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I am trying to use the Pillow (python-imaging-library) Python library in order to create an outline/stroke/border (with any color and width chosen) around my .png image. You can see here the original image and my wanted result (create by a phone app):
https://i.stack.imgur.com/4x4qh.png
You can download the png file of the original image here: https://pixabay.com/illustrations/brain-character-organ-smart-eyes-1773885/
I have done it in the medium size(1280x1138) but maybe it is better to do it with the smallest size (640x569).
I tried to solve the problem with two methods.
METHOD ONE
The first method is to create a fully blacked image of the brain.png image, enlarge it, and paste the original colored brain image on top of it. Here is my code:
brain_black = Image.open("brain.png") #load brain image
width = brain_black.width #in order not to type a lot
height = brain_black.height #in order not to type a lot
rectangle = Image.new("RGBA", (width, height), "black") #creating a black rectangle in the size of the brain image
brain_black.paste(rectangle, mask=brain_black) #pasting on the brain image the black rectangle, and masking it with the brain picture
#now brain_black is the brain.png image, but all its pixels are black. Let's continue:
brain_black = brain_black.resize((width+180, height+180)) #resizing the brain_black by some factor
brain_regular = Image.open("brain.png") #load the brain image in order to paste later on
brain_black.paste(brain_regular,(90,90), mask=brain_regular) #paste the regular (colored) brain on top of the enlarged black brain (in x=90, y=90, the middle of the black brain)
brain_black.save("brain_method_resize.png") #saving the image
This method doesn't work, as you can see in the image link above. It might have worked for simple geometric shapes, but not for a complicated shape like this.
METHOD TWO
The second method is to load the brain image pixels data into a 2-dimensional array, and loop over all of the pixels. Check the color of every pixel, and in every pixel which is not transparent (means A(or Alpha) is not 0 in the rgbA form) to draw a black pixel in the pixel above, below, right, left, main diagonal down, main diagonal up, secondary diagonal (/) down and secondary diagonal (/) up. Then to draw a pixel in the second pixel above, the second pixel below and etc. this was done with a "for loop" where the number of repetitions is the wanted stroke width (in this example is 30). Here is my code:
brain=Image.open("brain.png") #load brain image
background=Image.new("RGBA", (brain.size[0]+400, brain.size[1]+400), (0, 0, 0, 0)) #crate a background transparent image to create the stroke in it
background.paste(brain, (200,200), brain) #paste the brain image in the middle of the background
pixelsBrain = brain.load() #load the pixels array of brain
pixelsBack=background.load() #load the pixels array of background
for i in range(brain.size[0]):
for j in range(brain.size[1]):
r, c = i+200, j+200 #height and width offset
if(pixelsBrain[i,j][3]!=0): #checking if the opacity is not 0, if the alpha is not 0.
for k in range(30): #the loop
pixelsBack[r, c + k] = (0, 0, 0, 255)
pixelsBack[r, c - k] = (0, 0, 0, 255)
pixelsBack[r + k, c] = (0, 0, 0, 255)
pixelsBack[r - k, c] = (0, 0, 0, 255)
pixelsBack[r + k, c + k] = (0, 0, 0, 255)
pixelsBack[r - k, c - k] = (0, 0, 0, 255)
pixelsBack[r + k, c - k] =(0, 0, 0, 255)
pixelsBack[r - k, c + k] = (0, 0, 0, 255)
background.paste(brain, (200,200), brain) #pasting the colored brain onto the background, because the loop "destroyed" the picture.
background.save("brain_method_loop.png")
This method did work, but it is very time-consuming (takes about 30 seconds just for one picture and 30 pixels stroke). I want to do it for many pictures so this method is not good for me.
Is there an easier and better way to reach my wanted result using Python Pillow library. How can I do it?
And also, how can I fasten my loop code (I understood something about Numpy and OpenCV, which is better for this purpose?)
I know that if a phone app could do it in a matter of milliseconds, also python can, but I didn't find any way to do it.
