Get the actual width/height of an image

Get the actual width/height of an image

[Yuan Fu]

Here’s what I want to do: I want to show an image in slices, and I want to be able to resize the image to certain width/height. For example, I want to set the width of an image to, say, 300 pixels. IIUC, to show the image in slices I need to now how many rows to use (row-count = image-height / line-height). However, there is no way for me to know what the height should be to make the width to be 300 pixels. There doesn’t seem to be a function to get the aspect ratio of the image, or the actual pixel height/width of the image. So can I get this information?

Thanks,
Yuan

Re: Get the actual width/height of an image

[Emanuel Berg via Users list for the GNU Emacs text editor]

Yuan Fu wrote:

> There doesn’t seem to be a function to get the
> aspect ratio of the image, or the actual pixel
> height/width of the image. So can I get
> this information?

For everything batch and graphics, use ImageMagick.

For the specific problem, you can use the command
identify(1) which is part of ImageMagick.

  $ identify zhanna-friske.png 
  zhanna-friske.png PNG 1280x720 1280x720+0+0 8-bit sRGB 835952B 0.000u 0:00.000

You can then parse the output to answer an even more
specific question, e.g. what the height is:

  #! /bin/zsh
  pic-height () {
      local img=$1
      identify $img | awk '{print $3}' | cut -d 'x' -f 2
  }

  $ pic-height zhanna-friske.png 
  720

https://dataswamp.org/~incal/conf/.zsh/gfx

-- 
underground experts united
http://user.it.uu.se/~embe8573
https://dataswamp.org/~incal

Re: Get the actual width/height of an image

[Corwin Brust]

Greetings!

On Mon, Sep 14, 2020 at 3:53 PM Emanuel Berg via Users list for the
GNU Emacs text editor <help-gnu-emacs@gnu.org> wrote:
>
> Yuan Fu wrote:
>
> > There doesn’t seem to be a function to get the
> > aspect ratio of the image, or the actual pixel
> > height/width of the image. So can I get
> > this information?


I think we can get the dimensions from `image-size', but note the
PIXELS argument:

(image-size SPEC &optional PIXELS FRAME)

  | Documentation
  | Return the size of image SPEC as pair (WIDTH . HEIGHT).

  | PIXELS non-nil means return the size in pixels, otherwise return the
  | size in canonical character units.

  | FRAME is the frame on which the image will be displayed.  FRAME nil
  | or omitted means use the selected frame.

  | Calling this function will result in the image being stored in the
  | image cache.  If this is not desirable, call image-flush after
  | calling this function.


> For everything batch and graphics, use ImageMagick.

I think Emacs is moving away from ImageMagick and toward
"self-implemented" image manipulation &ct. functions.   Not that IM
has "gotten rusty" -- it isn't preferred from an elisp perspective
which could be important in terms of portability to other Emacsen.

>
> --
> underground experts united
> http://user.it.uu.se/~embe8573
> https://dataswamp.org/~incal
>
>

Regards,
Corwin

Re: Get the actual width/height of an image

[Yuan Fu]

> On Sep 14, 2020, at 5:18 PM, Corwin Brust <corwin@bru.st> wrote:
> 
> Greetings!
> 
> On Mon, Sep 14, 2020 at 3:53 PM Emanuel Berg via Users list for the
> GNU Emacs text editor <help-gnu-emacs@gnu.org> wrote:
>> 
>> Yuan Fu wrote:
>> 
>>> There doesn’t seem to be a function to get the
>>> aspect ratio of the image, or the actual pixel
>>> height/width of the image. So can I get
>>> this information?
> 
> 
> I think we can get the dimensions from `image-size', but note the
> PIXELS argument:
> 
> (image-size SPEC &optional PIXELS FRAME)
> 
>  | Documentation
>  | Return the size of image SPEC as pair (WIDTH . HEIGHT).
> 
>  | PIXELS non-nil means return the size in pixels, otherwise return the
>  | size in canonical character units.
> 
>  | FRAME is the frame on which the image will be displayed.  FRAME nil
>  | or omitted means use the selected frame.
> 
>  | Calling this function will result in the image being stored in the
>  | image cache.  If this is not desirable, call image-flush after
>  | calling this function.
> 
> 

Wow, exactly what I want! Wonder why I missed it when reading Info. Thanks!

Yuan

Re: Get the actual width/height of an image

[Stefan Monnier]

> I think Emacs is moving away from ImageMagick and toward
> "self-implemented" image manipulation &ct. functions.   Not that IM
> has "gotten rusty" -- it isn't preferred from an elisp perspective
> which could be important in terms of portability to other Emacsen.

Actually, yes, part of the reason is that it has gotten rusty, IIRC.


        Stefan

Re: Get the actual width/height of an image

[Emanuel Berg via Users list for the GNU Emacs text editor]

Stefan Monnier wrote:

>> I think Emacs is moving away from ImageMagick and
>> toward "self-implemented" image manipulation &ct.
>> functions. Not that IM has "gotten rusty" -- it
>> isn't preferred from an elisp perspective which
>> could be important in terms of portability to
>> other Emacsen.
>
> Actually, yes, part of the reason is that it has
> gotten rusty, IIRC.

Well, if that is the reason perhaps efforts should be
made to remove the rust (actually, things that you
use typically don't rust) rather than have every
software project's team of developers implementing
their own way of getting the dimensions of an
image? ;)

-- 
underground experts united
http://user.it.uu.se/~embe8573
https://dataswamp.org/~incal

Re: Get the actual width/height of an image

[Stefan Monnier]

> Well, if that is the reason perhaps efforts should be
> made to remove the rust (actually, things that you

Usually rust accumulates there where nobody wants to touch the code.


        Stefan