ImageMagick v6 Examples --
Advanced Techniques

Index
ImageMagick Examples Preface and Index

	3D Bullets from Shapes		Using a script to generate huge numbers of images Color tinting and shaping a 3-D greyscale shade image
	Making Logos 3D		Using transparent overlays to tint the basic shaped image
	Better 3D Logo Generation		Using an 'Overlay' alpha compose to tint the shape Also adding semi-transparent shadows.
	Jigsaw Pieces		Cutting out and enhancing a odd shaped piece from a photo
	"Gel" Effects		Adjusting the size, brightness, and sharpness of the highlight Lighting and Darkening using 'Screen' and 'Multiply' compose
	"Aqua" Effects		Using 'curves' to adjust the highlights.
	Tilable Stars and Comets		Randomized Points. "My God! It's full of stars! -- 2001, A Space Odessy"
	Radial Flares

This page provides very large examples where we use multiple techniques to produce some compound image manipulation effects, beyond the basic image operations of IM. The major techniques are summarized in the index above.

While many techniques are provided on other pages, such as creating font templates, fancy labeling images, and using masks, these pages show how you can combine those techniques together to produce a more complex effect.

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3-D Bullets from Shapes -- scripted approach

Their are a lot of 'bullet' images available on the web for your web listings. But you can generate your own 3d objects, and allowing you to make your whole web site conform to a particular style that ties it all together.

One of the best ways to do that is to create a 'generate' script that lets you automatically generate a whole range of buttons and shapes of a particular style, but using any color you require. This is one such, very simple script.

Here we use the "-shade" option to generate 3d looking objects from a plain shaped transparency. The shape has only straight on/off transparency, which is carefully preserved, allowing it to be used as transparent GIF images for general use on web pages.

The resulting grayscale 'shaded' image is then coloured using the "-tint" operator, to set the mid-tone greys of the image, while leaving the more extreme black and white shadings alone.

After that the original shape of the image provided is re-added to the colored result. As a bonus if the input image had only a Boolean transparency the result also has a Boolean transparency appropriate for a GIF format image.

Note that the input image is only read in once by the above script. This allows you to also use the script in a pipeline of commands using '-' as the input and output filenames (with perhaps an IM image format setting). This can be important when writing your own IM scripts.

The above command was written into a very simple shell script called "create_bullet", and the following commands were executed, to generate a whole range of symbol images in many different colors. Only the shape or transparency of the source image is used in generating the bullets, as such any shape can be used. Pick your own shape that is unique to your website. Also note that GIF or PNG can be used, with out without Boolean transparency, the command makes no distinction.

If you do use a larger image than that shown here, you may also like to increase the amount of blurring that is applied before the shade operation. Otherwise you may find only the areas close to the edge of the images will be rounded. Also it may be better to blur multiple times rather than use a big blur value (to increase the speed of the blurring).

Of course if you make some improvements or have other ideas, please let me know, so we can share them with others.

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Making Logos 3-D

In this example we have a flat colored logo, with a difficult shape, which we what to image process to give it a distinct 3-D look. To do this we use the logo to generate highlights and shadows, and convert them into transparencies to overlay on the original image. It uses a lot different techniques from all of the example pages to achieve this effect, step by step.

This example makes heavy use of images generated by the Shade Operator, in particular the special Dawn Highlight images that shade create from a shape. It also make heavy use of the various Alpha Compositing methods. I suggest you become familiar with these image operators before proceeding, or look them up when you wish to understand better what is going on.

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Before we can start however we will need a simple logo to apply our technique to, and its mask....

Lets first create a shape for the color background of logo example...

convert -size 170x100 xc:black \ -fill white -draw 'circle 50,50 13,50' \ -draw 'circle 120,50 157,50' \ -draw 'rectangle 50,13 120,87' \ -fill black -draw 'circle 50,50 25,50' \ -draw 'circle 120,50 145,50' \ -draw 'rectangle 50,25 120,75' \ -fill white -draw 'circle 60,50 40,50' \ -draw 'circle 110,50 130,50' \ -draw 'rectangle 60,30 110,70' \ -gaussian 1x1 +matte logo_mask.png

Now we use our mask to cut out the solid color of our logo, and add some text to generate a plain, solid color logo.

convert logo_mask.png +clone +matte -compose CopyOpacity -composite \ -fill red -colorize 100% \ -font Candice -pointsize 36 -fill white -stroke black \ -gravity Center -annotate 0 "Ant" \ logo.png

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Now that we have our very plain flat-looking 2 dimensional logo, lets see if we can add highlights to turn it into a 3 dimensional looking logo.

