Class: Preflight::Rules::MinPpi

Inherits:
Object
  • Object
show all
Includes:
Measurements
Defined in:
lib/preflight/rules/min_ppi.rb

Overview

For high quality prints, you generally want raster images to be AT LEAST 300 points-per-inch (ppi). 600 is better, 1200 better again.

Defined Under Namespace

Classes: Point

Constant Summary collapse

DEFAULT_GRAPHICS_STATE = 
{
  :ctm => Matrix.identity(3)
}

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(min_ppi) ⇒ MinPpi

Returns a new instance of MinPpi.



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# File 'lib/preflight/rules/min_ppi.rb', line 21

def initialize(min_ppi)
  @min_ppi = min_ppi.to_i
  @messages = []
  @page_num = 0
end

Instance Attribute Details

#messages ⇒ Object (readonly)

Returns the value of attribute messages.



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# File 'lib/preflight/rules/min_ppi.rb', line 19

def messages
  @messages
end

Instance Method Details

#begin_page(hash = {}) ⇒ Object

start fresh on every page



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# File 'lib/preflight/rules/min_ppi.rb', line 90

def begin_page(hash = {})
  @images = {}
  @page_num += 1
  @stack = [DEFAULT_GRAPHICS_STATE]
end

#concatenate_matrix(*args) ⇒ Object

update the current transformation matrix.

If the CTM is currently undefined, just store the new values.

If there’s an existing CTM, then multiple the existing matrix with the new matrix to form the updated matrix.



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# File 'lib/preflight/rules/min_ppi.rb', line 57

def concatenate_matrix(*args)
  transform = Matrix[
    [args[0], args[1], 0],
    [args[2], args[3], 0],
    [args[4], args[5], 1]
  ]
  if state[:ctm]
    state[:ctm] = transform * state[:ctm]
  else
    state[:ctm] = transform
  end
end

#invoke_xobject(label) ⇒ Object

As each image is drawn on the canvas, determine the amount of device space it’s being crammed into and therefore the PPI.



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# File 'lib/preflight/rules/min_ppi.rb', line 73

def invoke_xobject(label)
  return unless @images[label]

  sample_w, sample_h = *@images[label]
  device_w = pt2in(image_width)
  device_h = pt2in(image_height)

  horizontal_ppi = (sample_w / device_w).round(3)
  vertical_ppi   = (sample_h / device_h).round(3)

  if horizontal_ppi < @min_ppi || vertical_ppi < @min_ppi
    @messages << "Image with low PPI/DPI on page #{@page_num} (h:#{horizontal_ppi} v:#{vertical_ppi})"
  end
end

#resource_xobject(label, stream) ⇒ Object

store sample width and height for each image on the current page



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# File 'lib/preflight/rules/min_ppi.rb', line 41

def resource_xobject(label, stream)
  return unless stream.hash[:Subtype] == :Image

  @images[label] = [
    stream.hash[:Width],
    stream.hash[:Height]
  ]
end

#restore_graphics_state ⇒ Object 



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# File 'lib/preflight/rules/min_ppi.rb', line 31

def restore_graphics_state
  @stack.pop
end

#save_graphics_state ⇒ Object 



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# File 'lib/preflight/rules/min_ppi.rb', line 27

def save_graphics_state
  @stack.push clone_state
end

#state ⇒ Object 



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# File 'lib/preflight/rules/min_ppi.rb', line 35

def state
  @stack.last
end