User:River/Crop ratios on paper
Contents
This wiki post outlines a Python script which produces ConTeXt output. The code output crops pages to size at a given ratio and scale. The code might benefit from some tweaks, alternative default behaviour and additional features. Nevertheless, interpolation is put to use in a command line interface and I found it interesting to share for this reason. I plan to produce more ideas for similar algorithms in the near future.
import argparse import math import pandas as pd import numpy as np from sklearn.preprocessing import MinMaxScaler
To set up a command line application the argparse module is used. Argparse allows for flags and positional arguments to be given to the script when executed at the command line. The values passed in by the user are stored in variables. Argparse also implements a help flag which offers information about available flags.
parser = argparse.ArgumentParser(description='Crop typesetting areas.')
Arguments are added. outfile is a positonal argument whereas the remaining arguments are flags. The flags will be looked at in more detail later on.
parser.add_argument('outfile',
metavar='OUTFILE',
nargs=1,
help="Write to a file")
parser.add_argument('--papersize',
metavar='PAPERSIZE',
nargs=1,
default='A4',
help="Provide a standard papersize")
parser.add_argument('--ratio',
metavar='RATIO',
nargs=1,
default='2:3',
help="Crop the paper to this proportion")
parser.add_argument('--orientation',
metavar='ORIENTATION',
nargs=1,
default='portrait',
help="Switch between portrait and landscape.")
parser.add_argument('--scale',
metavar='SCALE',
nargs=1,
default=[90.0],
help="Scale the size of the cropped page.")
_StoreAction(option_strings=['--scale'], dest='scale', nargs=1, const=None, default=[90.0], type=None, choices=None, required=False, help='Scale the size of the cropped page.', metavar='SCALE')
For the sake of example, let’s pass the following arguments to the script.
args = parser.parse_args(args=['--scale', '90',
'--ratio', '5:3',
'--papersize', 'A3',
'--orientation', 'landscape',
'main.tex'])
Wishlist
It would be interesting to add a --page-on-page flag which introduces variation in the output. When active, this flag would print the cropped page on the given page size at the given scale and ratio. This is the default behaviour at the moment. Implementing this flag would result in an alternative default behavior where the output is a page already cropped to size.
Papersize Dictionary
I drew up a dictionary of A-series papersizes based on information at papersizes.io. This way paper dimensions can be referenced by name.
portrait_paper_sizes = {
# size width height (mm)
"A0" : [841, 1189],
"A1" : [594, 841],
"A2" : [420, 594],
"A3" : [297, 420],
"A4" : [210, 297],
"A5" : [148, 210],
"A6" : [105, 148],
"A7" : [74, 105],
"A8" : [52, 74],
"A9" : [37, 52],
"A10": [26, 37],
"A11": [18, 26],
"A12": [13, 18],
"A13": [9, 13],
"2A0": [1189, 1682],
"4A0": [1682, 2378],
"A0+": [914, 1292],
"A1+": [609, 914],
"A3+": [329, 483]
}
Portrait and Landscape
I figured I would implement portrait and landscape orientations into the script. Portrait mode is enabled by default. Passing --orientation landscape to the command switches to landscape output. It might be more concise to have a --landscape flag.
if "portrait" in args.orientation:
paper_width = portrait_paper_sizes[args.papersize[0]][0]
paper_height = portrait_paper_sizes[args.papersize[0]][1]
print(args.papersize[0], "portrait", paper_width, "mm x", paper_height, "mm")
I have not accounted for a situation in which someone provides a papersize which is not listed in the dictionary. I expect that at the moment, the script will throw an error if this happens. In any case, it’s necessary to exchange the values of the width and height in landscape mode. This can be done in an least two ways. I decided to change the indexes like so.
if "landscape" in args.orientation:
paper_width = portrait_paper_sizes[args.papersize[0]][1]
paper_height = portrait_paper_sizes[args.papersize[0]][0]
print(args.papersize[0], "landscape", paper_width, "mm x", paper_height, "mm")
A3 landscape 420 mm x 297 mm
Bu it is also possible to switch the values of paper_width and paper_height by creating a new dictionary of landscape paper sizes. The code commented out below does that.
# if "landscape" in args.orientation:
# landscape_paper_sizes = {}
# for size in portrait_paper_sizes:
# landscape_paper_sizes[size] = portrait_paper_sizes[size][::-1]
# paper_width = landscape_paper_sizes[args.papersize[0]][0]
# paper_height = landscape_paper_sizes[args.papersize[0]][1]
# print(args.papersize[0], "landscape", paper_width, "mm x", paper_height, "mm")
Ratio
ratio = args.ratio[0].split(":")
ratio_x = int(ratio[0])
ratio_y = int(ratio[1])
print(f"Crop ratio: {ratio_x}:{ratio_y}")
Crop ratio: 5:3
The ratio is provided to the script with the --ratio flag. By default the ratio is 2:3. Some calculations need to be done so let’s initialise some variables.
possible_widths_list = [] possible_heights_list = [] w = ratio_x h = ratio_y
In order to ascertain the size of the cropped page, I’m calculating a list of measurements. These measurements indicate towards the 2D area of the cropped page. The values are later used in the context of the scale feature. The following calculation checks the ratio against the dimensions of the page. A for loop is used to provide a limit to the length of the list which contains the measurements described above.
