pixeli

v1.0.5

Published

a month ago

A lightweight command-line tool for merging multiple images into customizable grid layouts.

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pakdad-mousavi

cli nodejs npm image-processing image-merge

Pixeli (Pre-release)

Pixeli is a typescript-first, lightweight, and flexible command-line tool and library for merging multiple images into clean, customizable grid layouts. It’s designed for speed and simplicity, making it ideal for generating collages, previews, gallery layouts, inspiration boards, and composite images without relying on heavy desktop software.

Pixeli uses Sharp, a Node.js wrapper for the libvips library which is based on C. This makes it an extremely fast tool with support for PNG, JPG, GIF, SVG, AVIF, etc.

The tool currently supports four main layout modes: Grid, Masonry (horizontal / vertical), Template, and Collage. Each of them provide a distinct visual style to match a project's needs, for example:

| Grid (1:1 images) | Contact Sheet Grid | |---|---| | | | | Masonry (Horizontal) | Masonry (Vertical) | | | | | Template (Instagram Grid) | Template (Vertical Book Spread) | | | | | Template (Horizontal Book Spread) | Template (Dashboard Shot) | | | | | Template (Art Gallery) | Collage | | | |

Installation

Pixeli can be installed using npm. Simply run the following command to install it globally on your machine:

npm i -g pixeli

If you're interested in the library functions and not the CLI, you can add it to your project instead of a global install:

npm i pixeli

You can also run pixeli directly with npx without installing it globally. This is convenient for quick experiments or one-off usage:

npx pixeli merge <subcommand> [options] <files...>

Quick CLI Examples

To run these examples, you can visit the GitHub Repository and use the images in the Samples directory, if you don't already have your own set of images.

All merge commands are under pixeli and can be used like so: pixeli [merge-mode] [options]

Basic Grid

To create a basic grid with 1:1 images, you can use the grid merge command. You'll also need to provide the individual filepaths to use, or use the -rd (--recursive and --directory) flags to get all the images from the specified directory:

pixeli grid -rd ./samples/images

Without the -r flag, only the images in the directory will be scanned, and any sub-directories will be ignored.

Grid with Rectangular Images

To create a grid with images that all have the same aspect ratio, you can specify the aspect ratio to use for all images using the --ar flag:

pixeli grid -rd ./samples/images --ar 16:9

Grid with 8 Columns

You can also customize the number of columns that you'd like the final image to have using the -c flag, followed by the number of columns:

pixeli grid -rd ./samples/images -c 8

Contact Sheet

Contact sheet style grids can also be made using pixeli. To include each file name under its respective image, the --ca flag can be used:

pixeli grid -rd ./samples/images --ca

The caption color can also be specified using the --cc flag, followed by a hex color:

pixeli grid -rd ./samples/images --ca --cc "#ff0000"

Masonry Layout

To create a masonry style image, you can use the masonry merge command. The -rd flag is used to specify which directory to use, and the canvas width can be specified using the --cvw flag:

pixeli masonry -rd ./samples/images --cvw 4000

By default, the masonry merge command uses a horizontal flow, but a vertical one can be specified using the -f flag, followed by the --cvh to specify the canvas height:

pixeli merge masonry -rd ./samples/images -f vertical --cvh 4000

Note that the masonry command always requires either the --cvw or --cvh option, depending on the flow.

Template Layout

Template layouts require a JSON template which describe your specific layout. The -t flag is used to specify the path to a JSON template:

pixeli template -rd ./samples/images -t ./template.json

You could also use one of the presets provided using the -p flag:

pixeli template -rd ./samples/images -p instagram-grid

To learn about the JSON template, see JSON Templates.

Collage Layout

Collage layouts are similar to grid layouts, in a way. Images are arranged in a grid, jittered, rotated, and overlapped to create a photo-wall style grid:

pixeli collage -rd ./samples/images

To customize the image sizes, use the -w flag:

pixeli collage -rd ./samples/images -w 400

To change the overlap percentage of any two images in the collage, use the --op flag:

pixeli collage -rd ./samples/images --op 10

For varying image sizes, you can use the --wv flag to change the image width variance (in pixels):

pixeli collage -rd ./samples/images --wv 50

To change the minimum and maximum degrees to rotate each image by, use the --rr flag to customize the rotation range:

