Колдовство imagemagick

IM and SVG handling

SVG Input Drivers: RSVG vs MSVG

SVG — Scalable Vector GraphicsMSVG-draw

Here I ‘draw’ a small, hand made, SVG image, «diagonal.svg» (contributed by the forum user penciledin), which creates
a rectangle with a simple diagonal gradient, on a white background.

However if you render this using the internal MSVG (the default if the RSVG
library is not present)…

  • Non-vertical Gradients (no conversion to new MVG gradient handling)
  • Text along a curved path
  • Text justification (as separate to gravity)

SVG settings


I have found that some SVG images will not scale. That is they have been
defined terms of ‘pixels’, rather than real-world lengths such as ‘points’,
‘inches’ or ‘millimeters’. As a consequence while the «» setting may change
the overall image size (in real-world units), the size of ‘pixels’ does not
change, and so the image itself does not change size. Such SVG images are
however quite rare.

Worse still a few SVG image use a mix of ‘pixel’ and ‘point’ measurments,
and unless the author did thid on purpose, you could get a real mess and you
try to use it as a different density that what the author intended. These
are fortunatally even rarer.

A simple fix is typically just change all ‘pixels’ units in the SVG to
‘points’, but it should not be done blindly, in case the use of ‘pixels’
was used on purpose.

Special Escape Characters in Text Arguments

Image Properties


Some system (like ubuntu) disable the use of the ‘@{file}’ escape using
security policy. Type to see what
policies and where they are set from are present on your system.


While backslash » is used by the «» »
method, the percent » escapes are not as it
interferes with ImageMagick’s SVG image handling. This was one of the
reasons the «» operator was created for IM version 6.


Protecting input text file from escape handling was finalised in
IM version 6.3.3.

notnever
IM reads text files, as literal text, without any escapes

Escaping Escapes


Before IM version 6.3.2, you could not use a backslash to escape an
initial » to turn off the ‘read from a file’ function. In
that case the only way to escape an initial » was to read
it from a file. This was not very practical in API’s.

Escapes on Older versions of IM


IM v6.2.4, percent escapes were removed from «» and «» as being non-sensible.

However they returned in IM v6.3.2, as a new ‘
construct, which can reference any image, made percent escapes in text to
image generators useful again. See .

If anyone like to create an automatic test for IM scripts, please
contribute. Or if you find such as test, please let me know.

Art-Like Transformations

Raise or Sunk Borders


In actual fact is achieved
by adding a Border, then raising it!

The operator only works on rectangular images, and will fail for images with
a transparent background, as the color modifications will also be transparent.
Basically is it a rather dumb operator!
{stroke width}  =  {border width} * 2 - 1

Random Pixel Spread

For example…

Also note that «»
also makes use of the .

Under Construction

For example, here I spread pixels with the original prepended as a referance.

rearrange vertical
pixel row

sigmaradius

Complex Polaroid Transformation


Polaroid is a registered trademark of the Polaroid Corporation.

For example, here I give a polaroid look to a photo thumbnail. The image is
looking up the spiral staircase (downward),
inside the Arc de Triumph, Paris. It is a very long staircase!.


Note the resulting image has a semi-transparent shadow, so you either have
to use a PNG format image, or «» the result onto a fixed background color for GIF or
JPG formats.

Index of Photos

The minus form of the operator lets you control the angle of rotation of the
image.

If the image has «» meta-data, that text will also be added into the lower
border of the polaroid frame, via the «» image creation operator. That is it will be word
wrapped to the width of the photo.

The other standard text settings (as per «»), allows you to control the look of the added caption.


The image meta-data attribute «» was used due to the internal use of «» text to image generator.

On the other hand the IM command «» uses «» as it uses the non-word wrapping «» text to image generator.

Image Distortion

RMagick Polaroid
EffectRubbleWeb IM Examples,
Other

Morphology
Methods

Charcoal, artists sketch of a scene


Technically the «» operator is a «» operator with some
thresholding applied to a grey-scale conversion of the original image.
 If anyone knows exactly what the emboss algorithm is supposed to do,
please let me know.