if (math.floor(paper_width / ratio_y)) > (math.floor(paper_height / ratio_x)):
# If the paper is landscape
for dimension in range(math.floor(paper_width / ratio_x)):
possible_widths_list += [w]
possible_heights_list += [h]
w += ratio_x
h += ratio_y
else:
for dimension in range(math.floor(paper_height / ratio_y)):
possible_widths_list += [w]
possible_heights_list += [h]
w += ratio_x
h += ratio_y
Pandas, Numpy and Sklearn
At the beginning of the script, I imported (parts of) these modules into the python script. This was to enable python to make use of different mathematical functions. In particular, I’m going to use a pandas DataFrame, SciKit Learn’s MinMaxScaler and Numpy’s interp function. The purpose is to provide the user with the ability to scale the size of the cropped page in the output. In short, the values in possible_widths_list and possible_heights_list are adjusted to a percentage scale. That there can be more or less than 100 values in the possible_widths_list and possible_heights_list means that the value of the length of the list needs to represents 100%. To begin with, let’s create a DataFrame and a scaler. Some of the code which appears below was adapted from this website.
df = pd.DataFrame({"widths": possible_widths_list, "heights": possible_heights_list})
scaler = MinMaxScaler()
Visualising the dataframe
The dataframe resembles a table of widths and heights spanning a range of values.
print(df)
widths heights 0 5 3 1 10 6 2 15 9 3 20 12 4 25 15 .. ... ... 79 400 240 80 405 243 81 410 246 82 415 249 83 420 252 [84 rows x 2 columns]
Adding scaled values to the dataframe
This code assigns a percentage-based value to each possible width and height.
tmp_widths = df.widths - df.widths.min() tmp_heights = df.heights - df.heights.min() scaled_widths = tmp_widths / tmp_widths.max() * 100 scaled_heights = tmp_heights / tmp_heights.max() * 100 df["scaled_widths"] = scaled_widths df["scaled_heights"] = scaled_heights print(df)
widths heights scaled_widths scaled_heights 0 5 3 0.000000 0.000000 1 10 6 1.204819 1.204819 2 15 9 2.409639 2.409639 3 20 12 3.614458 3.614458 4 25 15 4.819277 4.819277 .. ... ... ... ... 79 400 240 95.180723 95.180723 80 405 243 96.385542 96.385542 81 410 246 97.590361 97.590361 82 415 249 98.795181 98.795181 83 420 252 100.000000 100.000000 [84 rows x 4 columns]
Interpolating the values
Next, the values are interpolated. To my understanding, this is like cross-referencing the values in one list against the values in another. It’s like creating an array with floating-point indexes. The values in between are interpolated and rounded to the nearest mm. The resulting values are consistently approximate.
scaled_paper_height = math.floor(np.interp(95.2, scaled_heights, possible_heights_list)) scaled_paper_width = math.floor(np.interp(95.2, scaled_widths, possible_widths_list)) print(scaled_paper_width) print(scaled_paper_height)
400 240
Notice that the printed values correspond to the scaled values in the DataFrame. It’s best if the user can determine the scale to crop the paper to. So, the first argument to np.interp is replaced with args.scale[0].
scaled_paper_height = math.floor(np.interp(args.scale[0], scaled_heights, possible_heights_list)) scaled_paper_width = math.floor(np.interp(args.scale[0], scaled_widths, possible_widths_list))
Writing to a file
The output of the script is code which can be understood by the ConTeXt typesetting software. F-strings containing the values calculated by or provided to the script are used. The variables feature at key points in the ConTeXt code. The file is created. Then, a blank layout is defined and setup.
f = open(args.outfile[0], "w")
f.write("""\\definelayout[blank][
topspace=0mm,
backspace=0mm,
bottomspace=0mm,
width=fit,
height=fit,
header=0mm,
footer=0mm,
leftmargin=0mm,
rightmargin=0mm,
leftmargindistance=0mm,
rightmargindistance=0mm]
\\setuplayout[blank]""")
Then, having turned off page numbering, the f-string containing the values of scaled_paper_width and scaled_paper_height are passed to \definepapersize.
f.write(f"""\\definepapersize[scaled][width={scaled_paper_width}mm, height={scaled_paper_height}mm]
\\setuppapersize[scaled]""")
The code takes landscape mode into account using an if statement
if "portrait" in args.orientation:
f.write(f"[{args.papersize[0]}]")
else:
f.write(f"[{args.papersize[0]}, landscape]")
Finally, the layout is setup, the frame is switched on and the text environment is invoked. Inside the text environment, a frame which fills the typesetting area is included to ensure there is content in the document.
f.write("""\\setuplayout[location=""" "{middle,middle}" """,marking=empty]
\\showframe
\\starttext
\\startframedtext[width=\\textwidth,height=\\textheight]
\\stopframedtext
\\stoptext
""")
f.close()
PDF Output
ConTeXt can be run on the output file, in this case main.tex, to produce a pdf.
