Converting PNG to JPEG creates pixel noise in the background-CodePudding

I have to convert some PNGs with transparent bg to simple JPEGs where the transparent background turns to white (which I assumed will happen by default). I have tried all of the solutions I could find here, but after saving the PNG as JPEG the image will look like this: (the noisy area was transparent on the PNG and the black was drop shadow)

Converted image

Original image

This is the code I use:

# save the PNG 
response = requests.get(image_url, headers = header)
file = open("%s-%s.png" % (slug, item_id,), "wb")
file.write(response.content)
file.close()

# open the PNG and save as a JPEG
im1 = Image.open(filepath_to_png)
rgb_im = im1.convert('RGB')
rgb_im.mode
rgb_im.save(filepath_normal)

My question is that how could I prevent the JPEG to have that corrupted background? My goal is just simply have the same image in JPEG what I had in PNG.

CodePudding user response：

The method you are using to convert to RGB would work on some images that just require straight-forward conversion like the ones with hard-edged transparency masks, but for those with soft-edged masking (like the transparency shadows in your image) it is not be effective as the conversion does not know how to deal with that semi-transparency.

A better approach to handle this would be to create a new Image with the same dimensions and fill it with a white background, then you just need to paste your original image:

new_im = Image.new( "RGB", im1.size, ( 255,255,255 ) )
new_im.paste( im1, im1 )
new_im.save( filepath_normal )

I have tested this approach using an image with soft-edged masking and obtained the following

from PIL import Image
im = Image.open("1.png")
bg = Image.new("RGB", im.size, (255,255,255))
bg.paste(im,im)
bg.save("2.jpg")

Result I got had transparent background turned to white.