Do not use JPEG, GIF, or any other ‘lossy’ image encoding with Stegano

Encrypting Image Data


Do not use JPEG, GIF, or any other ‘lossy’ image encoding with Encryption

pass_phrase.txt


The encrypted image assumes it is saved using a 8 bit image file format. As
such it is recommended to enforce that limitation by setting «» before the final save
to the output file.

The «» was also needed in the above to ensure that the
output is not a palette or colormapped «png8:» image, which also does not
work properly.


Before IM v6.4.8-0 a binary file would stop at the first ‘NULL’ character it
finds. Something that would happen rather early if a PNG image was used.

The «» and
«»
operators was added to IM v6.3.8-6, but required you to include a
«» option in the build configuration.
However by IM v6.4.6 (when did it change?) this configuration item was no
longer needed and it became a standard configuration setting. As such you
can probably use it immedaitally.


The cipher was implemented using a self-synchronizing stream cipher
implemented from a block cipher.

This means that you can still decipher even a partial download of the image,
which was destroyed by transmission error, even though some part of the
image may have been destroyed. You also do not need to downloaded the whole
image to decrypt and examine the parts that was successfully downloaded.

But you do need the pass-phase to have any chance at all of successfully
decrypting the image, as it is a very very strong encryption.

Grids of Pixels

Here we generate a white on black ‘grid’ which is overlayed using (overlay white, while
leaving black areas as-is).

Here I generate circular ‘spots’ of color, but this time used a (overlay black, while
leaving white areas as-is).

For example, here I use to generate a diamond shaped ‘holes’ in a colored overlay. For
this a single ‘seed’ pixel is drawn and expanded using a .


Note that the «» coder will replace any transparency in
the image with the current background color. If you want to preserve the
transparency of the tiling image, either set «»
or «». The former is easier.

Computer Vision Transformations

Edge Detection

However by negating the image before doing the edge detecting, the twined lines
go inward and join together, removing the ‘twin line’ effect.

I have found that the edges tend to be too sharp, generating a non-smooth edge
to the resulting images. As such I find a very very slight blur to the result
improves the look quite a bit.

Announcment Examples

A negated edge generates an edge image but for the inside of the black area.

raster to vectorAutoTracer

vector form

Hough Line Detector

Wikipedia, Hough
Transform

backgroundline_colorWHthreshold

Now lets apply the Hough Line Detector to this image.

You can also see the intermedate ‘search image’, or ‘accumulator’ that is
looking for white pixels in every orientation, by using a special .

Local Adaptive Thresholding

Under Construction

For example.
   convert input.png -lat 17 output.png
Example
Example
The window does not need to be square.  for example...
  convert input.png -lat 15x25 output.png
  convert input.png -lat 15x25+2%
In summary, each pixel is thresholded using the following logic:
  AVG = average value of each pixel in the window
  IF (input pixel is > AVG + OFFSET)
     Output pixel is BLACK
  else
     Output pixel is WHITE

---

An alternative is to subtract a blurred copy of the original image
using (Modulus) Subtraction, then thresholding.

   convert rose: -colorspace gray -lat 10x10+0% x:

is roughly equivalent to...

   convert rose: -colorspace gray \( +clone -blur 10x65535 \) \
           -compose subtract -composite -threshold 50%  x:

The special "-blur 10x65535"  is a linear averaging blur limiting itself to a
10x10 window.

The 'Subtract' composition being a mathematical modulus type of operation will
wrap the values that goes negative back round to a value greater than 50%.

If you want to include an offset you can do so by also subtracting a solid
color background image by using a -flatten...  for example

   convert rose: -colorspace gray -lat 10x10+10% x:

is roughly equivalent to...

   convert rose: -colorspace gray \( +clone -blur 10x65535 \) \
           -compose subtract -background gray10 -flatten -threshold 50%  x:

   -adaptive-sharpen
        Sharpen images only around the edges of the images

   -segment cluster-threshold x smoothing-threshold
         Segmentation of the color space (not image objects)
         This can produce very verbose output.
         This applies the "fuzzy c-means algorithm" if you want to know more.