pixeli collage -rd ./samples/images --rr 15

Full CLI Documentation

pixeli

Usage: pixeli <subcommand> [options] <input...> -o <output>

The pixeli command is what allows you to create grids and mosaics with your images. | Subcommand | Description | Options | | ---------- | ------------------------------------------------------------------------------------------------------------------------------------------------- | ---------------------------------------------------------------- | | grid | Merge images into a uniform rows × columns grid, optionally with captions and per-image aspect ratios. | See grid options table | | masonry | Merge images into a dynamic masonry layout, preserving natural image proportions. Supports vertical or horizontal flow and alignment options. | See masonry options table | | template | Merge images into a pre-defined layout, based on the template provided, or the preset used. | See template options table | | collage | Merge images into a messy, photo-wall style grid, great for posters or aesthetic layouts. | See collage options table |

The following options and flags are shared for all of the subcommands under the pixeli command: | Option | Default | Description | | ------------------------------ | -------------- | ---------------------------------------------------------------------------------------------------------------------------------- | | [files...] | — | Image file paths to merge. You can specify multiple files or if you prefer directories, use --dir. | | -d, --dir <path> | — | Path to a directory containing images to merge. Can be used instead of listing files individually. | | -r, --recursive | false | Include images in all subdirectories of the specified directory recursively. | | --sh, --shuffle | false | Randomize the order of images before merging. Useful for creating visually varied grids or collages. | | -g, --gap <px> | 50 | Spacing (in pixels) between images in the layout. Applies to both horizontal and vertical gaps. | | --cr, --corner-radius <px> | 0 | How much to round the corners of each image in pixels. | | --bg, --canvas-color <hex> | #ffffff | Sets the background color of the canvas. Accepts HEX values (e.g., #000000 for black). | | --bw, --border-width <px> | 0 | Sets the width of the border in pixels. | | --bc, --border-color <hex> | #000 | Sets the color of the border, if any. Accepts HEX values (e.g., #000000 for black). | | -o, --output <file> | ./pixeli.png | Path for the merged output image. The format is inferred from the file extension (.png, .jpg, .webp, etc.). |

pixeli grid

Usage: pixeli grid [options] [files...]

The grid merge arranges images into a clean, uniform grid with fixed columns and automatic row calculation. The table below displays all of the options available to this command: | Option/Flag | Default | Description | | ----------------------------------------------- | ---------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | --ar, --aspect-ratio <width/height\|number> | 1:1 | Sets the per-image aspect ratio. Accepts ratio expressions (16/9, 4:3) or decimal values (1.777). Images are scaled as needed to match this ratio before placement. | | -w, --image-width <px> | smallest input width | Sets the final width of each processed image in the grid. The height is derived automatically based on the chosen aspect ratio. | | -c, --columns <n> | 4 | Defines how many images per row are placed in the grid. The total number of rows is calculated from the number of inputs. | | --ca, --caption | false | Enables automatic captions under each image. Captions are derived from the filename (with extensions). | | --cc, --caption-color <hex> | #000000 | HEX color value for caption text (e.g., #ffffff, #ff9900). Affects all captions uniformly. | | --mcs, --max-caption-size <pt> | 100 | Sets the maximum allowed caption font size. Useful when images are extremely large and the caption is not big enough. The renderer may auto-reduce the font size if necessary. |

pixeli masonry

Usage: pixeli masonry [options] [files...]

The masonry merge preserves each image’s natural shape, creating an organic brick-wall layout similar to Pinterest boards.

| Option/Flag | Default | Description | | ---------------------------------------------------- | ----------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------ | | --rh, --row-height <px> | smallest input height | Sets the target height for all images in a row when using horizontal flow. Images are scaled proportionally based on this height. | | --cw, --column-width <px> | smallest input width | Sets the target width for all images in a column when using vertical flow. Images are scaled proportionally based on this width. | | --cvw, --canvas-width <px> | – | Sets the fixed width of the final output canvas. Required when using a horizontal flow to know when to break a row. | | --cvh, --canvas-height <px> | – | Sets the fixed height of the final output canvas. Required when using a vertical flow to know when to break a column. | | -f, --flow <horizontal\|vertical> | horizontal | Determines the flow direction of the masonry layout. horizontal creates rows of varying widths; vertical creates columns of varying heights. | | --ha, --h-align <left\|center\|right\|justified> | justified | Controls horizontal alignment of rows when in horizontal flow. justified overfills each row and crops the final image to fill up the canvas. | | --va, --v-align <top\|middle\|bottom\|justified> | justified | Controls vertical alignment of columns when in vertical flow. justified overfills each column and crops the final image to fill up the canvas. |

pixeli template

Usage: pixeli template [options] [files...]

