Python: Canvas drawing and rsCanvas module

by RS admin@robinsnyder.com : 1024 x 640

It is sometimes useful to create custom images in Python. The ImageDraw class in the PIL (Python Imaging Library) can be useful for this.

One can create new images or read and annotate existing images.

It as always useful to create a custom class. In this case, aggregation is used rather than inheritance.

In object-oriented terms, the approach of inheritance derives a class (i.e., subclasses) from an ancestor or parent class.

In object-oriented terms, the approach of aggregation make another class and instance variable and then controls access to that instance variable via it's own methods, properties, etc.

Some modules and classes will be created and used here.

For more information on basic module and class creation, see Matplotlib: DPI tricks and plot class and rsPlot module .

A custom canvas class in the rsCanvas module will now be created.

Some imports are needed.

import os
import PIL
from PIL import Image, ImageDraw, ImageFont

Some module variables are needed.

imagePos1 = 0
basePs1 = "./"

The variable imagePos1 allows a series of images to be created in order.

The variable basePs1 allows the base path of the saved images to be changed.

Some methods of the canvas class are now discussed.

The ImageDraw class uses colors are represented as a tuple of the integer values for red, green, and blue. I find it easier to work with the hex forms of red, green and blue.

color of "FF0000" returns (255,0,0)
color of "00FF00" returns (0,255,0)
color of "0000FF" returns (0,0,255)

The color method converts from hex to tuple representation.

def color(self, hex1):
	r1 = int(hex1[0:2],16)
	g1 = int(hex1[2:4],16)
	b1 = int(hex1[4:6],16)
	return (r1,g1,b1)

The initializer sets various instance variables which can then be changed by the calling routines as needed.

def __init__(self, stub1, width1=640, height1=480, back1="FFFFFF"):
	stub1 = stub1
	width1 = width1
	height1 = height1
	back1 = back1
	thick1 = 1
	fill1 = "FF0000"
	edge1 = "FF0000"
	image1 = Image.new("RGB",(self.width1,self.height1),self.color(self.back1))
	draw1 = ImageDraw.Draw(image1)
	fontSet1()
	moveto(width1 / 2, height1 / 2)

Important parts:

The width and height are set.
The default colors are set, as is the default thickness.
An image image1 is created as the canvas (width, height, and back are required).
A drawing object draw1 is created.
The position is set to the center of the image.

Note: Some defaults are set, where possible, using an existing instance method.

def moveto(self, x2, y2):
	x1 = x2
	y1 = y2

def lineto(self, x2, y2):
	draw1.line((x1,y1,x2,y2),fill=color(fill1),width=thick1)
	x1 = x2
	y1 = y2

An ImageFont object is required to draw text. This is saved in the font1 instance variable.

def fontSet1(self, fontName1="arial.ttf", fontSize1=32, fontColor1="000000"):
	fontName1 = fontName1
	fontSize1 = fontSize1
	fontColor1 = color(fontColor1)
	font1 = ImageFont.truetype(fontName1,size=fontSize1)

def text(self, text1):
	draw1.text((x1,y1),text1,fill=fontColor1,font=font1)

A method similar to the one used in the rsPlot module is used here to save the canvas
as an image.

def save(self, type1="png"):
	type1 = type1
	global imagePos1
	imagePos1 += 1
	saveFn1 = "{0:s}-0{1:d}".format(stub1,imagePos1)
	saveFt1 = "{0:s}".format(type1)
	saveFs1 = "{0:s}{1:s}.{2:s}".format(basePs1,saveFn1,saveFt1)
	image1.save(saveFs1)
	savedImage1 = Image.open(saveFs1)
	savedWidth1, savedHeight1= savedImage1.size
	(_, _, _, _, _, _, savedSize1, _, savedTime1, _) = os.stat(saveFs1)
	print("\t{0:s} : {1:d} x {2:d} , {3:,} bytes".format(saveFs1,savedWidth1,savedHeight1,savedSize1))

Here is a code module in Lua [module rsCanvas in rsCanvas.py].

# module rsCanvas.py
import os
import PIL
from PIL import Image, ImageDraw, ImageFont
imagePos1 = 0
basePs1 = "./"
class canvas():
	def color(self, hex1):
		r1 = int(hex1[0:2],16)
		g1 = int(hex1[2:4],16)
		b1 = int(hex1[4:6],16)
		return (r1,g1,b1)
	def __init__(self, stub1, width1=640, height1=480, back1="FFFFFF"):
		stub1 = stub1
		width1 = width1
		height1 = height1
		back1 = back1
		thick1 = 1
		fill1 = "FF0000"
		edge1 = "FF0000"
		image1 = Image.new("RGB",(self.width1,self.height1),self.color(self.back1))
		draw1 = ImageDraw.Draw(image1)
		fontSet1()
		moveto(width1 / 2, height1 / 2)
	def save(self, type1="png"):
		type1 = type1
		global imagePos1
		imagePos1 += 1
		saveFn1 = "{0:s}-0{1:d}".format(stub1,imagePos1)
		saveFt1 = "{0:s}".format(type1)
		saveFs1 = "{0:s}{1:s}.{2:s}".format(basePs1,saveFn1,saveFt1)
		image1.save(saveFs1)
		savedImage1 = Image.open(saveFs1)
		savedWidth1, savedHeight1= savedImage1.size
		(_, _, _, _, _, _, savedSize1, _, savedTime1, _) = os.stat(saveFs1)
		print("\t{0:s} : {1:d} x {2:d} , {3:,} bytes".format(saveFs1,savedWidth1,savedHeight1,savedSize1))
	def fontSet1(self, fontName1="arial.ttf", fontSize1=32, fontColor1="000000"):
		fontName1 = fontName1
		fontSize1 = fontSize1
		fontColor1 = color(fontColor1)
		font1 = ImageFont.truetype(fontName1,size=fontSize1)
	def text(self, text1):
		draw1.text((x1,y1),text1,fill=fontColor1,font=font1)
	def moveto(self, x2, y2):
		x1 = x2
		y1 = y2
	def lineto(self, x2, y2):
		draw1.line((x1,y1,x2,y2),fill=color(fill1),width=thick1)
		x1 = x2
		y1 = y2
print("(module rsCanvas imported)")

Here is the Python code [#11]

import rsCanvas
stub1 = "draw21-11"
width1 = 256
height1 = 256
canvas1 = rsCanvas.canvas(stub1,width1,height1)
margin1 = 10
fill1 = canvas1.color("FFFFFF")
outline1 = canvas1.color("FF0000")
canvas1.back1 = "CCCCCC"
box1 = (margin1,margin1,width1-margin1,height1-margin1)
# rectangle, ellipse, arc, circle have not yet been abstracted
canvas1.draw1.rectangle(box1,outline=outline1,fill=fill1,width=4)
outline1 = canvas1.color("0000FF")
fill1 = canvas1.color("CCCCCC")
canvas1.draw1.ellipse(box1,outline=outline1,fill=fill1,width=4)
canvas1.moveto(40,50)
canvas1.text("Hello, World")
canvas1.thick1 = 4
canvas1.moveto(40,100)
canvas1.lineto(200,100)
canvas1.save()

Here is the output of the Python code.

(module rsCanvas imported)

Some capabilities not shown here include the following.

Blurring an image
Cropping an image
Putting an existing image in part of another image
Copying (and saving) part of an image
Rotating an image

by RS admin@robinsnyder.com : 1024 x 640