PIL 中的 PNG 图像质量

Question

Have been trying to upload the following png file to google cloud storage through app engine:

Before the upload, I'm running this through PIL to take care of any image rotations or changes in background color etc

However, I'm getting really bad image quality when running PIL manipulations through the app even though running the same commands in python command line comes out fine

Anybody have ideas?

For the PIL commands, I'm just running the following:

imtemp = Image.open('/[path]/logo.png')
size = max(imtemp.size[0],imtemp.size[1]) 
im = Image.new('RGBA', (size,size), (255,255,255,0))
im.paste(imtemp, ((size-imtemp.size[0])/2,(size-imtemp.size[1])/2)) 
imtemp = im 
im = Image.new('RGB', (size,size), '#FFFFFF') 
im.paste(imtemp, (0,0), imtemp) 
im.show()

Have tried below, but still no luck

    imtemp = Image.open(StringIO(imagedata)).convert("RGBA")
    im = Image.new("RGB", imtemp.size, "#FFFFFF")
    im.paste(imtemp, None, imtemp)
    imageoutput = StringIO()
    im.save(imageoutput, format="PNG", quality=85, optimize=True, progressive=True)
    imageoutput = imageoutput.getvalue()

Answer 1

It looks like you want to take a palettized image, possibly with transparent pixels, project it on a white background and make a quality-resized version of it which is half as big.

You can use the convert() and thumbnail() function for this:

from PIL import Image

# Open the image and convert it to RGBA.
orig = Image.open("fresh.png").convert("RGBA")

# Paste it onto a white background.
im = Image.new("RGB", orig.size, "#ffffff")
im.paste(orig, None, orig)

# Now a quality downsize.
w, h = im.size
im.thumbnail((w / 2, h / 2), Image.ANTIALIAS)
im.show()    

Of course, you can leave the thumbnail() call out if you want the image at the original size.