# Images.rb
module Tioga
# These are the methods for creating and using images in PDF graphics.
# See also Tutorial::SampledData.
class Images < Doc < FigureMaker
=begin rdoc
Shows the image specified by the dictionary argument _dict_. The image can be taken from a JPEG file
or it can be given as sampled data to be mapped to colors for pixels.
Some of the dictionary entries give the properties of the image itself and some deal with
the placement of the image in the figure. Conceptually the image is a rectangle with the
first row of data at the top and the last row at the bottom. The first column in each row
is at the left and the last column is at the right. This image rectangle is mapped to the
figure by giving the figure coordinate locations for the lower left, lower right, and upper
right corners of the image. This allows the image to be rotated, streched, and skewed when
it is placed -- or even reflected in either the horizontal or vertical by suitable choices
for the corner locations.
For a JPEG, you can simply give the filename for the image along with the location and the
width and height. Sampled images can be monochrome, gray scale, RGB, or CMYK according to the value of the
'color_space' entry.
The 'color_space' entry is set to 'MONO' or 'mono' for a monochrome image. The monochrome image is used as
a 'stencil mask' for painting in the current fill color. The default is to paint places corresponding
to sample values of 0 while leaving the previous contents unchanged where the sample value is 1.
If the entry 'reversed' is +true+, then this interpretation is reversed, and 1's are painted and 0's left unchanged.
The data for monochrome images is stored using a single bit per sample. The routine create_monochrome_image_data
provides an easy way to create such data from a table of arbitrary sample values.
Monochrome images can also be used as a stencil mask for other images. You can supply a dictionary
with entries for a monochrome image as the value of the 'stencil_mask' entry for another call on show_image,
and the second image will then only be painted in the places where the stencil mask image would itself
be painted. Note that in this case, the second image and the stencil mask image need not have the
same number or rows or columns: each image rectangle is mapped to the figure using the same locations
for 'll', 'lr', and 'ul' so their boundaries will coincide even if they are different resolutions.
The 'color_space' entry is set to 'GRAY', 'gray', 'GREY', or 'grey' for a grayscale image. The data for
grayscale images is stored using one byte per sample. The routine create_monochrome_image_data provides
a handy way to create such data from a table of values.
Grayscale images can also be used as a "soft mask" for other images. In this case, the grayscale samples
are interpreted as relative opacities (a stencil mask, on the other hand, is "hard" in that each
sample is either totally opaque or totally transparent). To use such soft masking, create a dictionary for the grayscale
image and provide it as the 'opacity_mask' entry for the image be be masked.
The 'color_space' entry is 'RGB' or 'rgb' for an image using the red-green-blue representation. Samples
are stored as three bytes, corresponding to red, green, and blue intensities
(e.g., red intensity in range 0.0 to 1.0 is stored as round(red*255)).
If the 'color_space' entry is 'HLS' or 'hls', then samples
are stored as three bytes, corresponding to hue, lightness, and saturation
(the hue angle in the range 0.0 to 360.0 is stored as round(hue*256/360)).
[Note: internally, the hls data is copied and converted to rgb -- see string_hls_to_rgb.]
In 4-color printing, as in ink-jet printers, images are painted using cyan, magenta, yellow, and black inks.
The corresponding 'color_space' is 'CMYK' or 'cmyk'. For this case, samples are stored as four bytes,
corresponding to cyan, magenta, yellow, and black intensitites.
Finally, many applications use "false colored" images to represent data values. The data is stored one byte
per sample, and a color map is used to determine the RGB intensities representing different sample values.
The routine create_image_data is available to help construct such a representation from a Dtable of
double precision samples. In some situations, the data may contain "out-of-range" or "invalid" entries
that should not be displayed. This can be accomplished by using a certain byte value to represent
such cases and providing a 'value_mask' entry with the image (this is also called "color key masking").
The value mask entry is a pair, [min_mask_byte max_mask_byte], and any samples whose value falls into
this range are not painted, allowing the existing background to show through. (For the common case in
which a single byte code is being used for all "out-of-range" data, 'value_mask' can simply be set to
this byte code.) The use of a 'value_mask' is in effect a
stencil mask that is determined on-the-fly by the sample values themselves. The routine create_image_data
has options for doing value masking.
