Convert image data from Vec<u8> to Image<&[u8]> for turbojpeg

help
1

I'm rather new to Rust and playing around with resizing images using turbojpeg, since it's rather quick.

This is basically what I'm doing:

    //read jpeg from disc
    let jpeg_data = std::fs::read(img_path_in).unwrap();
    //decompress jpeg image data as Image<Vec<u8>>
    let img = turbojpeg::decompress(&jpeg_data,turbojpeg::PixelFormat::RGB).unwrap();
    //convert image data to be able to resize image
    let img_to_resize = img.as_deref().pixels;
    ...resize image....
    //compress the image data as jpeg
    let jpeg_data_out = turbojpeg::compress(img_resized, 75, turbojpeg::Subsamp::Sub2x2).unwrap();
    //save jpeg to file
    std::fs::write(img_path_out, jpeg_data_out).unwrap();

I have been using the resize create to try and resize the image data, which seem to work, but how do I go about converting the resized image data, which is of type Vec<u8>, to Image<&[u8]> that turbojpeg::compress() accepts?

I might be doing something fundamentally wrong here, and therefor asking the wrong question so feel free to contribute to solving the problem instead of answering my question.

2

You can construct an Image directly. Most of the fields should be fairly obvious, but you may have to experiment a bit to get pitch right.

3

I haven't used these libraries, but I would look at image::ImageBuffer::from_raw(), it says it can take a Vec as the input.

4

Yes, I was just trying that but still some problems with wrong type:

let img_resized = turbojpeg::Image {
   pixels: dst,
   width: 320, 
   pitch: 320 * turbojpeg::PixelFormat::RGB.size() * 2,
   height: 240,
   format: turbojpeg::PixelFormat::RGB
  };

But then I get expected struct Image<&[u8]>, found struct Image<Vec<u8>>
How do I go from my <&Vec<u8>> to <&[u8]>?

5

dst.as_slice() should work

6

That worked but now I get:

error[E0658]: use of unstable library feature 'slice_pattern': stopgap trait for slice patterns
use core::slice::SlicePattern;
7

You may have accidentally imported the unstable SlicePattern trait as a code completion for as_slice. Just delete the import of the trait, there's an inherent as_slice method on Vec and that's the one you want.

1 Like
8

Ha, that was funny. It would have taken me a while to figure that one out.
After removing use core::slice::SlicePattern; it works, thank you.
(It doesn't really work but it compiles so I can fix the rest)

9

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