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Pygame change image colour but preserve transparency

I've got a function that takes an image and adjusts all of the RGB values by a given amount:
def colour(self,img,col):
img = self.my_image.copy()
col = (col[0],col[1],col[2],0)
img.fill(col, None, pygame.BLEND_RGBA_ADD)
return img
I want to apply this to a partially transparent image. But when I apply this to the image, the transparent pixels become coloured. I want these pixels to stay transparent, but any opaque pixels to be coloured as normal. Is there any way I can do this, without having to loop through every pixel and check if each one is transparent before adjusting it? Thanks

fill treats the color to be solid. You have to use blit.
Create a transparent image the size of the source image and fill it with the color. Finally, mix both images:
def colour(self, img, col):
img = self.my_image.copy()
color_img = pygame.Surface(img.get_size(), pygame.SRCALPHA)
color_img.fill((col[0], col[1], col[2], 0))
img.blit(color_img, (0, 0), special_flags = pygame.BLEND_RGBA_ADD)
return img
See also Is it possible to change sprite colours in Pygame?

Using Python Pillow to 'Punch' Out transparency Using Second Image

I am currently trying to use an RGBA image to 'punch' out a hole in another RGBA image but all my current attempts have failed to maintain the original transparency. Once I apply an alpha channel using putalpha it will replace the original alpha channel completely and turn previously transparent pixels back to their original colors.
I am trying to perform a "putalpha" on only the pixels with 100% transparency.
In the photos below I attempt to overlap an 'inverted transparency' alpha channel on top of my Circle to perform the 'punch out'. Instead of only applying the transparent pixels it will replace the entire image's alpha which turns the rest of the circle image's transparency white.
Is there a way for me to do this transparency "Merge" to achieve an alpha layer that is a composite of both images?
#image2 is a square, image1 is a circle
# swapTransparency is a function I made that works in swapping the transparency, it just goes pixel by pixel and switches alpha channel value to # max where empty and to 0 everywhere else.
# probably a better and more effective way to invert the transparency but this works right now and might not even be needed.
def swapTransparency(img):
datas = img.getdata()
newData = []
for item in datas:
if item [3] == 0:
newData.append((0, 0, 0, 255))
else:
newData.append((255, 255, 255, 0))
img.putdata(newData)
return img
##This is putting alpha channel overtop but its replacing the entire alpha instead of merging them, losing original cricle transparency.
image2 = swapTransparency(image2)
alphaChannel = image2.getchannel('A')
image1.putalpha(image2)
Image1
Image2
Desired Results

How to replace color for colored objects in image?

I am trying to detect edges in images of a video, but edge detection methods such as canny does not work very well might be due to in similarity between boxes's color and floor color or brightness so I want to find a way to make all red and blue boxes look as white as possible, or may be the best way to detect edges as perfect as possible for every frame since that is the ultimate goal.

I recommend you using color tracking then.
Convert to HSV
cv2.bgr2hsv
Why hsv? eventhough the brightness change, u can still detect that color
Filtering
You can use cv2.inrange
Noise cancelling
Use cv2.Gaussianblur
Contouring
use cv2.findContours
Find the edge
use ur method
Repeat this step for every color of your box
Hope this help

Just to complete my comment in your question. One can use HSV/HLS colorspaces and use inRanges with the Hue channel. For example:
import numpy as np
import cv2
# load image and threshold it
original = cv2.imread("a.jpg")
hsvframe = cv2.cvtColor(original, cv2.COLOR_BGR2HLS)
mask = cv2.inRange(hsvframe, (160,40,40), (180, 255, 255))
mask = mask + cv2.inRange(hsvframe, (0,40,40), (12, 255, 255)) # color red is at the beginning and end of the hue wheel
original[mask==255] = (0,255,0)
cv2.imshow("image", original)
cv2.waitKey(0)
cv2.destroyAllWindows()
Things to remember, Hue goes from 0-180 in np.uint8. This means if you need hue 300-360 the limits will be 150-180. The other two values are 0-255 where 255 = 100%.
The result of this small code is:
It is not perfect, but one can refine it using the methods suggested by the other answer. I hope this helps.

HTML5 canvas source-atop alternative in PIL

I cannot find the right function to add color overlay on another image when transparent areas should remain untouched.
For example on source image there is a semi-transparent white circle and around it everything is fully transparent. When I apply the operation with red color, I'd like to get white/red circle with fully transparent area around it.
On HTML5 canvas, it is achieved by:
layerContext.globalCompositeOperation = "source-atop";
layerContext.fillStyle = color;
layerContext.fillRect(0, 0, w, h);
I tried alpha_composite, blend and composite functions, but maybe misused them.
EDIT: here is what I get using:
overlay = Image.new('RGB', im1.size, (255, 0, 0))
im1.paste(overlay, mask=im1)
Canvas:
PIL:
PIL result is a little bit lighter, but color is the same. Any ideas?

Python: Combining images using paste with overlapping pixels and areas with alpha channel=0

I am trying to combine three images together. The image I want on the bottom is a 700x900 image with all black pixels. On top of that I want to paste an image that is 400x400 with an offset of 100,200. On top of that I want to paste an image border that is 700x900. The image border has alpha=0 in the inside of it and alpha=0 around it because it doesn't have straight edges. When I run the code I have pasted below I encounter 2 problems:
1) Everywhere on the border image where the alpha channel = 0, the alpha channel has been set to 255 and the color white shows instead of the black background and the image I am putting the border around.
2) The border image's quality has been significantly reduced and looks a lot different than it should.
Also: part of the border image will cover part of the Image I am putting the border around. So I can't just switch the order that I am pasting.
Thanks in advance for any help.
#!/usr/bin/python -tt
from PIL import ImageTk, Image
old_im2 = Image.open('backgroundImage1.jpg') # size = 400x400
old_im = Image.open('topImage.png') # size = 700x900
new_size = (700,900)
new_im = Image.new("RGBA", new_size) # makes the black image
new_im.paste(old_im2, (100, 200))
new_im.paste(old_im,(0,0))
new_im.show()
new_im.save('final.jpg')

I think you have a misconception about images - the border image does have pixels everywhere. It's not possible for it to be "missing" pixels. It is possible to have an image with an alpha channel, which is a channel like the R, G, and B channels, but indicates transparency.
Try this:
1. Make sure that topImage.png has a transparency channel, and that the pixels that you want to be "missing" are transparent (i.e. have a maximum alpha value). You can double check this way:
print old_im.mode # This should print "RGBA" if it has an alpha channel.
2. Create new_im in "RGBA" mode:
new_im = Image.new("RGBA", new_size) # makes the black image
# Note the "A" --------^
3. Try this paste statement instead:
new_im.paste(old_im,(0,0), mask=old_im) # Using old_im as the mask argument should tell the paste function to use old_im's alpha channel to combine the two images.