hugo/content/en/_common/methods/resource/processing-spec.md

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Processing specification

The processing specification is a space-delimited, case-insensitive list containing one or more of the following options in any sequence:

action

Specify one of crop, fill, fit, or resize. This is applicable to the Process method and the images.Process filter. If you specify an action, you must also provide dimensions.

anchor

The focal point used when cropping or filling an image. Valid options include TopLeft, Top, TopRight, Left, Center, Right, BottomLeft, Bottom, BottomRight, or Smart. The Smart option utilizes the muesli/smartcrop package to identify the most interesting area of the image. This defaults to the anchor parameter in your project configuration.

background color

The background color used when converting transparent images to formats that do not support transparency, such as PNG to JPEG. This color also fills the empty space created when rotating an image by a non-orthogonal angle if the space is not transparent and a background color is not specified in the processing specification. The value must be an RGB hexadecimal color. This defaults to the bgColor parameter in your project configuration.

compression

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The encoding strategy used for the image. Options are lossy or lossless. Note that lossless is only supported by the WebP format. This defaults to the compression parameter in your project configuration.

dimensions

The dimensions of the resulting image, in pixels. The format is WIDTHxHEIGHT where WIDTH and HEIGHT are whole numbers. When resizing an image, you may specify only the width (such as 600x) or only the height (such as x400) for proportional scaling. Specifying both width and height when resizing an image may result in non-proportional scaling. When cropping, fitting, or filling, you must provide both width and height such as 600x400.

format

The format of the resulting image. Valid options include bmp, gif, jpeg, png, tiff, or webp. This defaults to the format of the source image.

hint

The encoding preset used when processing WebP images, equivalent to the -preset flag for the cwebp CLI. Valid options include drawing, icon, photo, picture, or text. This defaults to the hint parameter in your project configuration.

Value	Example
drawing	Hand or line drawing with high-contrast details
icon	Small colorful image
photo	Outdoor photograph with natural lighting
picture	Indoor photograph such as a portrait
text	Image that is primarily text

quality

The visual fidelity of the image, applicable to JPEG and WebP formats when using lossy compression. The format is qQUALITY where QUALITY is a whole number between 1 and 100, inclusive. Lower numbers prioritize smaller file size, while higher numbers prioritize visual clarity. This defaults to the quality parameter in your project configuration.

resampling filter

The algorithm used to calculate new pixels when resizing, fitting, or filling an image. Common options include box, lanczos, catmullRom, mitchellNetravali, linear, or nearestNeighbor. This defaults to the resampleFilter parameter in your project configuration.

Filter	Description
box	Simple and fast averaging filter appropriate for downscaling
lanczos	High-quality resampling filter for photographic images yielding sharp results
catmullRom	Sharp cubic filter that is faster than the Lanczos filter while providing similar results
mitchellNetravali	Cubic filter that produces smoother results with less ringing artifacts than CatmullRom
linear	Bilinear resampling filter, produces smooth output, faster than cubic filters
nearestNeighbor	Fastest resampling filter, no antialiasing

Refer to the source documentation for a complete list of available resampling filters. If you wish to improve image quality at the expense of performance, you may wish to experiment with the alternative filters.

rotation

The number of whole degrees to rotate an image counter-clockwise. The format is rDEGREES where DEGREES is a whole number. Hugo performs rotation before any other transformations, so your target dimensions and any anchor should refer to the image orientation after rotation. Use r90, r180, or r270 for orthogonal rotations, or arbitrary angles such as r45. To rotate clockwise, use a negative number such as r-45. To automatically rotate an image based on its Exif orientation tag, use the images.AutoOrient filter instead of manual rotation.

Rotating by non-orthogonal values increases the image extents to fit the rotated corners. For formats supporting alpha channels such as PNG or WebP, this resulting empty space is transparent by default. If the target format does not support transparency such as JPEG, or if you explicitly specify a background color in the processing specification, the space is filled. If a color is required but not specified in the processing string, it defaults to the bgColor parameter in your project configuration.