Thank you.
I tried some solution similar with photoshop stroke effect using OpenCV (It is not perfect and I still finding better solution)
This algorithm is based on euclidean distance transform. I also tried dilation algorithm with ellipse kernel structure, it is bit different with photoshop, and there are some information that distance transform is the way that photoshop using.
def stroke(origin_image, threshold, stroke_size, colors):
img = np.array(origin_image)
h, w, _ = img.shape
padding = stroke_size + 50
alpha = img[:,:,3]
rgb_img = img[:,:,0:3]
bigger_img = cv2.copyMakeBorder(rgb_img, padding, padding, padding, padding,
cv2.BORDER_CONSTANT, value=(0, 0, 0, 0))
alpha = cv2.copyMakeBorder(alpha, padding, padding, padding, padding, cv2.BORDER_CONSTANT, value=0)
bigger_img = cv2.merge((bigger_img, alpha))
h, w, _ = bigger_img.shape
_, alpha_without_shadow = cv2.threshold(alpha, threshold, 255, cv2.THRESH_BINARY) # threshold=0 in photoshop
alpha_without_shadow = 255 - alpha_without_shadow
dist = cv2.distanceTransform(alpha_without_shadow, cv2.DIST_L2, cv2.DIST_MASK_3) # dist l1 : L1 , dist l2 : l2
stroked = change_matrix(dist, stroke_size)
stroke_alpha = (stroked * 255).astype(np.uint8)
stroke_b = np.full((h, w), colors[0][2], np.uint8)
stroke_g = np.full((h, w), colors[0][1], np.uint8)
stroke_r = np.full((h, w), colors[0][0], np.uint8)
stroke = cv2.merge((stroke_b, stroke_g, stroke_r, stroke_alpha))
stroke = cv2pil(stroke)
bigger_img = cv2pil(bigger_img)
result = Image.alpha_composite(stroke, bigger_img)
return result
def change_matrix(input_mat, stroke_size):
stroke_size = stroke_size - 1
mat = np.ones(input_mat.shape)
check_size = stroke_size + 1.0
mat[input_mat > check_size] = 0
border = (input_mat > stroke_size) & (input_mat <= check_size)
mat[border] = 1.0 - (input_mat[border] - stroke_size)
return mat
def cv2pil(cv_img):
cv_img = cv2.cvtColor(cv_img, cv2.COLOR_BGRA2RGBA)
pil_img = Image.fromarray(cv_img.astype("uint8"))
return pil_img
output = stroke(test_image, threshold=0, stroke_size=10, colors=((0,0,0),))
I can't do a fully tested Python solution for you at the moment as I have other commitments, but I can certainly show you how to do it in a few milliseconds and give you some pointers.
I just used ImageMagick at the command line. It runs on Linux and macOS (use brew install imagemagick) and Windows. So, I extract the alpha/transparency channel and discard all the colour info. Then use a morphological "edge out" operation to generate a fat line around the edges of the shape in the alpha channel. I then invert the white edges so they become black and make all the white pixels transparent. Then overlay on top of the original image.
Here's the full command:
magick baby.png \( +clone -alpha extract -morphology edgeout octagon:9 -threshold 10% -negate -transparent white \) -flatten result.png
So that basically opens the image, messes about with a cloned copy of the alpha layer inside the parentheses and then flattens the black outline that results back onto the original image and saves it. Let's do the steps one at a time:
Extract the alpha layer as alpha.png:
magick baby.png -alpha extract alpha.png
Now fatten the edges, invert and make everything not black become transparent and save as overlay.png:
magick alpha.png -morphology edgeout octagon:9 -threshold 10% -negate -transparent white overlay.png
Here's the final result, change the octagon:9 to octagon:19 for fatter lines:
So, with PIL... you need to open the image and convert to RGBA, then split the channels. You don't need to touch the RGB channels just the A channel.
im = Image.open('baby.png').convert('RGBA')
R, G, B, A = im.split()
Some morphology needed here - see here.
