Grayscale / Sepia Image Filter
Apply grayscale or sepia filters to an uploaded image.
Overview
The Grayscale / Sepia Image Filter applies one of two classic tonal treatments to an uploaded picture: a luminance-weighted grayscale conversion that mimics black-and-white film, or a warm sepia wash that recalls vintage photography. Drop in a JPEG, PNG or WebP and the tool returns a re-encoded copy in the same format.
It is useful for moodboards, blog hero images, social-media throwbacks, and anyone who needs a quick black and white photo converter without launching a full editor. The sepia option is popular for old-style portraits, museum-style document scans, and "remember when" social posts.
How it works
Grayscale conversion uses Rec. 709 luminance coefficients — each output pixel is 0.2126 R + 0.7152 G + 0.0722 B — which weights green more heavily than red and blue to match human perceptual sensitivity. The same value is written to all three channels of the output, producing a neutral monochrome rendition that beats a naive (R+G+B)/3 average.
Sepia applies a fixed 3x3 matrix to the RGB triplet: roughly (0.393, 0.769, 0.189) / (0.349, 0.686, 0.168) / (0.272, 0.534, 0.131). The result tints highlights toward warm amber and shadows toward cool brown, the classic colour cast of photographs printed with silver-sulphide-toned papers. Values that exceed 255 are clamped.
Examples
Before: portrait.jpg (RGB photo)
After: portrait-bw.jpg (luminance-weighted grayscale)
Before: skyline.jpg (vivid sunset)
After: skyline-sepia.jpg (warm amber-tinted)
Before: screenshot.png (UI screenshot)
After: screenshot-bw.png (useful for print-friendly docs)
FAQ
Why isn't my grayscale a simple average?
Averaging makes red and blue feel artificially bright, which mis-represents how the eye perceives the scene. Rec. 709 weighting matches human luminance sensitivity and matches what cameras and TVs use.
Will the output be smaller in file size?
Slightly. JPEG and PNG both still store three channels (or one with a colour profile), so the saving comes from the lower chroma variance rather than a channel-count reduction.
Can I adjust the sepia intensity?
The bundled matrix produces the canonical warm tone. To dial it back, blend the sepia output with the original using a separate compositing step.
Does it preserve the alpha channel?
Yes — alpha is passed through untouched so cut-outs and shadows remain transparent in the output.
What about colour profiles?
The output is written as untagged sRGB. If your source carries a wide-gamut ICC profile, the colours are first converted to sRGB before the filter runs.