Watermark with sharp

Question

I have a image and i put watermark there, but i want that watermark hs a opacity like 30%.

My code:

    let sharp = require('sharp');
    let buffer = null;

    await sharp(image)
        .composite([{ input: './logo.png', gravity: 'center' }])
        .sharpen()
        .withMetadata()
        .toBuffer()
        .then(function(outputBuffer) {
            buffer = outputBuffer;
        });
    return buffer;

How can i say that logo has opacity like 30%?

I believe you would need to composite another image which just has an alpha channel at 0.7, and use blend mode "dest-in" — WilliamNHarvey, Jul 23 '19 at 19:45
@Asthmatic Sorry i didnt understod. can you pass a example code? — Guilherme Monteiro de Oliveira, Jul 23 '19 at 20:05
something like https://github.com/lovell/sharp/issues/405#issuecomment-208033263 but set the blend mode to `dest-in`... but in your case you don't need a reducer because it would just be 2 images — WilliamNHarvey, Jul 23 '19 at 20:21
@Asthmatic I do that and all image be black, and watermark was 0% of opacity — Guilherme Monteiro de Oliveira, Jul 23 '19 at 20:33

score 0 · Answer 1 · answered Aug 31 '21 at 04:38

0

Your need to change the opacity of "logo.png" use blur, then compose it like code snipp above.

answered Aug 31 '21 at 04:38

Ngoc Bui

56
1

score -3 · Accepted Answer · answered Jul 26 '19 at 13:59

-3

Sharp cant do this yet.

Alternative method is use canvas to change image opacity before composite. https://github.com/Automattic/node-canvas/blob/master/examples/globalAlpha.js

answered Jul 26 '19 at 13:59

Guilherme Monteiro de Oliveira

177
1
2
9

Watermark with sharp

2 Answers2