Also related is -despeckle. to remove single off color pixels.

Generate a 3d stereogram of two images (one for each eye)
This is also known as an anaglyph
  composite left.jpg right.jpg -stereo anaglyph.jpg

Append an Array of Images


The «» operator
will only append the actual images, and does not make use the virtual canvas
(image page) size, or the image offset. However the virtual canvas
information seems to be left in a funny state with the canvas sizes being
added together and the offset set to some undefined value.

This may be regarded as a bug, and means either the input images or result
should have the virtual canvas reset using «», before saving, or
using the image in operations where this information can become important.

This situation will probably be fixed in some future expansion of the
operation. Caution is thus advised, especially if re-appending images.

Frame Disposal Methods

afterbefore

Dispose Background — clear to background


There is some thinking that rather than clearing the overlaid area to the
transparent color, this disposal should clear it to the ‘background’ color
meta-data setting stored in the GIF animation. In fact the old
«» browser (version 2 and 3), did exactly that. But
then it also failed to implement the » dispose
method correctly.

On the other hand the initial canvas should also be set from the formats
‘background’ color too, and that is also not done. However all modern web
browsers clear just the area that was last overlaid to transparency, as
such this is now accepted practice, and what IM now follows.


Before IM version 6.2.6-1, the IM «» and «» operations
did not handle animations that used » disposal to
make pixels transparent, as per all the major web browsers. See Animation Bugs for examples and
details.

These functions however did work fine when no pixel clearing was applied
or intended. This has now been fixed for «» and the «‘ method was created
to replace the use of «» as a GIF animation frame optimizing function.

Hole Filling

Creating a hole to fill

Suppose we have an image with some ugly text…

Well what we really want to do is remove that text, and the simplest way is
to mask it, so as to leave a ‘hole’ where the text was. This simplifies the
problem, as it no longer matters what was removed. We just have a hole to be
filled.

For this case however I’ll create a mask using a drawn line that covers the
‘ugly text’, as if an user had quickly used an image editor.

Now lets use the mask to cut a hole out of the image, which will also check
that it covers all the unwanted parts.

So here we have an image with a ‘hole’ in it that needs to be filled.

Blurred Fill

One of the simplest methods is to simply blur the image, allowing the colors
around the hole to ‘spread’ into the hole, and then remove the transparency.

The amount of blur you use depends on the size of the hole used.

Under Construction

snibgo, Filling holessnibgo, Filling holes in priority orderColor
Diffusion
Diffusion CurvesText Removal DiscussionFill area with
nearest colour from boundaryStack Overflow, Remove text from jpegPython
OpenCV inpainting

Created: 10 December 2003 (originally ‘channels’)
Updated: 2 October 2018
Author: Anthony Thyssen, <Anthony.Thyssen@gmail.com>
Examples Generated with:

URL:

Background Removal

Removing a Known Background

Alpha Composition

By separating and adding the individual color channels together and
thresholding we get a mask of any difference in any channel between the two
images.

Using this mask we can set anything that has not changed to transparency.

hole

Recovering Semi-Transparent Edges

-fuzz 1%

-fuzz 3%

-fuzz 6%

-fuzz 28%

-fuzz 32%

-fuzz 34%


You will need to somehow figure out what color the semi-transparent pixels
should be, so you can set the correct color for the anti-aliasing pixels.

This could be

A fixed edge color (EG: near-black, as in this example)

Use the color of nearest fully-opaque edge pixels (using
morphology. See

Calculated: Once you know th alpha and the background color,
you can subtract the background color to correct the pixel color.
See below.

Basically it depends on your image.

Background Removal using Two Backgrounds

Chroma Key Masking

HugoRuneUndo a Composite -dissolve


In IM v6.6.8-3, if FX references a transparent pixel using ‘p{}’ it gets
zero values rather than the actual fully-transparent color values!
This is a bug and was reported and fixed in IM v6.6.8-5. It is not known
when the bug was introduced.