Merge the original RGB channels with the new A channel and save:
result = Image.merge((R,G,B,modifiedA))
result.save('result.png')
Note that there are Python bindings to ImageMagick called wand and you may find it easier to translate my command-line stuff using that... wand. Also, scikit-image has an easy-to-use morphology suite too.
I've written this function which is based on morphological dilation and lets you set the stroke size and color. But it's EXTREMELY slow and it seems to not work great with small elements.
If anyone can help me speed it up it would be extremely helpful.
def addStroke(image,strokeSize=1,color=(0,0,0)):
#Create a disc kernel
kernel=[]
kernelSize=math.ceil(strokeSize)*2+1 #Should always be odd
kernelRadius=strokeSize+0.5
kernelCenter=kernelSize/2-1
pixelRadius=1/math.sqrt(math.pi)
for x in range(kernelSize):
kernel.append([])
for y in range(kernelSize):
distanceToCenter=math.sqrt((kernelCenter-x+0.5)**2+(kernelCenter-y+0.5)**2)
if(distanceToCenter<=kernelRadius-pixelRadius):
value=1 #This pixel is fully inside the circle
elif(distanceToCenter<=kernelRadius):
value=min(1,(kernelRadius-distanceToCenter+pixelRadius)/(pixelRadius*2)) #Mostly inside
elif(distanceToCenter<=kernelRadius+pixelRadius):
value=min(1,(pixelRadius-(distanceToCenter-kernelRadius))/(pixelRadius*2)) #Mostly outside
else:
value=0 #This pixel is fully outside the circle
kernel[x].append(value)
kernelExtent=int(len(kernel)/2)
imageWidth,imageHeight=image.size
outline=image.copy()
outline.paste((0,0,0,0),[0,0,imageWidth,imageHeight])
imagePixels=image.load()
outlinePixels=outline.load()
#Morphological grayscale dilation
for x in range(imageWidth):
for y in range(imageHeight):
highestValue=0
for kx in range(-kernelExtent,kernelExtent+1):
for ky in range(-kernelExtent,kernelExtent+1):
kernelValue=kernel[kx+kernelExtent][ky+kernelExtent]
if(x+kx>=0 and y+ky>=0 and x+kx<imageWidth and y+ky<imageHeight and kernelValue>0):
highestValue=max(highestValue,min(255,int(round(imagePixels[x+kx,y+ky][3]*kernelValue))))
outlinePixels[x,y]=(color[0],color[1],color[2],highestValue)
outline.paste(image,(0,0),image)
return outline
Very simple and primitive solution: use PIL.ImageFilter.FIND_EDGES to find edge of drawing, it is about 1px thick, and draw a circle in every point of the edge. It is quite fast and require few libs, but has a disadvantage of no smoothing.
from PIL import Image, ImageFilter, ImageDraw
from pathlib import Path
def mystroke(filename: Path, size: int, color: str = 'black'):
outf = filename.parent/'mystroke'
if not outf.exists():
outf.mkdir()
img = Image.open(filename)
X, Y = img.size
edge = img.filter(ImageFilter.FIND_EDGES).load()
stroke = Image.new(img.mode, img.size, (0,0,0,0))
draw = ImageDraw.Draw(stroke)
for x in range(X):
for y in range(Y):
if edge[x,y][3] > 0:
draw.ellipse((x-size,y-size,x+size,y+size),fill=color)
stroke.paste(img, (0, 0), img )
# stroke.show()
stroke.save(outf/filename.name)
if __name__ == '__main__':
folder = Path.cwd()/'images'
for img in folder.iterdir():
if img.is_file(): mystroke(img, 10)
Solution using PIL
I was facing the same need: outlining a PNG image.