Image Interpolation: When the resolution of a source image is significantly lower than that of the output
device,
each source sample covers many device pixels. This can cause images
to appear "jaggy". These visual artifacts can
be reduced by applying an
image interpolation algorithm during rendering. Instead of painting all pixels covered
by a source sample with the same color, image interpolation attempts to produce
a smooth transition between
adjacent sample values. Image interpolation is enabled by
default in Tioga; setting the 'interpolate' entry
in the image dictionary to +false+ should disable it
(but note that some PDF viewer implementations seem to ignore this flag).
Dictionary Entries
'll' => [x, y] # location for the lower-left corner of the image
'lr' => [x, y] # location for the lower-right corner of the image
'ul' => [x, y] # location for the upper-left corner of the image
'width' => an_integer # number of columns of samples in the image
'w' # alias for 'width'
'height' => an_integer # number of rows of samples in the image
'h' # alias for 'height'
'jpg' => a_string # file containing the JPEG image
'jpeg', 'JPEG', 'JPG' # aliases for 'jpg'
'color_space' => string_or_colormap # tells how to interpret the image data
'colormap' # alias for 'color_space'
'color_map' # alias for 'color_space'
'data' => a_string # samples with 'width' columns and 'height' rows
'value_mask' => [min_mask_byte max_mask_byte] # for color key masking of image
'value_mask' => byte_code_integer # sets both min_b
'stencil_mask' => a_mono_image_dict # for stencil masking of image
'opacity_mask' => a_grayscale_image_dict # for soft masking of image
'reversed' => true_or_false # default false. for mono images only.
'interpolate' => true_or_false # default true
Examples
On the left
show_image( # Cassini image of Jupiter with Io in foreground
'jpg' => "data/cassini.jpg", 'width' => 999, 'height' => 959,
'll' => [0.01, 0.01], 'lr' => [0.99, 0.01], 'ul' => [0.01, 0.99])
In the center
show_image( # same image of Jupiter
'jpg' => "data/cassini.jpg", 'width' => 999, 'height' => 959,
'll' => [0.01, 0.01], 'lr' => [0.99, 0.01], 'ul' => [0.01, 0.99])
fill_opacity = 0.6 # images can be partially transparent too
show_image( # Lucy amazed by Io
'jpg' => "data/lucy.jpg", 'width' => 148, 'height' => 164,
'll' => [0.52, 0.97], 'lr' => [0.41, 0.52], 'ul' => [0.12, 0.97])
On the right
1) show_image of lucy
2) create_monochrome_image_data for checker board pattern
3) show_image of Jupiter using the monochrome image data as a stencil_mask
link:images/Sample_Jpegs.png
The following is a more lengthy example showing the use of a "false colored" image to
represent a 2 dimensional table of data. In this case, the data comes from
an astrophysical "equation of state" code that gives pressure as a function
of temperature and density. The data is read from a file (using Dtable.read),
converted to image samples (by create_image_data), and displayed (by show_image)
using one of the predefined colormaps (mellow_colormap). Since there is no data
for the high-temperature and low-density corner, that area is removed by a clip path
(see the clip_press_image method below). Finally, a color bar is added showing
the values for the different colors used in the image. The top-level plot method
is 'sampled_data' which shows the image in one subplot and the colorbar in another.
def sampled_data
t.rescale(0.8)
t.subplot('right_margin' => 0.07) { eos_image }
t.subplot(
'left_margin' => 0.95,
'top_margin' => 0.05,
'bottom_margin' => 0.05) { color_bar }
end
def eos_image
t.do_box_labels('Pressure', 'Log Density', 'Log Temperature')
data = get_press_image
xs = @eos_logRHOs
ys = @eos_logTs
t.show_plot('boundaries' => [@eos_xmin, @eos_xmax, @eos_ymax, @eos_ymin]) do
t.fill_color = Wheat
t.fill_frame
clip_press_image
t.show_image(
'll' => [xs.min, ys.min],
'lr' => [xs.max, ys.min],
'ul' => [xs.min, ys.max],
'color_space' => t.mellow_colormap,
'data' => data, 'value_mask' => 255,
'w' => @eos_data_xlen, 'h' => @eos_data_ylen)
end
end
def get_press_image
@eos_xmin = -8.5; @eos_xmax = 2.5
@eos_ymin = 5.7; @eos_ymax = 7.0
@image_zmin = 8
@image_zmax = 18
data = Dvector.read("data/density.data")
@eos_logRHOs = data[0]
@eos_data_xlen = @eos_logRHOs.size
data = Dvector.read("data/temperature.data")
@eos_logTs = data[0]
@eos_data_ylen = @eos_logTs.size
@pres_data = Dtable.new(@eos_data_xlen, @eos_data_ylen)
@pres_data.read("data/pressure.data")
@pres_data.safe_log10!
