fix any obvious and easy problems by editing the mask while
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viewing the mask.</p>
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<p>Go back to viewing the top unmodified layer while editing the WIP mask.
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Set your drawing tool the paintbrush. For the brush, choose a small fuzzy
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circle. The 5x5 size is good for most uses.</p>
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<p>With a steady hand, trace around the image. Use black around the outside,
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and white around the inside. Avoid making more than one pass without
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switching colors (and thus sides).</p>
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<p>Flip views a bit, checking to see that the mask is working well. When
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the WIP layer is composited over the green or magenta, you should see a
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tiny bit of the original background as an ugly fringe around the edge.
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If this fringe is missing, then you made the object mask too small.
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The fringe consists of pixels that are neither 100% object nor 0% object.
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For them, the mask should be neither 100% nor 0%. The fringe gets removed
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soon.</p>
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<p>View and edit the mask. Select by color, choosing either black or white.
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Most likely you will see unselected specks that are not quite the expected
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color. Invert the selection, then paint these away using the pencil tool.
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Do this operation for both white and black.</p>
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</blockquote>
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<h2>Replace the fringe and junk pixels:</h2>
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<blockquote>
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<p>Still viewing the mask, select by color. Choose black. Shrink the
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selection by several pixels, being sure to NOT shrink from the edges of
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the mask (the shrink helps you avoid and recover from mistakes).</p>
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<p>Now disable the mask. View and edit the unmasked WIP layer. Using the
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color picker tool, choose a color that is average for the object.
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Drag-and-drop this color into the selection, thus removing most of the
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non-object pixels.</p>
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<p>This solid color will compress well and will help prevent ugly color
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fringes when Tux Paint scales the image down. If the edge of the
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object has multiple colors that are very different, you should split up
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your selection so that you can color the nearby background to be
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similar.</p>
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<p>Now you will paint away the existing edge fringe. Be sure that you are
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editing and viewing the WIP image. Frequent layer visibility changes will
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help you to see what you are doing. You are likely to use all of:</p>
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<ul>
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<li>composited over green (mask enabled)
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<li>composited over magenta (mask enabled)
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<li>original (the top or bottom layer)
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<li>composited over the original (mask enabled)
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<li>raw WIP layer (mask DISABLED)
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</ul>
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<p>To reduce accidents, you may wish to select only those pixels that are
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not grey in the mask. (Select by color from the mask, choose black, add
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mode, choose white, invert. Alternately: Select all, select by color from
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the mask, subtract mode, choose black, choose white.) If you do this,
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you'll probably want to expand the selection a bit and/or hide the
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"crawling ants" line that marks the selection.</p>
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<p>Use the clone tool and the brush tool. Vary the opacity as needed.
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Use small round brushes mostly, perhaps 3x3 or 5x5, fuzzy or not.
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(It is generally nice to pair up fuzzy brushes with 100% opacity and
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non-fuzzy brushes with about 70% opacity.) Unusual drawing modes can be
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helpful with semi-transparent objects.</p>
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<p>The goal is to remove the edge fringe, both inside and outside of
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the object. The inside fringe, visible when the object is composited
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over magenta or green, must be removed for obvious reasons. The
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outside fringe must also be removed because it will become visible
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when the image is scaled down. As an example, consider a 2x2 region of
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pixels at the edge of a sharp-edged object. The left half is black
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and 0% opaque. The right half is white and 100% opaque. That is, we
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have a white object on a black background. When Tux Paint scales this
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to 50% (a 1x1 pixel area), the result will be a grey 50% opaque pixel.
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The correct result would be a white 50% opaque pixel. To get this
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result, we would paint away the black pixels. They matter, despite
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being 0% opaque.</p>
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<p>Tux Paint can scale images down by a very large factor, so it is
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important to extend the edge of your object outward by a great deal.
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Right at the edge of your object, you should be very accurate about this.
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As you go outward away from the object, you can get a bit sloppy. It is
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reasonable to paint outward by a dozen pixels or more. The farther you go,
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the more Tux Paint can scale down without creating ugly color fringes.
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For areas that are more than a few pixels away from the object edge, you
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should use the pencil tool (or sloppy select with drag-and-drop color) to
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ensure that the result will compress well.</p>
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</blockquote>
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<h2>Save the image for Tux Paint</h2>
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<blockquote>
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<p>It is very easy to ruin your hard work. Image editors can silently
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destroy pixels in 0% opaque areas. The conditions under which this
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happens may vary from version to version. If you are very trusting,
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you can try saving your image directly as a PNG. Be sure to read it
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back in again to verify that the 0% opaque areas didn't turn black or
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white, which would create fringes when Tux Paint scales the image down.
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If you need to scale your image to save space (and hide your mistakes), you
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are almost certain to destroy all the 0% opaque areas. So here is a better
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way...</p>
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<h3>A Safer Way to Save:</h3>
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<blockquote>
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<p>Drag the mask from the layers dialog to the unused portion of
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the toolbar (right after the last drawing tool). This will create a
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new image consisting of one layer that contains the mask data. Scale
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this as desired, remembering the settings you use. Often you should
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start with an image that is about 700 to 1500 pixels across, and end
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up with one that is 300 to 400.</p>
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<p>Save the mask image as a NetPBM portable greymap ("<code>.pgm</code>")
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file. (If you are using an old release of The GIMP, you might need
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to convert the image to greyscale before you can save it.) Choose the
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more compact "RAW PGM" format. (The second character of the file
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should be the ASCII digit "5", hex byte 0x35.)</p>
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<p>You may close the mask image.</p>
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<p>Going back to the multi-layer image, now select the WIP layer. As you
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did with the mask, drag this from the layers dialog to the toolbar. You
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should get a single-layer image of your WIP data. If the mask came along
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too, get rid of it. You should be seeing the object and the painted-away
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surroundings, without any mask thumbnail in the layers dialog. If you
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scaled the mask, then scale this image in exactly the same way. Save
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this image as a NetPBM portable pixmap ("<code>.ppm</code>") file.
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(Note: ppm, not pgm.) (If you choose the RAW PPM format, the
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second byte of the file should be the ASCII digit "6", hex byte 0x36.)</p>
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<p>Now you need to merge the two files into one. Do that with the
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<a href="http://netpbm.sourceforge.net/">pnmtopng</a> command, like
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this:</p>
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<blockquote><p><code>
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pnmtopng -force -compression 9 -alpha mask.pgm fg.ppm >
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final-stamp.png
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</code></p></blockquote>
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</blockquote>
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</blockquote>
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</body></html>
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