# Image Channel Merger

Combine three or four grayscale images into the channels of one picture. Upload the files in order, red, green, blue and optionally alpha, and the tool joins them into a single RGB or RGBA PNG. Color uploads are converted to grayscale first and later files are resized to match the first. Perfect for packed game textures, false color imaging, channel editing and creative color effects.

## Frequently asked questions

### In which order should I upload the files?

The first file becomes the red channel, the second the green channel and the third the blue channel. An optional fourth file becomes the alpha channel, where white is opaque and black is transparent. The first file is the base and sets the size of the result.

### How many files can I upload?

Upload three files for an RGB image or four files for an RGBA image with transparency. Fewer than three or more than four files are rejected with a message. Each file may be up to 5 MB.

### Can I use color images as input?

Yes, every upload is converted to grayscale with the standard Rec. 709 luminance weights before it is used as a channel. For exact values, upload images that are already grayscale, such as channels saved with the Image Channel Extractor.

### What if the images have different sizes?

The second, third and fourth images are resized to exactly the width and height of the first image, without keeping their aspect ratio. For best results, prepare all channels at the same size. Images over 4000 pixels on a side are first scaled down to fit.

### What is channel packing?

Game engines and 3D tools often store several grayscale maps, such as ambient occlusion, roughness and metalness, in the red, green and blue channels of one texture to save memory. This tool builds such packed textures from separate maps in one step.

### How do I create false color images?

Upload grayscale images captured with different filters or bands, for example infrared, red and green, in the order you want them displayed. Astronomers and remote sensing users combine bands this way to reveal details invisible in normal color.

### What is the output format and name?

The result is a lossless PNG named after the first uploaded file. It has three channels, or four with the alpha file. Transparency of the uploaded files themselves is ignored.

### Which formats can I upload?

JPEG, PNG, GIF, WebP, TIFF and AVIF images are accepted for each channel. Animated files use their first frame.

### Can I swap channels of an existing photo?

Yes, extract its channels with the Image Channel Extractor and upload them here in a different order. For a quicker swap in one step, the Image Channel Mixer accepts a matrix such as 0 0 1 / 0 1 0 / 1 0 0.

### What engine joins the channels?

The channels are combined with the joinChannel operation of the sharp library on libvips. The values of each grayscale input are copied exactly into its channel.

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