Here is the input image:
Input image
I see that some solution have been found, but in case some of you want another alternative, here is mine:
Basically, my solution workflow is as follow:
Read and fill the non-alpha chanel of the PNG image with the border
color
Resize the unicolor image to make it bigger
Merge the original image to the bigger unicolor image
Here you go! You have an outlined PNG image with the width and color of your choice.
Here is the code implementing the workflow:
from PIL import Image
# Set the border and color
borderSize = 20
color = (255, 0, 0)
imgPath = "<YOUR_IMAGE_PATH>"
# Open original image and extract the alpha channel
im = Image.open(imgPath)
alpha = im.getchannel('A')
# Create red image the same size and copy alpha channel across
background = Image.new('RGBA', im.size, color=color)
background.putalpha(alpha)
# Make the background bigger
background=background.resize((background.size[0]+borderSize, background.size[1]+borderSize))
# Merge the targeted image (foreground) with the background
foreground = Image.open(imgPath)
background.paste(foreground, (int(borderSize/2), int(borderSize/2)), foreground.convert("RGBA"))
imageWithBorder = background
imageWithBorder.show()
And here is the outputimage:
Output image
Hope it helps!
I found a way to do this using the ImageFilter module, it is much faster than any custom implementation that I've seen here and doesn't rely on resizing which doesn't work for convex hulls
from PIL import Image, ImageFilter
stroke_radius = 5
img = Image.open("img.png") # RGBA image
stroke_image = Image.new("RGBA", img.size, (255, 255, 255, 255))
img_alpha = img.getchannel(3).point(lambda x: 255 if x>0 else 0)
stroke_alpha = img_alpha.filter(ImageFilter.MaxFilter(stroke_radius))
# optionally, smooth the result
stroke_alpha = stroke_alpha.filter(ImageFilter.SMOOTH)
stroke_image.putalpha(stroke_alpha)
output = Image.alpha_composite(stroke_image, img)
output.save("output.png")
How fast change pixels values? In C# what i need to do is only use GetPixel() to get pixel value and SetPixel() to change it (its pretty easy to use but slow, MarshallCopy and Lock/UnlockBits is much faster).
In this code, i marking black pixels as 1 and white pixels as 0
import tkFileDialog
import cv2
import numpy as np
from matplotlib import pyplot as plt
path = tkFileDialog.askopenfilename()
bmp = cv2.imread(path) #reading image
height, width, channels = bmp.shape
if channels == 3:
bmp = cv2.cvtColor(bmp, cv2.COLOR_BGR2GRAY) #if image have 3 channels, convert to BW
bmp = bmp.astype('uint8')
bmp = cv2.adaptiveThreshold(bmp,255,cv2.ADAPTIVE_THRESH_GAUSSIAN_C,\
cv2.THRESH_BINARY,11,2) #Otsu thresholding
imageData = np.asarray(bmp) #get pixels values
pixelArray = [[0 for y in range(height)] for x in range(width)] #set size of array for pixels
for y in range(len(imageData)):
for x in range(len(imageData[0])):
if imageData[y][x] == 0:
pixelArray[y][x] = 1 #if black pixels = 1
else:
pixelArray[y][x] = 0 #if white pixels = 0
In c#, it can looks like this:
for (y = 0; y < bmp.Height-1; y++)
{
for (x = 0; x < bmp.Width-1; x++)
{
if (pixelArray[y, x] == 1)
newImage.SetPixel(x, y, Color.Black); //printing new bitmap
else
newImage.SetPixel(x, y, Color.White);
}
}
image2.Source = Bitmap2BitmapImage(newImage);
In the next step i will marking countour pixels as "2", but now i want to ask you, how to set new image in python from my specific value and then, display it? For experimental purpose, i want to invert image (from B&W to W&B) only by byte valuse. Can you help me how to do it?