This was only a problem, if you decide to merge the alpha image into the
source image first, then try to fix semi-transparent or ‘spill’ colors,
using the known background color.

Studio photos for background recoveryIf you try this please let us know, and give an example of your source
photos and results for inclusion here. You will be named with a pointer to
your site for people to look at.
Video background recoveryIM Forum Discussion

Text — Pages of Plain Text


Do not confuse the «» file input format with the
similar «» input format.
The latter will first attempt to read the file as a » image format.

That doesn’t mean that a plain text file with a «» will
fail. In fact such a file will probably be converted as you would expect,
as the «» file format will
automatically fall back to the «» format if an enumerated
image is not recognised.


The input text data read from the file is essentially passed directly to the
font library to draw the UTF text. As a consequence of this some control
characters may be drawn using unusual ‘glyphs’. This includes
and characters, which, at the time of
writing, the ‘freetype‘ library gets wrong.

If this is a concern, you may like to pre-process your text file using a
filter program, such as «», to convert
characters into the appropriate number of spaces.


The above manual to image conversion however generates multiple pages
(images), so I the second and
later ones to leave me with just the first page, instead of a GIF
animation of all the pages.

I could also have appended a , » input filename, such as
«», to tell IM only to read the first image
generated. Though at this time all the page selection is still handled by
generating all pages and deleting the unwanted pages.

Trimming Text Pages


Almost all other image creation operators use the «» setting to set a larger
virtual ‘canvas’ and an ‘offset’ for the image on that canvas, generally for
the purpose of layering images or generating animations. Because of this it
is probably a good idea to reset your page setting using «» after any
«» or «» operation, or you may get
unexpected results for any secondary images you may latter read in on the
same command line.

This also is why I added a «» operator to the above example otherwise the text is
offset, and the image generated is also offset!

For more details of using this offset see .

multiple pagesmultiple imagesafter

Drawing Special Characters in the Text String

To Quote or Backslash?

and


  -draw "... text 0,0 'string' ..."
  • Using Single Quotes for the shell argument,
    with Double Quotes around the MVG text string.

    The simplest technique for handling draw text strings is to use a single
    quote for the wrapping shell argument. This however means that to include
    an apostrophe in the drawn string you need to leave the shells ‘single
    quote mode’ and supply that apostrophe outside the shells single quotes.

    For example here is how to handle the four special characters I talked
    about.

    Note that as the dollar sign is not needing escaping, you also can not use
    it to substitute the contents of a shell variable.

    It is important to remember that the backslash is the only special
    character that the IM draw string handles. Also its reason for existence
    is purely to allow you to escape any ‘IM draw string quotes’, such as we
    used above for the double quotes. Beyond this, all the other weirdness is
    caused by the UNIX command line shell, and not IM.

    PC-DOS has its own weirdness, and I would appreciate input on escaping
    special characters when using IM from environment.

  • Using Double Quotes for the shell argument,
    with Single Quotes around the MVG text string.

    If you do want want to insert a ‘shell variable’ into the drawn string,
    then you will have to use double quotes for the outside shell argument.
    This makes the whole matter much more complex, as you lose the protection
    of the shell and you now have to not only escape the dollar
    » signs, but also backslashes » as well.

    On the other hand, the shell will not then need to use single quote
    characters as its end-of-argument de-limiting character, so that aspect is
    simplified.

    Lets summarize the results for our short list of special characters.

    Notice that if you want to draw a backslash itself, the MVG text string
    needs the backslash to be doubled (as in the previous example), but the
    shell itself also needs each of those backslashes doubled, producing a
    total of four backslashes just to produce one such character.

    This doubling can very quickly become overwhelming and confusing,
    requiring lots of backslashes to achieve what you want. Just take is slow
    and easy, and you will figure it out for your situation.

  • Using Single Quotes for the shell argument,
    with Single Quotes around the MVG text string.

    Lets finish this off with a summary of the final two quoting combinations.
    I’ll leave you to figure out how they are decoded by the shell and MVG.

  • Using Double Quotes for the shell argument,
    with Double Quotes around the MVG text string.

