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Thumbnail width for portrait images #71

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boris612 opened this issue Apr 1, 2020 · 3 comments · May be fixed by libvips/libvips#1639
Open

Thumbnail width for portrait images #71

boris612 opened this issue Apr 1, 2020 · 3 comments · May be fixed by libvips/libvips#1639
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@boris612
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boris612 commented Apr 1, 2020

ThumbnailImage method allows a user to specify only width, but it does not work correctly for portrait images (or it is not correctly documented)
For example, if you write the following code

var image = Image.NewFromFile(filename);
Image thumbnail = image.ThumbnailImage(300);

for the image with dimensions 600x900 then it would produce 200x300 thumbnail instead of 300x450.
It appears that it translates to vipsthumbnail.exe -s 300 instead to vipsthumbnail.exe -s 300x

A workaround is to calculate height or to give some large value for height
Image thumbnail = image.ThumbnailImage(300, height: a big enough number)
@kleisauke kleisauke added the question Further information is requested label Apr 6, 2020
@kleisauke
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kleisauke commented Apr 6, 2020 •
edited

This is a known issue in libvips. See libvips/libvips#709 for a future possible enhancement.

A workaround is to calculate height or to give some large value for height
Image thumbnail = image.ThumbnailImage(300, height: a big enough number)

Indeed, you can set the target resize height to VIPS_MAX_COORD (which is currently 10000000) to prevent reduction or enlargement in the vertical axis and vice versa for the target resize width (that's what vipsthumbnail does).

var image = Image.NewFromFile(filename);
Image thumbnail = image.ThumbnailImage(300);

You could use Image.Thumbnail instead. Because the image has already been opened, it can't do any of the shrink tricks that makes thumbnailing fast. #64 might be relevant here.

@boris612
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boris612 commented Apr 6, 2020

Thanks for the info, it solves the problem. Just a suggestion. Maybe you could write a similar note in the method summary, and/or define public constant VIPS_MAX_COORD and set default height value to it instead to null.

kleisauke added a commit to kleisauke/libvips that referenced this issue May 3, 2020
@kleisauke
Default height to VIPS_MAX_COORD for vips_thumbnail
2f57ea8 
This is to prevent reduction in the vertical axis when the height is omitted.

See: kleisauke/net-vips#71.
kleisauke added a commit to kleisauke/libvips that referenced this issue May 3, 2020
@kleisauke
Default height to VIPS_MAX_COORD for vips_thumbnail
755ecee 
This to prevent reduction in the vertical axis when the height is omitted.

See: kleisauke/net-vips#71.
@kleisauke kleisauke linked a pull request May 3, 2020 that will close this issue
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@kleisauke
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See libvips/libvips#1639 for a draft that changes the vips_thumbnail into a resize based on a specific axis. Any feedback is welcome!

@kleisauke kleisauke mentioned this issue Sep 14, 2020
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Default height to VIPS_MAX_COORD for vips_thumbnail kleisauke/libvips
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@boris612 @kleisauke