As part of our logo creating we create a transparency 'mask'. If you have an existing logo, you will need to extract the image mask for the next step, but that is straight forward.

To start the process we create appropriate light and dark areas to be added to the flat logo. The shade operation is used to do this.

If we apply shade to the image mask of our logo directly, as is, you will get a strongly beveled image, such as in the Beveled Font Example.

By blurring the mask first, the beveled edges generated by shade will be smoothed off and the sharp corners have a slightly buffed or sanded look.

By using blurring three times, the final logo will appear even more rounded. And that is what I want in this example.

convert logo_mask.png -blur 0x4 -blur 0x4 -blur 0x4 \ +matte logo_spread.png

Now we run the rounded mask though shade, to get what this image would look like if a object with this shape was placed in a spotlight.

convert logo_spread.png -shade 110x0 -normalize logo_light.png

Do it again, but this time from the opposite side, so as to define the darkened areas of out logo.

convert logo_spread.png -shade 110x180 -normalize logo_dark.png Note that the result is an inverse of the dark shading in the final the image. That will be corrected when you use this to create the shade mask for the logo.

Now we can combine the two results together into an single overlay of highlights and shading. This is achieved by using the above image as a mask of a pure white image (for highlights) or pure black (for shadow effects). See Colored Masks for the many ways in which these semi-transparent overlay images can be created.

These are then overlaid together to form a single overlay image, though we could also apply the two mask images separately if you want.

convert \( logo_light.png -negate \ -background white -channel A -combine +channel \) \ \( logo_dark.png -negate \ -background black -channel A -combine +channel \) \ -compose Over -composite logo_lighting.png

The result as you can see looks like a semi-transparent 3 dimensional ripple of our original logo, that extends well beyond its boundaries.

To add these light and dark areas to our logo, we only need to overlay it onto the original logo image, but we also need to limit it to within the boundaries of the original logo. A job for another special compose operator, 'ATop'

convert logo.png logo_lighting.png -compose ATop -composite logo_3D.png   And hey presto, our plain, solid color logo now looks 3 dimensional!

This result is good, but it needs just a little bit extra to complete the job. Something to make it standout from the page. For that we want to add a soft shadow to the image, but not just a simple black shadow, lets make a very dark blue shadow to match the background of this page.

convert logo_3D.png -channel A -blur 0x6 +channel \ -fill navy -colorize 100% logo_shadow.png

This uses a similar (though different) masking technique that we used previously. See Colored Masks.

Now we can overlay our shadow 'under' our logo, using the 'Dst_Over" composition operator, with a slight offset. As the shadow image is offset I also need to add some extra space. That combined with the gravity setting (which I did not turn off) also sets the offset of the shadow to the original image.

convert logo_3D.png -background none -gravity SouthEast -splice 6x6+0+0 \ logo_shadow.png -compose Dst_Over -composite logo_final.png And that completes our 3D looking logo, complete with shading and shadows.

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If you examine the above commands carefully, you will find the only time I use actual image dimensions is for the initial creation of the logo. Everywhere else I used previously created images to generate working canvases, without needing to ask about the original images size. By doing this the above commands can be used for any sized logo, not just this specific logo.

The only other variables used is the sigma amount for the blur operation, which determines how rounded the logo looks, the offset for the shadow, and the color of the shadow to match the background the logo will be used on (this page in this case).

The whole example turned out far better than I originally hoped, and as you can see there are no color or shape limitations to the technique. The above could be easily be scripted into a general, "convert Image to 3-D' script, and in fact this is how some cartoon characters were given basic 3-D look.

I suggest however that you continue into the next set of examples, where we use some of the more complex methods to achieve the same result, only faster, with fewer commands.

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Better 3-D Logo Generation

While the above shows a verbose step-by-step approach to developing a sequence of operations to achieve a specific target. However as your knowledge on Image Manipulations improve, so does the techniques and methods employed to achieve that goal.