The template merge requires a specified JSON template file, or JSON string. Images will be placed as per the template. If a preset ID is provided, both --template and --mapping are ignored.

pixeli collage

Usage: pixeli collage [options] [files...]

The collage merge arranges images into a messy, photo-wall style grid with fixed columns and automatic row calculation. The table below displays all of the options available to this command:

| Option/Flag | Default | Description | | ----------------------------------------------- | ---------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | --ar, --aspect-ratio <width/height\|number> | 1:1 | Sets the per-image aspect ratio. Accepts ratio expressions (16/9, 4:3) or decimal values (1.777). Images are scaled as needed to match this ratio before placement. | | -w, --image-width <px> | trimmed median image width | Sets the final width of each processed image in the grid. The height is derived automatically based on the chosen aspect ratio. | | -c, --columns <n> | 4 | Defines how many images per row are placed in the grid. The total number of rows is calculated from the number of inputs. | | --op, --overlap-percentage <percent> | 25 | Defines the percentage of both vertical and horizontal overlap between any two images. A higher percentage results in tighter, more packed collages. | | --rr, --rotation-range <deg> | 7 | Defines the minimum and maximum rotation. A random rotation of this amount in degrees will be applied to each image. For no rotation, a value of 0 can be used. | | --wv, --image-width-variance <px> | 10 | Defines the random variation in image width that is added to each image width (image height variance is automatically calculated). This helps create more natural collages. A larger image variance results in more uneven image sizes. |

Full Library Documentation

Pixeli also provides functions for every merge. They can be imported like so:

import { gridMerge, masonryMerge, templageMerge, collageMerge } from 'pixeli';

All merge functions have the following signature:

interface MergeCommand<T> {
  (
  imageInputs: sharp.SharpInput[],
  options: T,
  onProgress?: (total: number, completed: number, phase: string): void;
  ): Promise<Buffer>;
}

The imageInputs parameter takes an array of valid image inputs which will be processed by sharp to create sharp instances. An image input can be a Buffer object, any subclass of Buffer, a file path string, or any other input type supported by the Sharp SharpInput interface.

The options parameter is where merge-specific options are given as an object. Each merge function has their own set of supported options.

The onProgress parameter is optional. It is a callback function which is called everytime progress is made during a merge operation. If provided, it will receive a ProgressInfo object, which contains the total number of images to be processed, the number of completed images so far, and the current phase of the merge (e.g., "Merging images" or "Initializing").

⚠️ NOTE ⚠️: The onProgress callback will be changed in upcoming versions.

The returned value of the function, if successful, is a buffer containing the final mosaic. If not successful, a MergeError will be thrown. To learn more about error handling, see wopuhfewopifhvweproihvfewpoihv MergeErrors.

gridMerge Function Options

The gridMerge function has the following set of options:

| Option | Data Type | Description | | ---------------- | --------------------- | ---------------------------------------------------------------------------------------------------------------------------------- | | shuffle | boolean | Whether to randomize the image order before merging. | | cornerRadius | number | Rounded corner radius in pixels applied to each image. | | gap | number | Gap between images in pixels. | | canvasColor | Color | Background color of the output canvas. | | borderWidth | number | Width of the border around each image in pixels. Borders are drawn internally within each image. | | borderColor | Color | Color of the border around each image. | | format | string | Output image format (e.g., png, jpeg, webp). | | aspectRatio | string \| number | Aspect ratio of each image cell. Used to calculate image height based on the given width. Examples: "16:9", "3x2", or 1.777. | | imageWidth | number \| undefined | Width of each image cell in pixels. If undefined, the median width of the input images is used. | | columns | number | Number of columns in the grid layout. | | caption | boolean | Whether to render captions under images. | | captions | string[] | Caption text for each image, in order. | | captionColor | Color | Text color used for image captions. | | maxCaptionSize | number | Maximum caption font size in pixels. |

masonryMerge Function Options

The masonryMerge function has the following set of options:

