Overview
Introduction
Need a plain background image at an exact size: a placeholder, a design mockup, or a brand-color test swatch? This generates one in one step.
Everything runs client-side; the resulting JPG is generated and encoded entirely in your browser.
What Is Custom JPG Generator?
A solid/gradient fill generator that builds a pixel buffer of any requested width and height, filled with a single hex color or, if a second color is provided, a smooth linear gradient between the two.
The result is encoded as a standard, fully opaque JPEG ready to download.
How Custom JPG Generator Works
For each row of the output canvas, the tool computes how far that row is between the top (0%) and bottom (100%) of the image, and linearly interpolates between the first and second color by that fraction; every pixel in a given row gets the same interpolated color.
If no second color is supplied, every row uses the exact same first color, producing a uniform solid fill.
When To Use Custom JPG Generator
Use it to generate a quick placeholder background image at a specific size for a design mockup or prototype.
It's also handy for producing a brand-color test swatch, or a simple gradient background for a banner or social post.
Often used alongside Random JPG Generator, JPG Generator by Color Name and Custom PNG Creator.
Features
Advantages
- Generates an exact pixel size on demand, with no need to open a design tool.
- Supports both flat solid colors and smooth two-color gradients from the same tool.
- Runs entirely client-side and downloads a real, standard JPEG file.
Limitations
- Only a straight top-to-bottom gradient direction is supported; diagonal or radial gradients aren't available here.
- There's no support for more than two gradient stops in one pass.
Examples
Best Practices & Notes
Best Practices
- Use common social/banner dimensions (like 1200x630) when generating a placeholder meant for a specific platform.
- Pick two colors with a similar lightness for the smoothest-looking gradient transition.
Developer Notes
generateCustomJpg is adapted from custom-png-creator.ts's solid-fill approach, replacing its border feature with an optional linear vertical gradient (row-by-row lerp using the shared clampByte helper) since JPG's spec calls for a simple gradient option instead of a border.
Custom JPG Generator Use Cases
- Generating an exact-size placeholder background for a design mockup
- Creating a brand-color test swatch at a specific resolution
- Producing a simple gradient banner background for a social post
Common Mistakes
- Expecting a diagonal or radial gradient; only a top-to-bottom linear blend is supported.
- Forgetting the # prefix isn't required: both '#3366CC' and '3366CC' work identically.
Tips
- Leave the second color field blank whenever you just want a plain solid fill.
- Add a border afterward with the JPG Border Adder if you need a framed placeholder.