ImageMagick itself is changing and improving, adding new operations, and fixing bugs and problems with existing commands.

In this section I again generate a 3D logo from the flat color starting image, but this time using some specific ImageMagick improvements which make the task a lot simpler and easier.

Lets start by again showing the start logo we will be giving a 3D look. This is exactly as above, to produce the sample logo.

convert -size 170x100 xc:black \ -fill white -draw 'circle 40,40 3,40' \ -draw 'circle 110,40 147,40' \ -draw 'rectangle 40,3 110,77' \ -fill black -draw 'circle 40,40 15,40' \ -draw 'circle 110,40 135,40' \ -draw 'rectangle 40,15 110,65' \ -fill white -draw 'circle 50,40 30,40' \ -draw 'circle 100,40 120,40' \ -draw 'rectangle 50,20 100,60' \ -gaussian 1x1 +matte ant_mask.png convert ant_mask.png -fill red -draw 'color 0,0 reset' \ ant_mask.png +matte -compose CopyOpacity -composite \ -font Candice -pointsize 36 -fill white -stroke black \ -gravity Center -annotate 0 "Ant" \ ant.png

I still use a mask for generating the logo, as this is a good way of erasing the area between the central oval and the outer ring of the logo.

Now lets give it a 3D-look, by using Overlay Highlighting techniques.

convert ant.png -fx A +matte -blur 0x6 -shade 110x30 -normalize \ ant.png -compose Overlay -composite \ ant.png -matte -compose Dst_In -composite \ ant_3D.png

Adding shadows is also easier thanks to the new Shadow Generation operator provided by IM.

convert ant_3D.png \( +clone -background navy -shadow 80x4+6+6 \) +swap \ -background none -layers merge +repage ant_3D_shadowed.png

The above techniques as you can see is far simpler than the convoluted method above, but on the other hand the result is not quite as good as the previous method, producing much less distinct highlight effects.

Just for fun lets finish by overlay our logo on a 'rough paper' like background. A huge number of other background canvases can also be created, see Background Examples for a collection of such examples.

convert ant_3D_shadowed.png \ \( +clone +repage +matte -fx 'rand()' -shade 120x30 \ -fill grey70 -colorize 60 \ -fill lavender -tint 100 \) -insert 0 \ -flatten ant_3D_bg.jpg

If you have any other improvements, please let me know.

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Jigsaw Pieces

One of the most interesting things I have been asked to help with was to cut out and enhance a odd shaped 'jigsaw' piece from a larger picture. Actually Theo van Hoesel, also known as "Mr Jigsaw", wanted to generate a lot of separate pieces, at lots of different rotations. The following was developed from our discussion for just one piece, but with the right set of templates, any pattern of pieces can be generated.

To the right is a thumbnail linked to a 800x600 image of a photo of the Holocaust Memorial, Berlin, Germany. I took this photo during on my European trip in April 2006. It looks like a great image to make a really hard jigsaw puzzle from. And below it is a template image of the jigsaw piece I will be extracting from the above image. It was part of a set of such images. The full set of jigsaw pieces contains 192 such masks, in a 16 by 12 array, including edges and corners. This specific jigsaw piece is a 100x100 pixel mask, and designed to be used at a +365+96 offset on an 800x600 pixel image. These figures are only important if you have a large set of different pieces that will fit together. If you don't plan to do this then of course you can use any offset you like.

I myself have collected a number of such jigsaw sets, which can let me make a jigsaw of any image. And this is what Theo van Hoesel, is actually doing on his website.

If you are making a actual jigsaw puzzle then the offset information is very important, as it identifies the location and placement of that piece from the original image. As such I will try to preserve this information. Note that offsets for masks could in some cases be negative, due to the extra padding around the shape, so you may need to test and adjust image commands to handle this situation.

The extra padding itself will allow you to easily rotate, add thickness and shadow effects to the final image, without needing to chnage the size or offset of the cutout jigsaw piece.

First however lets convert this template into an outline. convert jigsaw_tmpl.png -edge .5 -blur 0x.5 jigsaw_edge.png

I can then overlay this onto the image to get a rough idea as to what is going to be cutout to form the jigsaw piece.

convert holocaust_md.jpg \ \( jigsaw_edge.png -negate \) -geometry +365+96 \ -compose multiply -composite \ -crop 100x100+365+96 +repage jigsaw_outline.png

Normally this is not done when generating a jigsaw, but is useful to do when the position of the piece is not important (as it isn't part of a larger puzzle). If so you can adjust the offset to select better content for that jigsaw piece.

