description for "crop" directive in ngx_http_image_filter_module's document is not correct

[chen cw]

We are going to translate this passage into Chinese according to your
explanation.

Thank you


On Mon, Oct 29, 2012 at 11:22 PM, Homutov Vladimir <vl at nginx.com> wrote:

> On Mon, Oct 29, 2012 at 12:28:47PM +0400, Homutov Vladimir wrote:
> > On Mon, Oct 29, 2012 at 11:47:02AM +0800, chen cw wrote:
> > > Hi,
> > >     we think the description for  "crop" directive in
> > > ngx_http_image_filter_module's document is not correct, or at least not
> > > clear. It says "proportionally reduces an image to the size of the
> largest
> > > side". we have tested and now believes it should be  not "the largest
> > > side", but "the smallest side".
> > >
> >
> > Hi!
> >
> > The 'largest side' is related to the arguments of the 'crop'
> > directive, not the source image size.
> >
> > With this in mind, the description is correct.
> >
> > For example,
> >
> > command 'crop 600x50' for source image 640x480 will:
> >
> > 1) proportionally reduce largest (600 - horizontal) side: 640->600
> > 2) crops extraneous edges by another side - vertical: 480->50
> >
> > the result is that image got reduced horizontally a bit (proportionally)
> > and cropped by vertical side (50 center pixels left).
> >
> > command 'crop 600x50' for 480x640 image will give 480x50:
> >
> > 1) proportionally reduce horizontal side (no actions, 480 < 600
> > requested)
> > 2) leave 50 center pixels on another side
> >
> > command 'crop 50x600' for 640x480 image will give 50x480:
> >
> > 1) largest side is 600 (vertical), no actions (requested 600 < 480
> > actual)
> > 2) another side is cropped to 50 pixels.
>
> actually, things are a bit more complicated:
>
> what is important, it is the correlation between width/height ratio
> of the source image and the desired size.
>
> The 'largest side' phrase is misleading, as ratios are
> compared, not sizes; thus largest ratio is important, not side.
>
> The effect is that crop chooses dimension (width or height) to be
> resized to reach the best fit of source image in the destination frame.
>
> if the source image has w/h ratio less than requested frame, it will be
> proportionally resized up to new width and extra height will be cut.
>
> if the source image has w/h ratio greater than or equal to requested
> frame, it
> will be proportionally resized to the new height and extra width will be
> cut.
>
> Example:
>
> #    source image:640x480    (w/h = 1.333)
> image_filter crop 320 250; # (w/h = 1.28)
>
> since 1.33 > 1.28, source image is resized up to desired height
> first (333x250) and then extra width cut (320x250).
>
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>



-- 

--

Charles Chen

Software Engineer

Server Platforms Team at Taobao.com
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