| Option | Data Type | Description | | -------------- | ---------------------------------------------- | --------------------------------------------------------------------------------------------------------------------------- | | shuffle | boolean | Whether to randomize the image order before merging. | | cornerRadius | number | Rounded corner radius in pixels applied to each image. | | gap | number | Gap between images in pixels. | | canvasColor | Color | Background color of the output canvas. | | borderWidth | number | Width of the border around each image in pixels. Borders are drawn internally within each image. | | borderColor | Color | Color of the border around each image. | | format | string | Output image format (e.g., png, jpeg, webp). | | rowHeight | number \| undefined | Height of each row in pixels. Defaults to the trimmed median image height if undefined. Only applied in horizontal layouts. | | columnWidth | number \| undefined | Width of each column in pixels. Defaults to the trimmed median image width if undefined. Only applied in vertical layouts. | | canvasWidth | number \| undefined | Width of the entire output canvas in pixels. Required when using horizontal flow. | | canvasHeight | number \| undefined | Height of the entire output canvas in pixels. Required when using vertical flow. | | flow | 'horizontal' \| 'vertical' | Orientation of the masonry layout. Determines whether items flow by rows (horizontal) or by columns (vertical). | | hAlign | 'left' \| 'center' \| 'right' \| 'justified' | Horizontal alignment of items within each row. Only applied in horizontal layouts. | | vAlign | 'top' \| 'middle' \| 'bottom' \| 'justified' | Vertical alignment of items within each column. Only applied in vertical layouts. |

templateMerge Function Options

The templateMerge function has the following set of options:

| Option | Data Type | Description | | -------------- | ---------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------- | | shuffle | boolean | Whether to randomize the image order before merging. | | cornerRadius | number | Rounded corner radius in pixels applied to each image. | | gap | number | Gap between images in pixels. | | canvasColor | Color | Background color of the output canvas. | | borderWidth | number | Width of the border around each image in pixels. Borders are drawn internally within each image. | | borderColor | Color | Color of the border around each image. | | format | string | Output image format (e.g., png, jpeg, webp). | | template | Template | An object definition describing the layout, slots, and canvas configuration used to place images. See JSON Templates for more information. |

collageMerge Function Options

The collageMerge function has the following set of options:

| Option | Data Type | Description | | -------------------- | ------------------ | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | shuffle | boolean | Whether to randomize the image order before merging. | | cornerRadius | number | Rounded corner radius in pixels applied to each image. | | canvasColor | Color | Background color of the output canvas. | | borderWidth | number | Width of the border around each image in pixels. Borders are drawn internally within each image. | | borderColor | Color | Color of the border around each image. | | format | string | Output image format (e.g., png, jpeg, webp). | | imageWidth | number | Width of each image cell in pixels. If undefined, the median input image width is used. | | aspectRatio | string \| number | Aspect ratio used to calculate image height from width. Examples: "16:9", "3x2", or 1.777. | | columns | number | Number of columns in the collage grid. | | imageWidthVariance | number | Maximum number of pixels that each image width may randomly vary from imageWidth, creating natural size variation. For example, 50 allows images to be up to ±50 pixels wider or narrower. | | overlapPercentage | number | Estimated percentage of overlap between neighboring images. Higher values create a tighter, denser collage. | | rotationRange | number | Maximum absolute rotation angle in degrees. A value of 10 produces a random rotation between -10° and +10°. |

Other

JSON Templates

JSON templates used with template merge accept a JSON object that defines a grid-based canvas layout and how content occupies it.

The layout consists of:

A canvas definition (overall grid size)
A list of slots describing how items are placed inside the grid

Logical checks are performed on the values after the template is validated. This is to ensure the mosaic can be created, for example, without any overlaps or 0 pixel-wide images.

canvas

The canvas object defines the size and structure of the grid:

{
  "canvas": {
    "width": 1200,
    "height": 800,
    "columns": 4,
    "rows": 3
  }
}

| Field | Type | Description | | --------- | ------ | ---------------------------------------------------- | | width | number | Canvas width in pixels. Must be a positive integer. | | height | number | Canvas height in pixels. Must be a positive integer. | | columns | number | Number of grid columns. Must be a positive integer. | | rows | number | Number of grid rows. Must be a positive integer. |

slots

The slots array contains a series of slots, where each slot defines where an item should appear in the grid and how many grid cells it occupies:

{
  "slots": [
    { "col": 1, "row": 1, "colSpan": 2, "rowSpan": 1 },
    { "col": 3, "row": 2, "colSpan": 1, "rowSpan": 2 }
  ]
}

| Field | Type | Description | | --------- | ------ | --------------------------------- | | col | number | Starting column index (1-based). | | row | number | Starting row index (1-based). | | colSpan | number | Number of columns the slot spans. | | rowSpan | number | Number of rows the slot spans. |

Slot Rules

All values must be positive integers.
Slots must fit within the grid:

col + colSpan - 1 ≤ columns
row + rowSpan - 1 ≤ rows

Overlapping slots will be rejected.
Slot indices start at 1, not 0.

