Publ: Image renditions

Last updated: 2018-04-05 2:12 AM (6 years ago)

Image rendition support

In entries

See the entry format article

In templates

Pass these in as parameters to entry.body and/or entry.more to configure the default values for entry images.

The template also gets a function, image(), that allows the template itself to render images.

Configuration values

General configuration

absolute: Whether to produce absolute URLs
link: Put a hyperlink on the image pointing to the given URL. Acceptable values:
- Any string: Treated like an ordinary Markdown link (including linking to local entries and files)
- False: Prevent any link from being added, including for a gallery
- True: Link directly to the fullsize rendition of the image, overriding gallery display
link_class: What CSS class to apply to the image’s hyperlink
image_loading: What image loading mode to use. Possible values:
- "lazy": Instruct the browser to only load the images when they come into view on the page (default)
- "eager": Instruct the browser to load the image as soon as possible
- False: Use the browser default (usually "eager")

Style options

img_class: If set, sets the class attribute on the image tag
img_style, style: A string or a list of strings, which provide inline CSS rules to the <img> element
When the element is written, any attributes in style will override those in img_style; the intention is that in a Markdown tag, img_style comes from the container and style comes from the image.
shape: Adds the CSS3 shape-outside attribute to the image tag’s style; can be one of the following:
- True: Uses the base rendition of the image itself (this is usually what you want)
- A string value: uses the specified image’s alpha channel as the shape
  This can be any path scheme supported by the image path scheme (e.g. local-file.png, /common/absolute-file.png, @images/static-file.png, //example.com/remote-file.png).
For example, if you have an image inset-image.jpg that you want to mask off with inset-image-mask.png and float left, you can do:
```
![](inset-image.jpg{shape="inset-mask.png",style="float:left"})
```
It is better to make image insets' float rules part of your stylesheet, however, so that it can be responsive; for example:
```
![](inset-image.jpg{shape="inset-mask.png",img_class="inset-left"})
```
The size of the outline image will be mapped the same as the base image, wherever possible; for example:
```
![{320,320}](inset-image.jpg{shape="inset-mask.png"})
```
will size both the image and its mask to fit within a 320x320 square.

Inline image sizing

scale: What factor to scale the source image down by (e.g. 3 = the display size should be 33%)
scale_min_width: The minimum width to target based on scaling
scale_min_height: The minimum height to target based on scaling
width: The width to target
height: The height to target
max_width: If present and smaller than width, use this instead (useful for templates)
max_height: If present and smaller than height, use this instead (useful for templates)
resize: If both width and height are specified, how to fit the image into the rectangle if the aspect ratio doesn’t match
- fit: Fit the image into the space (default)
- fill: Fill the space with the image, cropping off the sides
- stretch: Distort the image to fit
scale_filter: What scaling algorithm to use when resampling the image. Case-insensitive. See the Pillow documentation for more information on the available algorithms. Defaults to lanczos.
crop: Crops the thumbnail to the given rectangle, which is provided in the form of (x,y,w,h) or 'x,y,w,h', where x and y are the coordinates of the top-left corner and w and h are the size of the rectangle.
The () notation is more flexible, but sometimes it doesn’t work; in that case, use the '' notation instead.
fill_crop_x: If resize="fill", where to take the cropping (0=left, 1=right); default=0.5
fill_crop_y: If resize="fill", where to take the cropping (0=top, 1=bottom); default=0.5

Note: Images will never be scaled to larger than their native resolution. (In the future there may be an option to still resize it larger client-side, where the actual rendition will be the native size but the <img> tag gets the expanded width and height.)

File format options

format: Select the format to display the image as (defaults to the original format)
background: The background color to use when converting transparent images (such as PNG or WebP) to non-transparent formats (such as JPEG); this can also be used to force an image to be non-transparent.
This parameter can be in a number of formats:
- A named color such as "black" or "white"
- An HTML-style hex code such as "#ff7733" or "#f73"
- An RGB tuple such as (0,127,35) (note the lack of quotes!)
If you’re daring you can also use any of the other color formats supported by PIL.ImageColor, e.g. "hsl(0,100%,50%)"
quality: The quality level to use for all renditions, if applicable
quality_ldpi: The quality level to use for low-DPI renditions
quality_hdpi: The quality level to use for high-DPI renditions
lossless: Whether to use lossless compression, if available
quantize: How many colors to use in the output color palette, if available

Image set options

These options drive the behavior of image sets.