Due to the way "-edge" works the jigsaw outline generated above is inside the masked (white) area masking image. This can be important if you like to make use of this outline later.

Okay we have a jigsaw shape, and a offset for the piece to cut out. so lets cut it out and rotate it too.

convert holocaust_md.jpg \ -crop 100x100+365+96\! -background none -flatten +repage \ \( jigsaw_tmpl.png +matte \) -compose CopyOpacity -composite \ -rotate -20 -gravity center -crop 100x100+0+0 +repage \ jigsaw_cutout.png

Note that we cropped the source image to the area covered by out template shape. We will not need the area outside the mask, and removing it early will speed up the image processing.

Also note the special use of a viewport crop, followed by "-flatten". This method of cropping will ensure that we will be guaranteed a 100x100 pixel image from which to 'cutout' the template, even when using masks of edge or corner pieces, and also handle a negative offset for pieces on or near the top, or left, edges of the image.

The rotate is also performed at this point as most enhancements will add effects basied on a specific direction. The result of that rotate is also center cropped as this operator, normally expands the resulting image size, depending on the rotation angle used, and we don't want it to do that.

The first enhancement is to give the pieces a slightly beveled, or rounded, highlight around the edges. This is as per Shade Highlight Overlays, which allows fine control 94 separate factors) of way the highlight is produced.

convert jigsaw_cutout.png \ \( +clone -channel A -separate +channel -negate \ -background black -virtual-pixel background \ -blur 0x2 -shade 120x21.78 -contrast-stretch 0% \ +sigmoidal-contrast 7x50% -fill grey50 -colorize 10% \ +clone +swap -compose overlay -composite \) \ -compose In -composite jigsaw_bevel.png

In a real jigsaw this bevel is a result of machine press cutting the jigsaw pieces. It also gves the pices a slight dent, so if the pieces are fitted back together you can still see the impression of the cuts.

Now lets add some thickness to the piece. This is the best and quickest way I have found, though I don't consird it a very good technique. If you can find something better, then please let me know.

convert jigsaw_bevel.png \ \( +clone -fill DarkSlateGrey -colorize 100% -repage +0+1 \) \ \( +clone -repage +1+2 \) \( +clone -repage +1+3 \) \ \( +clone -repage +2+4 \) \( +clone -repage +2+5 \) \ -background none -compose DstOver -flatten \ jigsaw_thickness.png

And finally how about some shadow.

convert jigsaw_thickness.png \ \( +clone -background Black -shadow 50x3+4+4 \) \ -background none -compose DstOver -flatten \ jigsaw_shadow.png

All the above commands can be easily saved into a single shell script, and I have done this for my own use.

The script "jigsaw" will take three image parameters: source photo, template, and destination, as well as numerious options to enable the various enhancements shown above. It does not need to use a jigsaw shape either. Any mask template could be used to cut out parts of images, with appropriate added effects.

The biggest difference between the above, and my script version, is that by default, the script keeps the final image as small as possible, while keeping track of offset of the cutout image. By preserving this offset position you can to use a simple "-mosaic" or "-flatten" to overlay multiple pieces back together to produce interesting effects (see last example below).

Here is just a few examples of using this script, in a number of ways.

The last image is the beginning of a possible jigsaw thumbnail style...

It takes a corner jigsaw piece, and with some scaling and expansion converts the mask, into a full sized image template mask. This is then used to not only cut out the corner piece from an existing thumbnail, but also is negated to produce the rest of the image as well. Overlaying these two images then produces quite a fancy looking jigsaw thumbnail.

Note the use of a '-d +20+15' in the options to the piece creation. This displaces the 'page offset' of the generated PNG image by a small amount relative to its original position in the image, producing the result shown, simply and easily. See the script itself for the other options available.

As page offsets generated can be negative, and could contain an optional soft shadow effect, it is recommended that only PNG images be used for extracted pieces. GIF images can not handle negative page offsets, or shadow effects, nor does it produce a smooth looking anti-aliased edges when transparency is involved. Generally you should avoid GIF (and JPEG) images for all but your final image. For more information see Common Image Formats examples page.