return t.create_image_data(@pres_data.rotate_ccw90,
'min_value' => @image_zmin,
'max_value' => @image_zmax,
'masking' => true)
end
def clip_press_image
t.move_to_point(t.bounds_left, t.bounds_bottom)
t.append_point_to_path(t.bounds_left, 6.355)
t.append_point_to_path(-6.05, t.bounds_top)
t.append_point_to_path(t.bounds_right, t.bounds_top)
t.append_point_to_path(t.bounds_right, t.bounds_bottom)
t.close_path
t.clip
end
def color_bar
xmin = 0; xmax = 1; xmid = 0.5
t.rescale(0.8)
t.xaxis_type = AXIS_LINE_ONLY
t.xaxis_loc = BOTTOM
t.top_edge_type = AXIS_LINE_ONLY
t.yaxis_loc = t.ylabel_side = RIGHT
t.yaxis_type = AXIS_WITH_TICKS_AND_NUMERIC_LABELS
t.left_edge_type = AXIS_WITH_TICKS_ONLY
t.ylabel_shift += 0.5
t.yaxis_major_tick_length *= 0.6
t.yaxis_minor_tick_length *= 0.5
t.do_box_labels(nil, nil, 'Log Pressure')
t.show_plot('boundaries' => [xmin, xmax, @image_zmax, @image_zmin]) do
t.axial_shading(
'start_point' => [xmid, @image_zmin],
'end_point' => [xmid, @image_zmax],
'colormap' => t.mellow_colormap
)
end
end
link:images/Sampled_Data.png
=end
def show_image(dict)
end
=begin rdoc
Creates a data representation suitable for use with show_image from the values in the Dtable _data_
according to the entries in the dictionary _dict_. Only _data_ rows between 'first_row' and
'last_row' and columns between 'first_column' and 'last_column' are included.
Data values between 'min_value' and 'max_value'
are mapped linearly to numbers between 0 and 'max_code' and then rounded to the nearest integer.
Data values less than 'min_value' are mapped to the integer specied by 'if_below_range', and
values greater than 'max_value' are mapped to the integer given by 'if_above_range'.
If the flag 'masking' is +true+, then 'max_code' is set to
254 and all data values out of range are assigned the code 255. The result can then be used in a call to
show_image with 'value_mask' set to 255 to prevent out-of-range values from being displayed.
Dictionary Entries
'first_row' => an_integer # first row of data to include (default 0)
'last_row' => an_integer # last row of data to include (default -1)
'first_column' => an_integer # first column of data to include (default 0)
'last_column' => an_integer # last column of data to include (default -1)
'min_value' => a_float # lower bound on valid data
'max_value' => a_float # upper bound on valid data
'masking' => true_or_false # default false
'max_code' => an_integer # integer between 1 and 255 (default 255)
'if_below_range' => an_integer # integer between 0 and 255 (default 0)
'if_above_range' => an_integer # integer between 0 and 255 (default max_code)
Example: For an image that only shows the data values between 0 and 1 and masks out other
values, you might do this:
create_image_data(data, 'min_value' => 0, 'max_value' => 1, 'masking' => true)
=end
def create_image_data(data, dict)
end
=begin rdoc
Creates a data representation suitable for use with show_image from the values in the Dtable _data_
according to the entries in the dictionary _dict_. Only _data_ rows between 'first_row' and
'last_row' and columns between 'first_column' and 'last_column' are included.
If the 'reverse' flag is +false+, values greater than 'boundary' map to 1's and other values map to 0's.
If 'reverse' is +true+, then values greater than 'boundary' map to 0's and other values map to 1's.
Dictionary Entries
'first_row' => an_integer # first row of data to include (default 0)
'last_row' => an_integer # last row of data to include (default -1)
'first_column' => an_integer # first column of data to include (default 0)
'last_column' => an_integer # last column of data to include (default -1)
'boundary' => a_float # default 0.0
'reverse' => true_or_false # default false
=end
def create_monochrome_image_data(data, dict)
end
end # class
end # module Tioga