EDIT1
I think i found a solution, but i have GREYSCALE image with one channel (i think thats how it works when i using cv2.cvtColor to convert 3 channels image to greyscale image). The function like this:
im[np.where((im == [0,0,0]).all(axis = 2))] = [0,33,166]
Could work pretty well, but how to make that function work with greyscale image? I want to set some black pixels (0) into White (255)
For a single channel image (gray scale image) use the following:
First create a copy of the gray image:
gray_2 = gray.copy()
Now assign black pixels to be white:
gray_2[np.where(gray == 0)] = 255
I am trying to get specific coordinates in an image. I have marked a red dot in the image at several locations to specify the coordinates I want to get. In GIMP I used the purist red I could find (HTML notation ff000). The idea was that I would iterate through the image until I found a pure shade of red and then print out the coordinates. I am using python and opencv to do so but I can't find any good tutorials (best I could find is this but it's not very clear...at least for me). Here is an example of the image I am dealing with.
I just want to know how to find the coordinates of the pixels with the red dots.
EDIT (added code):
import cv2
import numpy as np
img = cv2.imread('image.jpg')
width, height = img.shape[:2]
for i in range(0,width):
for j in range(0,height):
px = img[i,j]
I don't know what to do from here. I have tried code such as if px == [x,y,z] looking for color detection but that doesn't work.
You can do it with cv2 this way:
image = cv2.imread('image.jpg')
lower_red = np.array([0,0,220]) # BGR-code of your lowest red
upper_red = np.array([10,10,255]) # BGR-code of your highest red
mask = cv2.inRange(image, lower_red, upper_red)
#get all non zero values
coord=cv2.findNonZero(mask)
You can do this with PIL and numpy. I'm sure there is a similar implementation with cv2.
from PIL import Image
import numpy as np
img = Image.open('image.png')
width, height = img.size[:2]
px = np.array(img)
for i in range(height):
for j in range(width):
if(px[i,j,0] == 255 & px[i,j,1] == 0 & px[i,j,2] == 0):
print(i,j,px[i,j])
This doesn't work with the image you provided, since there aren't any pixels that are exactly (255,0,0). Something may have changed when it got compressed to a .jpg, or you didn't make them as red as you thought you did. Perhaps you could try turning off anti-aliasing in GIMP.
I have looked at tutorials, other stackoverflow questions and the PIL documentation itself, but I'm still still not sure how to do it.
I'd like to start fading an image vertically at approximately 55% down the y-axis, and have the image completely transparent at approximately 75%. It's important that I preserve the full height of the image, even though the last 25% or so should be completely transparent.
Is this possible to do with PIL?
Sure it's doable.
Let's assume that you're starting off with an image with no transparency (because otherwise, your question is ambiguous).
Step 1: Add an alpha plane. That's just putalpha, unless you're dealing with a non-planar image, in which case you'll need to convert it to RGB or L first.
Step 2: Iterate through the pixels you want to change by using the pixel array returned by load (or getpixel and setpixel if you have to deal with ancient versions of PIL).
Step 3: There is no step 3. Unless you count saving the image. In which case, OK, step 3 is saving the image.
from PIL import Image
im = Image.open('bird.jpg')
im.putalpha(255)
width, height = im.size
pixels = im.load()
for y in range(int(height*.55), int(height*.75)):
alpha = 255-int((y - height*.55)/height/.20 * 255)
for x in range(width):
pixels[x, y] = pixels[x, y][:3] + (alpha,)
for y in range(y, height):
for x in range(width):
pixels[x, y] = pixels[x, y][:3] + (0,)
im.save('birdfade.png')
Here the alpha drops off linearly from 255 to 0; it you want it to drop off according to a different curve, or you're using RGB16 instead of RGB8, or you're using L instead of RGB, you should be able to figure out how to change it.
If you want to do this faster, you can use numpy instead of a Python loop for step 2. Or you can reverse steps 1 and 2—construct an alpha plane in advance, and apply it all at once by passing it to putalpha instead of 255. Or… Since this took under half a second on the biggest image I had lying around, I'm not too worried about performance, unless you have to do a million of them and you want a faster version.