You are not limited to jigsaw puzzle templates, but any shaped mask can be used with any image. Let me know what you come up with.

I am not quite finished with the development of the "jigsaw" script, as I would like some better controls for the highlighting, thickness and shadow effects, and posibly a 'negate mask' option. It is however basically a complete working program you are free to use. Give me a link back if you use it for a web page :-)

For those with some PerlMagick API skill, try taking the above script and converting it to PerlMagick for speed, then submitting it to me so that everyone else can also use it, and know just how good you are at using IM. Further suggestions and ideas are always welcome.

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"Gel" Effects

The 3-D shadings used above is only the start of what you can do with highlight and shaded effects. By doing various histogram adjustments to the output of "-shade" an enormous range of possibilities is available.

One such effect you can reproduce is known as a 'Gel' effect, such as often see in "Photoshop how-to web sites (Google for "Gel Effects Tutorial"). First lets create the shape we need. This could be a pre-prepared image or extracted from a 'Dings' font, like we did with the 3D bullet shaped "heart" above.

In this case lets use a simple oval shape for a button...

convert -size 100x60 xc:none \ -fill red -draw 'circle 25,30 10,30' \ -draw 'circle 75,30 90,30' \ -draw 'rectangle 25,15 75,45' \ gel_shape.png

Now lets add the sharp 'Gel' highlight to the colored shape, using a highly modified blurred shade operation...

convert gel_shape.png \ \( +clone -fx A +matte -blur 0x12 -shade 110x0 -normalize \ -sigmoidal-contrast 16,60% -evaluate multiply .5 \ -roll +5+10 +clone -compose Screen -composite \) \ -compose In -composite gel_highlight.png

We applied "-shade" to a copy of the transparency (matte) channel after blurring it to round it off. A horizontal lighting used, so we get a grey for the highlight and black for anything else which was unaffected.

This highlighting greyscale was then adjusted using the "-sigmoidal-contrast" operator to reduce the size the highlighted area (the '60%' threshold level) and sharpen its edges (using a very high '16' exponential factor). With such a high exponential value, the operator is essentially acting as a 'fuzzy' "-threshold" operator. For more information on this smooth contrast/threshold function see Sigmoidal Non-linearity Contrast.

And finally the level of the highlight was set using a "-evaluate" convolution to multiply all the colors by the desired highlight level, before "-roll" is used to position it within the original shaped area.

Now as the highlight is a grey on black (black to remain unchanged) a 'Screen' alpha composition is used to lighten the non-black areas by the given grey level.

Now all that is left is to darken the borders a little...

convert gel_highlight.png \ \( +clone -alpha extract -blur 0x2 -shade 0x90 -normalize \ -blur 0x2 +level 60,100% -alpha On \) \ -compose Multiply -composite gel_border.png

Note that this time I used a vertically lit "-shade" for edge darkening, which makes the areas I want to preserve unchanged, a white color. As such after adjusting the greyscale using a Reversed Level Adjustment, and restoring the transparency saved by the Alpha Extract Method, I was then able to use a 'Multiply' alpha composition to darken the effected borders.

Lets finish of the oval 'Gel' button with some text and shadow effects...

convert gel_border.png \ -font Candice -pointsize 24 -fill white -stroke black \ -gravity Center -annotate 0 "Gel" -trim -repage 0x0+4+4 \ \( +clone -background navy -shadow 80x4+4+4 \) +swap \ -background none -flatten gel_button.png

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"Aqua" Effects

You can also adjust a full 3-D "-shade" (with a 30 degree lighting) tint to produce a "Aqua" water effect. For this however we need to do a histogram adjustment in a way that is similar to what you do with GUI graphical programs like "Gimp" and "Photoshop".

This time however instead of a logo or button, lets apply this effect to a curvy letter A.

convert -background none -fill DodgerBlue \ -font Candice -pointsize 72 label:A -trim +repage \ \( +clone -alpha extract -blur 0x8 -shade 110x30 -normalize \ -function polynomial 3.5,-5.05,2.05,0.3 -alpha On \) \ -compose HardLight -composite aqua_font.png WARNING: the above is incomplete (edges have not been darkened)

The critical part of the above effect is the Polynomial Function which is used for a Curves Adjustment of the image. It is this function that gives the overall effect, and the most difficult to determine.

