hugo/docs/content/en/content-management/image-processing/index.md at 4b286b9d2722909d0682e50eeecdfe16c1f47fd8

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Bjørn Erik Pedersen 4b286b9d27 resources/images: Allow to set background fill colour

Closes #6298

2019-10-20 22:06:58 +02:00

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The Image Page Resource

The image is a [Page Resource]({{< relref "/content-management/page-resources" >}}), and the processing methods listed below does not work on images inside your /static folder.

To get all images in a [Page Bundle]({{< relref "/content-management/organization#page-bundles" >}}):

{{ with .Resources.ByType "image" }}
{{ end }}

Image Processing Methods

The image resource implements the methods Resize, Fit and Fill, each returning the transformed image using the specified dimensions and processing options.

Resize: Resizes the image to the specified width and height.

// Resize to a width of 600px and preserve ratio
{{ $image := $resource.Resize "600x" }} 

// Resize to a height of 400px and preserve ratio
{{ $image := $resource.Resize "x400" }} 

// Resize to a width 600px and a height of 400px
{{ $image := $resource.Resize "600x400" }}

Fit: Scale down the image to fit the given dimensions while maintaining aspect ratio. Both height and width are required.

{{ $image := $resource.Fit "600x400" }}

Fill: Resize and crop the image to match the given dimensions. Both height and width are required.

{{ $image := $resource.Fill "600x400" }}

{{% note %}} Image operations in Hugo currently do not preserve EXIF data as this is not supported by Go's image package. This will be improved on in the future. {{% /note %}}

Image Processing Options

In addition to the dimensions (e.g. 600x400), Hugo supports a set of additional image options.

Background Color

The background color to fill into the transparency layer. This is mostly useful when converting to a format that does not support transparency, e.g. JPEG.

You can set the background color to use with a 3 or 6 digit hex code starting with #.

{{ $image.Resize "600x jpg #b31280" }}

For color codes, see https://www.google.com/search?q=color+picker

JPEG Quality

Only relevant for JPEG images, values 1 to 100 inclusive, higher is better. Default is 75.

{{ $image.Resize "600x q50" }}

Rotate

Rotates an image by the given angle counter-clockwise. The rotation will be performed first to get the dimensions correct. The main use of this is to be able to manually correct for EXIF orientation of JPEG images.

{{ $image.Resize "600x r90" }}

Anchor

Only relevant for the Fill method. This is useful for thumbnail generation where the main motive is located in, say, the left corner. Valid are Center, TopLeft, Top, TopRight, Left, Right, BottomLeft, Bottom, BottomRight.

{{ $image.Fill "300x200 BottomLeft" }}

Resample Filter

Filter used in resizing. Default is Box, a simple and fast resampling filter appropriate for downscaling.

Examples are: Box, NearestNeighbor, Linear, Gaussian.

See https://github.com/disintegration/imaging for more. If you want to trade quality for faster processing, this may be a option to test.

{{ $image.Resize "600x400 Gaussian" }}

Target Format

By default the images is encoded in the source format, but you can set the target format as an option.

Valid values are jpg, png, tif, bmp, and gif.

{{ $image.Resize "600x jpg" }}

Image Processing Examples

The photo of the sunset used in the examples below is Copyright Bjørn Erik Pedersen (Creative Commons Attribution-Share Alike 4.0 International license)

This is the shortcode used in the examples above:

{{< code file="layouts/shortcodes/imgproc.html" >}} {{< readfile file="layouts/shortcodes/imgproc.html" >}}
{{< /code >}}

And it is used like this:

{{</* imgproc sunset Resize "300x" /*/>}}

{{% note %}} Tip: Note the self-closing shortcode syntax above. The imgproc shortcode can be called both with and without inner content. {{% /note %}}

Image Processing Config

You can configure an imaging section in config.toml with default image processing options:

[imaging]
# Default resample filter used for resizing. Default is Box,
# a simple and fast averaging filter appropriate for downscaling.
# See https://github.com/disintegration/imaging
resampleFilter = "box"

# Default JPEG quality setting. Default is 75.
quality = 75

# Anchor used when cropping pictures.
# Default is "smart" which does Smart Cropping, using https://github.com/muesli/smartcrop
# Smart Cropping is content aware and tries to find the best crop for each image.
# Valid values are Smart, Center, TopLeft, Top, TopRight, Left, Right, BottomLeft, Bottom, BottomRight
anchor = "smart"

# Default background color. 
# Hugo will preserve transparency for target formats that supports it,
# but will fall back to this color for JPEG.
# Expects a standard HEX color string with 3 or 6 digits.
# See https://www.google.com/search?q=color+picker
bgColor = "#ffffff"

All of the above settings can also be set per image procecssing.

Smart Cropping of Images

By default, Hugo will use the Smartcrop, a library created by muesli, when cropping images with .Fill. You can set the anchor point manually, but in most cases the smart option will make a good choice. And we will work with the library author to improve this in the future.

An example using the sunset image from above:

Image Processing Performance Consideration

Processed images are stored below <project-dir>/resources (can be set with resourceDir config setting). This folder is deliberately placed in the project, as it is recommended to check these into source control as part of the project. These images are not "Hugo fast" to generate, but once generated they can be reused.

If you change your image settings (e.g. size), remove or rename images etc., you will end up with unused images taking up space and cluttering your project.

To clean up, run:

hugo --gc

{{% note %}} GC is short for Garbage Collection. {{% /note %}}

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