About Percent Characters

Just one final point about special ‘escape’ characters in the «» operator. Percent
characters » should draw ‘as is’. You should not need to do
anything special to draw them. If they don’t draw ‘as is’, then you have an
old version of IM and should upgrade ASAP.


Up until IM version 6.2.4, the » character was used as an
escape character to include extra image information in the drawn text
string. This is no longer the case as such escapes were confusing and
incorrect when SVG images also tried to draw percent characters.

Drawing a Percent
Bug
Annotate instead of Draw

The better way of avoiding these types of problems is to use «» rather than draw for
text drawing. This operator is a wrapper around the draw operator and allows
the use of all the capabilities of draw, but in a simpler form.

Basically this operator only need one set of quoting (for the shell). This
makes dealing with special characters a much much simpler.

Unfortunately while you no longer need to escape quotes for IM, you now have

Adding/Removing Image Edges

Border, adding space around the image


As shown above the default color used by the «» operator is a light
gray as it matches nicely the default grey page color of web pages on the
WWW.

The fact that adding a border to images with transparency, also by default
fills the transparent background of the image, has been the cause of some
debate amongst IM users and the development team. A summary of this debate
is given on .

Alpha Compositing Examples

Border and Virtual Canvas

Frame, adding a 3D-like border


The default «» is a slightly darker gray than that of the default
setting of «». This also allows it to match the default gray
color of web pages on the WWW (used by early browsers such as
«» and «». (See below)

While «» may
actually use the «» color, it also generates four more extra colors
from this base for use in drawing the frame. That is five related colors
will likely be added to an image, not just one.

Frame and Alpha Composition


The fact that adding a frame to images with transparency, also by default
fills the transparent background of the image with the bordercolor has
caused some debate amongst IM users and the Development team. A summary
of this debate is given on .


The use of «-bordercolor» as the background image for both «» and «» was added to IM with
version 6.1.4. Before this the background canvas generated consisted of a
black canvas onto which the border, or frame was drawn.

This use of black was especially bad for the «»
command which makes heavy usage of the internal «» function in its internal
processing. (See )

Frame and Virtual Canvas

Shave, removing edges from an image

opposite


Before IM version v6.6.1-0, equal-sized tile cropping for images
with a canvas offset (such as the above) was broken.

Extent, Direct Image Size Adjustment


Before IM version v6.3.2, «» just cleared the memory of any new areas to zero, or
straight black. It did not fill the areas with «» color.

You can even use offsets, which basically means the is simply a straight forward with
background padded fill, regardless of position.

Special Image Masks

Write Masks — Protecting Pixels from Change

The «» operator defines a ‘write-protect’ mask

A three image «» operation uses
a ‘write’ mask

Cleaning up noise around
textNOTE: -crop should be able to preserve the image mask of individual
images, by also cropping the mask and assigning to the new images. This
however is currently not done.

Clip Mask and Clip Paths


In IMv6, a ‘write-mask’ and ‘clip-mask’ are implemented side-by-side, even
though they technically do exactly the same function. As such you could
apply both masks simultaneously.

However using both at the same time is not recommended, and results are not
defined. Also this ‘boolean mask’ form has been removed from IMv7.

BlursMorphologyConvolution


The result is using a Write-Protect Mask and is not what was wanted.

Mathematics on Gradient Images

word of warningbiased gradients

Attenuate a Biased Gradient

Amplitude Modulation

Of course you can do the whole process all in the one command, and it does not
have to be a simple linear attenuation either. For example here I attenuate
the high frequency Sine wave, using a negated Cosine wave, instead of a linear
gradient.

attenuate

Sign of Gradient
white = negative
Bias Offset
Absolute Value
sign

Frequency Modulation

Frequency Modulation

Under Construction

Miscellaneous Image Transformation Techniques.

These have not been exampled yet, but are some basic IM developed transforms
that may provide useful.  If you have an interesting effect please contribute.

   pixelize an image
      resize an image down 10 then scale the image 10 to produce blocks
      of roughly averaged color.
      For example...
         convert input.jpg -resize 10% -sample 1000% output.jpg

  De-skew slightly rotated images

    -deskew {threshold}
       straighten an image. A threshold of 40% works for most images.