figure: Whether to wrap the image set inside a <figure>. If this is set to a string, the string is used as a CSS class.
caption: Adds a caption to the image set. Markdown is supported. Implies figure=True.
div_class: The CSS class to use for the containing <div>
div_style: A string or a list of strings, which provide inline CSS rules to the <div> element
gallery_id: An identifier for the Lightbox image set (for use with lightbox.js or any other lightbox implementation that uses the data-lightbox property to function)
- Note: If link is set (including to False), this option has no effect
count: How many images to allow in the image set (useful for feeds)
count_offset: If count is set, also skip this number of images at the beginning
fullsize_width: The maximum width for the popup image
fullsize_height: The maximum height for the popup image
fullsize_crop: The cropping rectangle for the full-sized image; see crop for the format.
fullsize_quality: The JPEG quality level to use for the popup image
fullsize_format: What format the popup image should be in (defaults to the original format)
fullsize_background: The background color to use when converting transparent images (such as .png) to non-transparent formats (such as .jpg)
more_text: If images were skipped due to count or count_offset, add this text after the image set. This string will be rendered with the following template arguments:
- {count}: The total number of images in the image set
- {remain}: The number of images not shown
more_link: If more_text is shown, it will be wrapped in a link with this location
more_class: If more_text is shown, it will be given this CSS class (either on the <a> tag if it’s a link, or via a <span>)

Template meta-options

prefix: Specify one or more prefixes to check for additional rendition options.
For example, if you have the following in your index.html:
```
{{ entry.body(prefix='index_') }}
```
then if you have an image like this:
```
![](me.jpg{crop='5,5,500,400',index_crop='20,20,400,300'})
```
then on the page rendered via index.html it will be equivalent to:
```
![](me.jpg{crop='20,20,400,300'})
```
You can also specify multiple prefixes to check by putting them in a list, e.g.
```
{{ entry.body(prefix=['index_','blog_']) }}
```
In the case of multiple prefixes, the last one takes priority, so list them as least to most specific.
This is probably only useful from a template file, rather than from an entry. Using a prefix on the prefix attribute itself (e.g. ![{index_prefix='foo_'}](me.jpg{foo_format='png'})) is undefined behavior and should probably make your head hurt to think about, and no it isn’t Turing-complete so don’t bother trying.

Useful template examples

A webcomic

index.html and entry.html:

This will treat source images as being 3x screen resolution, make images scale to no narrower than 480 pixels and to no wider than 960 pixels, encourage them to be a JPEG (with transparency turning white), and with 35% JPEG quality for the high-DPI rendition.

{{ entry.body(
    scale=3,
    scale_min_width=480
    width=960,
    format="jpg",
    background="white",
    quality_hdpi=35)
}}

feed.xml:

This will resize the image to no more than 400 pixels wide or tall and crop the thumbnail to the top or left of the image (making for a useful non-punchline-destroying excerpt).

{{ entry.body(link=entry.link(
    absolute=True,
    max_width=400,
    max_height=400,
    resize="fill",
    fill_crop_x=0,
    fill_crop_y=0)
}}

In the above example, if you have a comic that is provided at screen resolution to begin with (such as guest art) you can override the default scaling with e.g.:

![](guest-comic.png{scale=1} "Amazing guest comic!")

Or if there’s one you want to force to a specific size:

![](special-comic.jpg{width=960,height=480})

which can also be written more compactly as:

![](special-comic.jpg{960,480})

A photo gallery

With the below setup, if an entry provides an image set with a count_offset parameter, e.g.

![{count_offset=2}](image1.jpg | image2.jpg | image3.jpg | image4.jpg)

then on the index and feed (where there’s a count set) skip the first two images and thus show image3.jpg as the first image. This allows you to set a “poster” frame for the image set as a whole.

`index.html`

This will show just the first image in the gallery at its original aspect, and then link the user to the full gallery page with an image count.

{{ entry.body(
    width=640,
    height=640,
    link=entry.link,
    count=1,
    more_text='Show {count} images',
    more_link=entry.link)
    }}

`entry.html`

This will show the full gallery with square thumbnails and a reasonable default gallery ID, and the full images at 4K resolution. The thumbnails will be wrapped in a <div class="gallery_thumbs">.

{{ entry.body(
    width=640,
    height=640,
    resize="fill",
    gallery_id=entry.uuid,
    div_class="gallery_thumbs",
    fullsize_width=3840,
    fullsize_height=2160)
}}

`feed.xml`

This will show tiny thumbnails of the first three images of the gallery and will link to the full gallery page.

{{ entry.body(
    max_width=300,
    max_height=300,
    count=3,
    link=entry.link,
    more_text='{remain} more images in gallery')
}}