Please bear with me, I've only started python a few weeks ago.
I am using JES.
I have made a function to convert a picture to grayscale. I created two names for each color r and r1, g and g1, b and b1. The idea behind this, was to keep the original values in memory, so the picture could be restored to it's original color.
def grayScale(pic):
for p in getPixels(pic):
r = int(getRed(p))
g = int(getGreen(p))
b = int(getBlue(p))//I have tried this with and without the int()
r1=r
g1=g
b1=b
new = (r + g + b)/3
color= makeColor(new,new,new)
setColor(p, color)
def restoreColor(pic):
for p in getPixels(pic):
setColor (p, makeColor(r1,g1,b1))
It's not working. The error: "local or global name could not be found."
I understand why I am getting this error.
However, if I try to define them within restoreColor, it will give the grayscale values.
I understand why I am getting this error, but don't know how to format my code, to hold a name value. I have looked at questions about local and global variables/names; but I cannot work out, within the rudimentary syntax I have learnt, how to do this.
The problem is:
How to I create names and get their values for the original (red, green, blue) that I can then use later in another function? Everything I have tried, has returned the altered (grayscale) values. thnx
Just to add an "artistic" point of view:
You are using (r + g + b) / 3 in your program, but there is other algorithms:
1) The lightness method
averages the most prominent and least prominent colors:
(max(R, G, B) + min(R, G, B)) / 2
2) The average method
(yours) simply averages the values:
(R + G + B) / 3
3) The luminosity method
is a more sophisticated version of the average method. It also averages the values, but it forms a weighted average to account for human perception. We’re more sensitive to green than other colors, so green is weighted most heavily. The formula for luminosity is:
0.21 R + 0.71 G + 0.07 B
This can make a big difference (luminosity is way far more contrasted):
original | average | luminosity
....................................................
Code :
px = getPixels(pic)
level = int(0.21 * getRed(px) + 0.71 * getGreen(px) + 0.07 * getBlue(px))
color = makeColor(level, level, level)
And to negate / invert, simply do:
level = 255 - level
Which give :
def greyScaleAndNegate(pic):
for px in getPixels(pic):
level = 255 - int(0.21*getRed(px) + 0.71*getGreen(px) +0.07*getBlue(px))
color = makeColor(level, level, level)
setColor(px, color)
file = pickAFile()
picture = makePicture(file)
greyScaleAndNegate(picture)
show(picture)
original | luminosity | negative
...................................................................