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JPEG image with alpha channel on website


JPEG image with alpha channel on website

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JPEG image with alpha channel on website
Tag : development , By : Tim Coffman
Date : January 10 2021, 01:57 PM


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Convert alpha channel in white when saving to JPEG with ImageWriter


Tag : java , By : DotNetWise
Date : March 29 2020, 07:55 AM
this one helps. I'm converting a png image to jpeg with the following snippet of code: , My solution is ugly and probably slow, but it's a solution :)
    BufferedImage img = <your image>
    for( int i = 0; i < img.getWidth( ); i++ )
        for( int j = 0; j < img.getHeight( ); j++ ) {
            // get argb from pixel
            int coli = img.getRGB( i, j );
            int a = coli >> 24 & 0xFF;
            int r = coli >> 16 & 0xFF;
            int g = coli >> 8 & 0xFF;
            int b = coli & 0xFF;
            coli &= ~0xFFFFFFFF;
            // do what you want with a, r, g and b, in your case :
            a = 0xFF;
            // save argb
            coli |= a << 24;
            coli |= r << 16;
            coli |= g << 8;
            coli |= b << 0;
            img.setRGB( i, j, coli );
        }
    }

OpenCV 2.4 Jpeg to PNG with alpha channel


Tag : cpp , By : ZsA
Date : March 29 2020, 07:55 AM
To fix this issue I have a JPEG and a Mask. I want to create a PNG with the three JPEG channels and the alpha channel should be the Mask. How can I achieve this with OpenCV? , for your answer, I found a second solution:
cv::Mat transparent( height, width, CV_8UC4);
cv::Mat srcImg[] = {JPEG_img, alpha_Mask};
int from_to[] = { 0,0, 1,1, 2,2, 3,3 };
cv::mixChannels( srcImg, 2, &transparent, 1, from_to, 4 );

how to add an alpha channel of particular value in an BGR image


Tag : python , By : Dmitry
Date : March 29 2020, 07:55 AM
I think the issue was by ths following , Your code is actually correct.
The simple answer is that OpenCV's imshow() ignores transparency, so if you want to see its effect, save your image as a PNG/TIFF (both of which support transparency) and view it with a different viewer - such as GIMP, Photoshop or feh.
#!/usr/bin/env python3

import cv2
import numpy as np

def imshow(title,im):
    """Decorator for OpenCV "imshow()" to handle images with transparency"""

    # Check we got np.uint8, 2-channel (grey + alpha) or 4-channel RGBA image
    if (im.dtype == np.uint8) and (len(im.shape)==3) and (im.shape[2] in set([2,4])):

       # Pick up the alpha channel and delete from original
       alpha = im[...,-1]/255.0
       im = np.delete(im, -1, -1)

       # Promote greyscale image to RGB to make coding simpler
       if len(im.shape) == 2:
          im = np.stack((im,im,im))

       h, w, _ = im.shape

       # Make a checkerboard background image same size, dark squares are grey(102), light squares are grey(152)
       f = lambda i, j: 102 + 50*((i+j)%2)
       bg = np.fromfunction(np.vectorize(f), (16,16)).astype(np.uint8)

       # Resize to square same length as longer side (so squares stay square), then trim
       if h>w:
          longer = h
       else:
          longer = w
       bg = cv2.resize(bg, (longer,longer), interpolation=cv2.INTER_NEAREST)
       # Trim to correct size
       bg = bg[:h,:w]

       # Blend, using result = alpha*overlay + (1-alpha)*background
       im = (alpha[...,None] * im + (1.0-alpha[...,None])*bg[...,None]).astype(np.uint8)

    cv2.imshow(title,im)


if __name__ == "__main__":

    # Open RGBA image
    im = cv2.imread('paddington.png',cv2.IMREAD_UNCHANGED)

    imshow("Paddington (RGBA)",im)
    key = cv2.waitKey(0)
    cv2.destroyAllWindows()

    # Open Grey + alpha  image
    im = cv2.imread('paddington-ga.png',cv2.IMREAD_UNCHANGED)

    imshow("Paddington (grey + alpha)",im)
    key = cv2.waitKey(0)
    cv2.destroyAllWindows()

How to save an image as Tiff or PNG with an alpha channel or alpha mask in iPhone SDK?


Tag : iphone , By : Bin
Date : March 29 2020, 07:55 AM

Canvas with PNG + alpha channel to JPEG dataUrl


Tag : html , By : Milander
Date : March 29 2020, 07:55 AM
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