2 channel grey+alpha, resize with non-opaque background: vector must have 1 or 3 elements

[banli17]

I used gm to convert the shadowed text into a picture, and then resize the picture with sharp resize, and it reported an error.

nodejs.unhandledRejectionError: linear: vector must have 1 or 3 elements

I tried to modify the color of the shadow and found that sometimes an error is reported, such as when the shadow is #000000. When I change to #040303, no error will be reported.

When I removed the background of sharp resize, I found that no error was reported. But I need transparent text images. Here is the code:

// buf is the png buffer generated by gm
const input = await sharp(buf);
this.imageBuffer = await input.resize({
             width: options.width,
             height: options.height,
             // kernel: sharp.kernel.nearest,
             fit: options.fit ||'contain',
             position: this.sharpPosition,
             background: {r: 0, g: 0, b: 0, alpha: 0 },
           })
             .png()
             .toBuffer();

[lovell]

Please can you provide a sample input image and standalone code (e.g. no undefined variables) to allow someone else to reproduce this problem.

[banli17]

@lovell

This is the picture I generated with gm, I don’t know why I get an error when I use sharp。

When I remove the resize background, it doesn’t report an error

sharp('./axxx.png')
    .resize({
        width: 120,
        height: 30,
        // kernel: sharp.kernel.nearest,
        fit: 'contain',
        background: {r: 0, g: 0, b: 0, alpha: 0},
    })
.png().toBuffer()

[lovell]

I cannot reproduce this on Linux using the latest sharp v0.27.1 with the input image and sample code provided.

I downloaded the sample axxx.png image as follows:

$ curl -so axxx.png https://user-images.githubusercontent.com/12556069/108620148-020f2d00-7465-11eb-8ca6-70fce9b41757.png

It might be that GitHub is altering the image. Please can you provide a standalone repo with a package.json, sample input and code that allows someone else to reproduce this.

[banli17]

year ，it seems github is altering the image, you can try https://github.com/banli17/sharp_test

and i use globally-installed libvips v8.10.0

When the color of fill stoke is .fill('#000000') .stroke('#333333'), an error will be reported, and sometimes no error will be reported, such as fill('red')

[lovell]

Thank you, I can now reproduce this. The input image is 16-bit, 2 channel (grey+alpha) and it fails when the background has a non-opaque alpha channel. I'll investigate further, thanks for reporting this.

[lovell]

This problem relates to sharp's alpha detection, which doesn't currently support 16-bit, 2 channel input. Luckily libvips now provides/exposes a much better has_alpha feature so commit cc37b59 switches to use that instead.

[lovell]

v0.27.2 now available with the fix.