    Use -set option:deskew:auto-crop {width} to auto crop the image. The set
    argument is the pixel width of the image background (e.g 40).

    Programmically we auto crop by running a median filter across the image
    to eliminate salt-n-pepper noise.  Next we get the image bounds of the
    median filter image with a fuzz factor (e.g. -fuzz 5%).  Finally we
    crop the original image by the bounds.  The code looks like this:

      median_image=MedianFilterImage(image,0.0,exception);
      geometry=GetImageBoundingBox(median_image,exception);
      median_image-DestoryImage(median_image);

      print("  Auto-crop geometry: %lux%lu%+ld%+ld",
                geometry.width,geometry.height, geometry.x,geometry.y);
      crop_image=CropImage(rotate_image,&geometry,exception);

    See 

  Segmentation
    look at scripts
       divide_vert
       segment_image
    for some simple scripts I wrote to segment well defined images into
    smaller parts.   I hope to get simple segmentation functions like this
    into the core library, to allow for things like automatic sub-division of
    GIF animations, and seperating images and diagrams from scanned documents.


Created: 15 March 2004
Updated: 18 June 2009
Author: Anthony Thyssen, <Anthony.Thyssen@gmail.com>
Examples Generated with:

URL:

Indexes of Image Directories

HTML Thumbnail Image Maps

Photo
Images


IM ExamplesPhoto Store

Note the use of » instead of just
». This is important as the image is being resized as it
is read in. The former will label the images with their original pixel size
as it is on disk, while the latter will use the current resized size of the
image. This is something that is easily overlooked by users.

Image Property EscapeThumbnail Examples Page

Smaller HTML Index Maps, using JPEG images


IM ExamplesPhoto Store
  • First I generate a montage thumbnail HTML index, as I did previously.
    This generated the files: «» and
    «»
  • I then converted the PNG image to a smaller, lossy, JPEG image.
  • Then I used a small » one line script to
    change HTML file to use the JPEG image instead of PNG.
  • And finally I removed the PNG image, as well as the SHTML map file which
    I don’t need.

Visual Index ofPhoto Store

Visual HTML ofPhoto Store

Fonts

Under Construction


As for ordering the font paths, that is simply ordering the fonts specified in
the XML files.

The start point is the system fonts, followed by the system installed
"type.xml" file, on my system this is "/etc/ImageMagick-6/type.xml".

This system installed "type.xml" file is typically just a list of 'include'
other type-* files.  And the order of the includes will specify the order of
Extra System Fonts, verses Ghostscript Fonts.

After that file other "type.xml" files are looked for, such as in 'home'
directories, or even current directory.

Later fonts will NOT replace earlier fonts, as such if two fonts have that
same name, only the first one will be noted by IM. (a security measure).

To see the fonts loaded use
    convert -list font

It lists "Path:" of the type file each font list was found in, but the
paths are listed in REVERSE order, with system fonts at the end.

I have for example a personal Font named "Courier", but it is not listed in
the above list as it was defined after the "Courier" that was found in the
"System Fonts" area, (which is listed at the end of the above output).

On the other hand my own personal font "CourierNew", is listed, as it does not
clash with any system or system config defined font.

To see what font glyph file is selected for soem specific request
use...
  convert -debug annotate xc: -font Courier \
          -annotate 0 'Test' null: 2>&1 |
    grep '^ *Font '

Montage, Introduction

Tile Layout Controls


The strange «» syntax is an UNIX shell shorthand, which
is expanded into a list of filenames. The «» command
itself does not see these characters, just the resulting list of files.
Num Images Tile Setting
1
1×1
2
2×1
3
3×1
4
2×2
5 — 6
3×2
7 — 8
4×2
   
Num Images Tile Setting
9
3×3
10 — 12
4×3
13 — 15
5×3
16 — 20
5×4
21 — 24
6×4
25
5×5
   
Num Images Tile Setting
26 — 30
6×5
31 — 36
7×5
31 — 35
7×5
36
6×6
37 — 42
7×6
43 — 48
8×6


Before IM v6.1 montage would automatically truncate the extra space if the
number of images did not use that space. As such a setting such as the
first «» image would have been truncated to produce a
«» tile image.

