Image Resize and Crop

[Vivi]

How do you advice to resize and crop JPEG and PNG or probably WebP images without rely on 3rd parties dependencies?

It was hard to find a good snippet or could be useful to have basic API function in Go standard library since it's a common feature.

[Michael Jones]

I have an extremely elaborate resizing library, but it is so complex it would not make sense as a standard tool for common uses. (Many convolution kernels, separate windows, forward and backward mapping, separable convolutions, upsampling first for Nyquist issues, strategy phase and then concurrent filtering, etc. good work but over the top) 

If nothing else, you could port Paul Heckbert’s filter program from days of yore. Check graphics gems. 

On Sun, May 10, 2020 at 9:36 AM Vivi <create...@gmail.com> wrote:

How do you advice to resize and crop JPEG and PNG or probably WebP images without rely on 3rd parties dependencies?

It was hard to find a good snippet or could be useful to have basic API function in Go standard library since it's a common feature.

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[robert engels]

All of the code to do scaling and cropping in the ‘image’ package in the stdlib. You ‘draw’ into a new image to do scaling. You use SubImage() to perform cropping. See https://blog.golang.org/image-draw

Alternatively, if you need more advanced scaling operations it would be fairly trivial to port the GIMP scaling operations to Go.

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[Nigel Tao]

On Mon, May 11, 2020 at 4:28 AM robert engels <ren...@ix.netcom.com> wrote:
> All of the code to do scaling and cropping in the ‘image’ package in the stdlib.

Cropping is in the stdlib but scaling is not. Various scaling
algorithms (e.g. nearest neighbor, Catmull-Rom) are in the
golang.org/x/image/draw package instead. As
https://godoc.org/golang.org/x/image/draw says, "This package is a
superset of and a drop-in replacement for the image/draw package in
the standard library".

https://godoc.org/golang.org/x/image/draw#example-Draw has some example code.

[robert engels]

My bad, I didn’t read the API docs completely. Kind of a strange interface declaration in the stdlib image package - that there is only a single rectangle for Draw() and it is bounded by the two images.

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[Vivi]

How does it compare to vipsthumbnail that utilize low memory usage which I believe it use horizontal threading, does Go's image/draw package consume large memory if the image source is huge?

[robert engels]

I don’t know and I doubt anyone else does off the top of their head, so why don’t you write a test and see?

Image processing is highly image and usage dependent, e.g. acceptable quality vs. speed vs. memory.

Using non-quantifiable terms like “huge” is not testable nor verifiable.

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[Randall O'Reilly]

https://github.com/anthonynsimon/bild has parallel image ops of all sorts and is widely used & well supported.

- Randy

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[Nick]

Quoth Vivi:

I'd encourage you to consider trying to implement simple image
manipulation algorithms yourself, if only for practice. I've found the
interfaces in the image package really nice to work with, and have
learned a lot implementing useful things myself based on them.
There's a very good blog post about the package here:
https://blog.golang.org/image

[Vivi]

I found a snippet, memory usage with PNG vs JPG (more than 2x memory than PNG)

https://gist.github.com/logrusorgru/570d64fd6a051e0441014387b89286ca

Why does JPG consume more memory?

Is it fine to have libvips as a dependency for content management system in the same way as PHP require with Imagick or GD?

[Robert Engels]

I’m sorry but that makes no sense. Do you mean file size is smaller? Depends on jpeg compression options. It can be many times smaller than a png. 

On May 11, 2020, at 10:22 AM, Vivi <create...@gmail.com> wrote:



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[Vivi]

It will make sense when you change PNG to JPG and loop 100x to see the actual memory consumption with grtme -v ...

[Robert Engels]

That means there is a memory leak. Once an image is decoded it takes the same amount of memory based on resolution and bit depth.

> On May 11, 2020, at 11:59 AM, Vivi <create...@gmail.com> wrote:
>
> It will make sense when you change PNG to JPG and loop 100x to see the actual memory consumption with grtme -v ...

>
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[Robert Engels]

That’s assuming the image is displayed. It is easier to keep portions of the image on disk with certain formats (eg tiled).

> On May 11, 2020, at 2:40 PM, Robert Engels <ren...@ix.netcom.com> wrote:
>
> That means there is a memory leak. Once an image is decoded it takes the same amount of memory based on resolution and bit depth.