Using NumPy:
import numpy as np
import Image
img = Image.open(FILENAME).convert('RGBA')
arr = np.array(img)
alpha = arr[:, :, 3]
n = len(alpha)
alpha[:] = np.interp(np.arange(n), [0, 0.55*n, 0.75*n, n], [255, 255, 0, 0])[:,np.newaxis]
img = Image.fromarray(arr, mode='RGBA')
img.save('/tmp/out.png')
You have to change the code of #abarnert a bit if you want to fade image which already had a transparent background (detail):
from PIL import Image
im = Image.open('bird.jpg')
width, height = im.size
pixels = im.load()
for y in range(int(height*.55), int(height*.75)):
for x in range(width):
alpha = pixels[x, y][3]-int((y - height*.55)/height/.20 * 255) # change made here
if alpha <= 0:
alpha = 0
pixels[x, y] = pixels[x, y][:3] + (alpha,)
for y in range(y, height):
for x in range(width):
pixels[x, y] = pixels[x, y][:3] + (0,)
bg.save('birdfade.png')
I am trying to remove a certain color from my image however it's not working as well as I'd hoped. I tried to do the same thing as seen here Using PIL to make all white pixels transparent? however the image quality is a bit lossy so it leaves a little ghost of odd colored pixels around where what was removed. I tried doing something like change pixel if all three values are below 100 but because the image was poor quality the surrounding pixels weren't even black.
Does anyone know of a better way with PIL in Python to replace a color and anything surrounding it? This is probably the only sure fire way I can think of to remove the objects completely however I can't think of a way to do this.
The picture has a white background and text that is black. Let's just say I want to remove the text entirely from the image without leaving any artifacts behind.
Would really appreciate someone's help! Thanks
The best way to do it is to use the "color to alpha" algorithm used in Gimp to replace a color. It will work perfectly in your case. I reimplemented this algorithm using PIL for an open source python photo processor phatch. You can find the full implementation here. This a pure PIL implementation and it doesn't have other dependences. You can copy the function code and use it. Here is a sample using Gimp:
to
You can apply the color_to_alpha function on the image using black as the color. Then paste the image on a different background color to do the replacement.
By the way, this implementation uses the ImageMath module in PIL. It is much more efficient than accessing pixels using getdata.
EDIT: Here is the full code:
from PIL import Image, ImageMath
def difference1(source, color):
"""When source is bigger than color"""
return (source - color) / (255.0 - color)
def difference2(source, color):
"""When color is bigger than source"""
return (color - source) / color
def color_to_alpha(image, color=None):
image = image.convert('RGBA')
width, height = image.size
color = map(float, color)
img_bands = [band.convert("F") for band in image.split()]
# Find the maximum difference rate between source and color. I had to use two
# difference functions because ImageMath.eval only evaluates the expression
# once.
alpha = ImageMath.eval(
"""float(
max(
max(
max(
difference1(red_band, cred_band),
difference1(green_band, cgreen_band)
),
difference1(blue_band, cblue_band)
),
max(
max(
difference2(red_band, cred_band),
difference2(green_band, cgreen_band)
),
difference2(blue_band, cblue_band)
)
)
)""",
difference1=difference1,
difference2=difference2,
red_band = img_bands[0],
green_band = img_bands[1],
blue_band = img_bands[2],
cred_band = color[0],
cgreen_band = color[1],
cblue_band = color[2]
)
# Calculate the new image colors after the removal of the selected color
new_bands = [
ImageMath.eval(
"convert((image - color) / alpha + color, 'L')",
image = img_bands[i],
color = color[i],
alpha = alpha
)
for i in xrange(3)
]
# Add the new alpha band
new_bands.append(ImageMath.eval(
"convert(alpha_band * alpha, 'L')",
alpha = alpha,
alpha_band = img_bands[3]
))
return Image.merge('RGBA', new_bands)
image = color_to_alpha(image, (0, 0, 0, 255))
background = Image.new('RGB', image.size, (255, 255, 255))
background.paste(image.convert('RGB'), mask=image)
Using numpy and PIL:
This loads the image into a numpy array of shape (W,H,3), where W is the
width and H is the height. The third axis of the array represents the 3 color
channels, R,G,B.