However using techniques developed in Curves Adjustment, we create this function based on the location of the control points needed, is a similar way that you would do this in GUI programs such as "Gimp" and "Photoshop".

So first we need the control points, to define the overall look we want to achieve.

• First we need to set appropriate black and white levels for the shadow and highlights of our image. That a black control point of 30% and white set to 80%. This produces control points of '0,30' and '100,80'.

• We also need to ensure that any parts of the image we do not want changed becomes a perfect grey. Now as a 30 degree azimuth "-shade" transform produces a perfect grey (50% grey) for unchanged areas. This needs to be preserved with a '50,50' control point.

• That leaves one final control point needed to produce our 'aqua' effect, specifically adjust 80% grey to 50% (EG: 80,50). Think of this as the 'aqua effect magic'.

Now lets use a IM support shell script called "im_fx_curves" to convert these four control points (using grey level percentages) into a equation that fits these point, and thus a list of polynomial coefficents.

This script uses the "gnuplot" program to do the work (and also generated the above graph). And from this you cans see the coefficients we used in the above example.

So lets repeat this example, but also add a slight darkening of the edges just as we did in 'Gel' effects above, so as to define the shape a little better.

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Tilable Stars and Comets

I wanted to make a tile of random star fields (with the stars of variable intensities) for various purposes. This was the result of my slowly improving attempts at this.

A random noise image is used to thin itself out generate a speckle pattern.

convert -size 100x100 xc: +noise Random -channel R -threshold 5% \ -negate -channel RG -separate +channel \ -compose multiply -composite speckles.gif

This pattern is the basis for glitter animation effects, but also the start point for other effects.

For example to make stars we need to modify its random 'speckle' pattern a bit more, so as to make things more realistic.

convert -size 100x100 xc: +noise Random -channel R -threshold 1% \ -negate -channel RG -separate +channel \ \( +clone \) -compose multiply -flatten \ -virtual-pixel tile -blur 0x.4 -contrast-stretch .8% \ stars.gif

Note that I multiply not only the speckle mask ('R' channel) but the star intensity image ('G channel) twice as well. This produces a squared fall-off in the pixel intensities so more darker stars are present than bright ones, just it is in the real night sky.

After this we enlarge the size of the stars based on their intensity by Blurring. This produces an effect similar to the stars burning onto a astronomers photographic plate, making it even more realistic. The larger the blur value the larger the effect. A final "-contrast-stretch" brings the results back to visibility.

By using two random noise images, (one for the mask, the other for the star color), we can generate randomly colored stars, instead of simple greyscale ones.

convert -size 100x100 xc: +noise Random -channel R -threshold 1% \ -negate -channel RG -separate +channel \ \( xc: +noise Random \) -compose multiply -flatten \ -virtual-pixel tile -blur 0x.4 -contrast-stretch .8% \ stars_colored.gif

This however may need more work, as we need to square the intensity of the colors directly instead of just simply multiplying them against a linear distribution. It does however work, and provides a starting point for further development.

Note the color does not have to be random but could easily come from some other image for the stars. For example the star color itself could be sourced from the image that will be used as the final background.

Now that I have a star-scape generator, I can simply use "-motion-blur" to create a field of falling stars!

convert -size 100x100 xc: +noise Random -channel R -threshold .4% \ -negate -channel RG -separate +channel \ \( +clone \) -compose multiply -flatten \ -virtual-pixel tile -blur 0x.4 -motion-blur 0x20+45 -normalize \ star_fall.gif

Of course we want less stars and less of a 'fall-off' in star intensities.