Sample JSON Template

This is an example of a full JSON template:

{
  "canvas": {
    "width": 1200,
    "height": 1600,
    "columns": 3,
    "rows": 6,
  },
  "slots": [
    { "col": 1, "row": 1, "colSpan": 2, "rowSpan": 2 },
    { "col": 3, "row": 1, "colSpan": 1, "rowSpan": 1 },
    { "col": 3, "row": 2, "colSpan": 1, "rowSpan": 1 },
    { "col": 1, "row": 3, "colSpan": 1, "rowSpan": 2 },
    { "col": 2, "row": 3, "colSpan": 2, "rowSpan": 2 },
    { "col": 1, "row": 5, "colSpan": 3, "rowSpan": 2 }
  ]
}

Note that the canvas.background and canvas.gap properties are optional. If they are not provided, the defaults from the CLI options will be used. If both the CLI and template options exists, the template options take priority.

All Supported Input Formats

webp
gif
jpeg
jpg
png
tiff
avif
svg

All Supported Output Formats

webp
gif
jpeg
jpg
png
tiff
avif

Pixel Limits

Generating extremely large images significantly reduces speed, and may also lead to pixel limit errors. All image formats have a maximum width and height, and if the created image exceeds those resolution limits, you will receive an error:

| Format | Typical Extension(s) | Max Width × Height | Notes | | ---------------------------- | -------------------- | ---------------------------------------------------- | -------------------------------------------------------------------------------------------------- | | JPEG / JPG | .jpg, .jpeg | 65,535 × 65,535 px | Standard limit from JFIF/JPEG. No alpha. | | PNG | .png | ~2,147,483,647 × 2,147,483,647 px | Theoretical spec limit; real-world memory limits apply. Supports transparency. | | WebP | .webp | 16,383 × 16,383 px | Format standard limit — smaller than PNG/JPEG. | | GIF | .gif | 65,536 × 65,536 px | - | | BMP | .bmp | 32,767×32,767 or ~2,147,483,647×2,147,483,647 px | Depends on version/fields. | | TIFF | .tif, .tiff | 4,294,967,295 × 4,294,967,295 px (theoretical) | Very large; may be limited by software or memory. |

Error Handling

All errors produced by this library are instances of the MergeError class, which extends the Error class.

In addition to the inherited message property, the MergeError class also has a context object parameter attached to it, where there is a type and an optional cause property. Consider the following:

throw new MergeError("Some error has occurred", {
  type: 'internal',
  cause: 'helper "trimmedMedian" failed'
});

The cause property is only used when an internal error has occurred, meaning that there is something wrong with the API.

The type property can be one of the following:

validation: One of the options provided to the merge function is incorrect or is required but not provided.
image: An invalid, corrupt, or empty image input list has been provided.
internal: An error with the interal library. Should not occur.

Colors and Transparency

CLI

Hex colors are used in the CLI.

For fully transparent images, a value of transparent is allowed. Note that the transparency of the canvas itself is depends on the output format; jpg, for example, does not have an alpha channel.

Semi-transparency is also allowed, and can be achieved with hex colors of the format #rrggbbaa, where the last two hex values represent the transparency.

Library

Colors in the library functions are either objects or hex values. The Color type is used to describe colors:

type Color = { r: number; g: number; b: number; alpha: number } | string;

Given that a color object has been used instead of a hex value, note that color.r, color.g, and color.b are all values ranging from 0 to 255, while color.alpha is a value ranging from 0 to 1.

License

This project is licensed under the MIT License.

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Readme

Pixeli (Pre-release)

Table of Contents

Installation

Quick CLI Examples

Basic Grid

Grid with Rectangular Images

Grid with 8 Columns

Contact Sheet

Masonry Layout

Template Layout

Collage Layout

Full CLI Documentation

pixeli

pixeli grid

pixeli masonry

pixeli template

pixeli collage

Full Library Documentation

gridMerge Function Options

masonryMerge Function Options

templateMerge Function Options

collageMerge Function Options

Other

JSON Templates

canvas

slots

Slot Rules

Sample JSON Template

All Supported Input Formats

All Supported Output Formats

Pixel Limits

Error Handling

Colors and Transparency

CLI

Library

License