From DynamicImage to Vec<u8>

[nricciardi]

I would use this image library to perform some elaboration over images. In particular, I would open an image, compress and save as base64. I would save it as base64 to include that in html page.
At the moment, I'm reading image using File:

let mut image = File::open(image_path.clone()).unwrap();

let mut buffer: Vec<u8> = Vec::new();
image.read_to_end(&mut buffer).unwrap();

and then I use base64 library.

Now, I would use image::load_from_memory or image::open to obtain DynamicImage and then get the Vec from it.

I have tried with as_flat_samples_u8().unwrap().samples and into_bytes(), but the Vec of image.read_to_end(&mut buffer) is different from the Vec of into_bytes(). This last is longer.

How can I fix?

[fintelia]

You are probably looking for the write_to method:

let mut bytes: Vec<u8> = Vec::new();
img2.write_to(&mut Cursor::new(&mut bytes), image::ImageOutputFormat::Png)?;

If you call into_bytes, you get the raw pixel values of the image. While write_to encodes the image to a specific format (in this case PNG).

[fintelia]

The write_to method doesn't dump it to a file. It just encodes the data into an image file format. That's a necessary step because web browsers expect the base64 string to be encoded in some such format.

If you want to switch to WebP or AVIF then you can change the image::ImageOutputFormat part of the sample accordingly. Though you might have to enable an additional crate feature

[nricciardi]

Yes, but it store "new image" in a Vec. I would replace my DynamicImage variable.

[fintelia]

I'm not sure what you're asking. If you want to get the backing Vec out of a DynamicImage then you can match on its variants and call into_raw on them. But it'll contain the raw pixel values rather than having them encoded in some image format.

Conversely, if you want the original bytes from the file, there's nothing wrong with your File::open/read_to_end approach.

[nricciardi]

I would open an image file and save it in a DynamicImage variable, then compress in WebP or AVIF to reduce base64 string length. So, I would override store new encoded image in DynamicImage type. Some like this:

let image: DynamicImage = image::load_from_memory(vec_u8_buffer);

image = image.into_avif();
// or .into_webp()

[fintelia]

A DynamicImage holds raw uncompressed pixel data. You cannot put AVIF or WebP data into it.