By Polar Distorting the image we can make the comets flying or spiraling into a point!

convert -size 250x100 xc: +noise Random -channel R -threshold .4% \ -negate -channel RG -separate +channel \ \( +clone \) -compose multiply -flatten \ -virtual-pixel Tile -background Black \ -blur 0x.6 -motion-blur 0x15-90 -normalize \ +distort Polar 0 +repage star_inward.gif convert -size 250x100 xc: +noise Random -channel R -threshold .4% \ -negate -channel RG -separate +channel \ \( +clone \) -compose multiply -flatten \ -virtual-pixel Tile -background Black \ -blur 0x.6 -motion-blur 0x15-60 -normalize \ +distort Polar 0 +repage star_spiral.gif

Here we motion blur the stars in six directions (in pairs) then merge them together to create a field of 'star bursts', such as you get in a glass lens.

convert -size 100x100 xc: +noise Random -channel R -threshold .2% \ -negate -channel RG -separate +channel \ \( +clone \) -compose multiply -flatten \ -virtual-pixel tile -blur 0x.3 \ \( -clone 0 -motion-blur 0x10+15 -motion-blur 0x10+195 \) \ \( -clone 0 -motion-blur 0x10+75 -motion-blur 0x10+255 \) \ \( -clone 0 -motion-blur 0x10-45 -motion-blur 0x10+135 \) \ -compose screen -background black -flatten -normalize \ star_field.gif

Note how the darker stars only generate a small dot and very little in the way of a 'star burst', while the bigger bright stars generate a very large 'star burst'.

Now if I can find a way to add a 'sinc()' type blurring so as to produce a flare 'ring' around the brightest stars as well, we will have a great star field generator. Add some plasma background and we can even generate fake astronomical photos of nebula and gas clouds.

By combining the above with a plasma glitter animation you can make set of stars that look like christmas decorations.

convert -size 100x100 xc: +noise Random -separate \ null: \ \( xc: +noise Random -separate -threshold 50% -negate \) \ -compose CopyOpacity -layers composite \ null: \ plasma:red-firebrick plasma:red-firebrick plasma:red-firebrick \ -compose Screen -layers composite \ null: \ \( xc: +noise Random -channel R -threshold .08% \ -negate -channel RG -separate +channel \ \( +clone \) -compose multiply -flatten \ -virtual-pixel tile -blur 0x.4 \ \( -clone 0 -motion-blur 0x15+90 -motion-blur 0x15-90 \) \ \( -clone 0 -motion-blur 0x15+30 -motion-blur 0x15-150 \) \ \( -clone 0 -motion-blur 0x15-30 -motion-blur 0x15+150 \) \ -compose screen -background black -flatten -normalize \) \ -compose multiply -layers composite \ -set delay 30 -loop 0 -layers Optimize stars_xmas.gif

The above techniques is only the start of what can be achieved. Using some simple animations techniques glitters, and random flares can be created which can be added to images. One simple example of this was provided in GIF animation examples, using a simple shell script "star_field" to generate the stars bursts.

What can you to with this star generator?

Challenge:

• Generate glitter rather than stars. The initial speckle field should be limited by a mask (say by multiplying). Both glitter and stars can then be overlaid onto an image using 'screen' composition.
• Use a masked 'speckle field' to generate star bursts. for overlaying. By masking the seeds rather than the complete star burst, means that 'rays' of the bursts can leave the masked area to overlay other parts of the image. That is rays are not just 'cutoff'.
• Create an animation of a random star bursts. This may require you to animate a single field of star bursts (perhaps with the rays rotating).
• By generating a few star burst animations, you can merge them together to form a series of overlapping star bursts from different locations.
• Find a single 'seed' point on the brightest part of the image by histogram stretching a thresholding. Then picking single pixels until one hits the masked area.
• Creating stars on the edge a flat shaded shape.

If you manage any of the above challenge, or use the star generator for some other purpose, please let me and the rest of the IM community know.

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Radial Flares

Experiments in generating radial flares.

Note that the width of the initial image before polar distorting, basically sets the number of rays that will be produced.

Note how I use "-write" to save intermedite images for display.

Here is another example using multiple overlays to achieve a different looking flare. Note the technique used to generating intermedite debugging and example images showing the steps involved.

The major problem with using polar distort for generating flar images is that the rays become wider with the radius, where really we want them to either remain a roughly constant width as they get dimmer, or at least thinner.

Ideas and pointers welcome

Color tinting can also be important in this type of image. For example here I Tint Mid-Tone Colors Blue. convert flare_2_final.png -fill SkyBlue -tint 100% flare_2_color.png

The percentage used for the "-tint" operation can also be used to adjust the intensity of the rays and flare ring, though it will nto changet the white core of the image bery much.