Because of this, past users of montage often used large numbers such as
«» to generate a single row of images. Now such a
argument will produce a very long image, and could take a long time for IM
to complete. As such…


Avoid the use of very large tile numbers in IM montage!

Border Decoration


The «»
decoration does not currently work when the is also applied.


Before IM v6.1.0 (approx) -border would been applied to images at the point in
which it appeared in the «» command line, just like
it would have with «».

That is border would have been thus added to the image long before the
images get resized (according to «»), which resulted in different border widths
around each image depending on the size of the image at that point. It
was to remove this inconsistancy that -border became a special montage setting.

Labeling Montage Images

not

Image Property
Escapes


Note that ‘ gives the current pixel width and height of
the image as it is in memory. If the image size was modified, such as
during input this may be different to the images in disk (or creation) size.
Use » instead if you want its in memory
pixel size.


Either label all your images, or none of them!

GIMP

Leaving Gaps in a Montage


There is no method, at this time to allow montaged images to span multiple
rows or columns, as you can in HTML tables. Nor can you generate variable
sized rows and columns to best fit the array of images being generated.

If you really need this sort of ability you will need to develop your own
montage type of application. If you do develop something, then please
contribute, and we’ll see about merging it into the existing montage
application.

Some solutions for this includes labeling and framing the image thumbnails
yourself and then using either or use a more free form technique.

Determining Font Metrics, without using an API


The «» method was added to IM v6.3.9-2

Older techniques

Here is the image we will be studying, as a reference. You don’t actually
need to drawn and save it as an image, as we are only extracting data, not an
image. the colors of this image will be modified so we can look at the white
and black parts separately using «» to extract the metrics used.

Note that not all fonts limit their drawing
to within their defined drawing bounding box! However some letters can
extend far outside those boundaries. That is why the above example sets
a «» color of
». That way ill behaved fonts will not effect the above
measurements.

before


The dimensions extracted from a font will also vary with the current
«»
used for drawing the font. If you increase the size of the outline
stroke, then the dimensions (and bounding box size) needed to draw the
font is also expanded by the same amount to accommodate the thicker outline.

Dimensions also vary with the operating system, (type and version) and the
version of the delegate font drawing library IM is using on that system,
even when the exact same font library and IM version has not changed.
Caution is recommended when different computers could be used for text
drawing, as results can vary even for the same font.

TrueType
Fundamentals (PDF)

Drawing Symbols

Symbol Drawing Techniques


The relative move item » is
broken before IM v6.4.3-5. If your IM is older than this, the above (and
next) examples may not draw anything. You can fix this for older versions
by replacing the relative moves » in the above with an
appropriate sequence of relative lines, ».

Alternatives to Drawing Symbols

Convolution


Before IM v6.7.6-9 The requires the transparency channel of the image to be given as
‘matte’ values rather than alpha values, as such the resulting alpha channel
created needs to be negated. EG:

A Fun Experience with IM

Layered

Layers of Images

Drawing Circles

Fred Weinhaus


The relative move item » is
broken before IM v6.4.3-5. If your IM is older than this, the circle may
only appear as a single pixel. You can fix this for older versions by
replacing the » in the above with a ».

Fred Weinhaus

Drawing Arrows
— position, rotate and scale symbols

  • Measurement where you simply want to mark the ends of a line
    with an arrow head to indicate the limits of a measurement in some
    engineering diagram. Very simple.

  • Vectors, showing direction and intensity of some value.
    For example in a weather wind chart. A tail is required and the 0,0 point
    is the end of the tail. Often a large grid of such vectors is created.

  • Indicators, that point out some detail.
    For this the 0,0 point probably should be either the tip, or some distance
    in front of the arrow itself.
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