import Image
import numpy as np
orig_color = (255,255,255)
replacement_color = (0,0,0)
img = Image.open(filename).convert('RGB')
data = np.array(img)
data[(data == orig_color).all(axis = -1)] = replacement_color
img2 = Image.fromarray(data, mode='RGB')
img2.show()
Since orig_color is a tuple of length 3, and data has
shape (W,H,3), NumPy
broadcasts
orig_color to an array of shape (W,H,3) to perform the comparison data ==
orig_color. The result in a boolean array of shape (W,H,3).
(data == orig_color).all(axis = -1) is a boolean array of shape (W,H) which
is True wherever the RGB color in data is original_color.
#!/usr/bin/python
from PIL import Image
import sys
img = Image.open(sys.argv[1])
img = img.convert("RGBA")
pixdata = img.load()
# Clean the background noise, if color != white, then set to black.
# change with your color
for y in xrange(img.size[1]):
for x in xrange(img.size[0]):
if pixdata[x, y] == (255, 255, 255, 255):
pixdata[x, y] = (0, 0, 0, 255)
You'll need to represent the image as a 2-dimensional array. This means either making a list of lists of pixels, or viewing the 1-dimensional array as a 2d one with some clever math. Then, for each pixel that is targeted, you'll need to find all surrounding pixels. You could do this with a python generator thus:
def targets(x,y):
yield (x,y) # Center
yield (x+1,y) # Left
yield (x-1,y) # Right
yield (x,y+1) # Above
yield (x,y-1) # Below
yield (x+1,y+1) # Above and to the right
yield (x+1,y-1) # Below and to the right
yield (x-1,y+1) # Above and to the left
yield (x-1,y-1) # Below and to the left
So, you would use it like this:
for x in range(width):
for y in range(height):
px = pixels[x][y]
if px[0] == 255 and px[1] == 255 and px[2] == 255:
for i,j in targets(x,y):
newpixels[i][j] = replacementColor
If the pixels are not easily identifiable e.g you say (r < 100 and g < 100 and b < 100) also doesn't match correctly the black region, it means you have lots of noise.
Best way would be to identify a region and fill it with color you want, you can identify the region manually or may be by edge detection e.g. http://bitecode.co.uk/2008/07/edge-detection-in-python/
or more sophisticated approach would be to use library like opencv (http://opencv.willowgarage.com/wiki/) to identify objects.
This is part of my code, the result would like:
source
target
import os
import struct
from PIL import Image
def changePNGColor(sourceFile, fromRgb, toRgb, deltaRank = 10):
fromRgb = fromRgb.replace('#', '')
toRgb = toRgb.replace('#', '')
fromColor = struct.unpack('BBB', bytes.fromhex(fromRgb))
toColor = struct.unpack('BBB', bytes.fromhex(toRgb))
img = Image.open(sourceFile)
img = img.convert("RGBA")
pixdata = img.load()
for x in range(0, img.size[0]):
for y in range(0, img.size[1]):
rdelta = pixdata[x, y][0] - fromColor[0]
gdelta = pixdata[x, y][0] - fromColor[0]
bdelta = pixdata[x, y][0] - fromColor[0]
if abs(rdelta) <= deltaRank and abs(gdelta) <= deltaRank and abs(bdelta) <= deltaRank:
pixdata[x, y] = (toColor[0] + rdelta, toColor[1] + gdelta, toColor[2] + bdelta, pixdata[x, y][3])
img.save(os.path.dirname(sourceFile) + os.sep + "changeColor" + os.path.splitext(sourceFile)[1])
if __name__ == '__main__':
changePNGColor("./ok_1.png", "#000000", "#ff0000")