jimp-dev/jimp

Even sized kernel support

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#749 opened on Jun 7, 2019

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enhancementhelp wanted

Description

Is your feature request related to a problem? Please describe. It would be useful to have even sized kernel support for convolution etc.

Describe the solution you'd like The implementation could follow Matlabs imfilter/conv2 algorithm. Imfilter(M, k) result is same as conv2(M, k, 'same').

Matlabs documentation states: "If you specify an even-sized kernel h, then the center of the kernel is floor((size(h) + 1)/2).

For example, the center of 4-element filter [0.25 0.75 -0.75 -0.25] is the second element, 0.75. This filter gives identical results as filtering with the 5-element filter [0 0.25 0.75 -0.75 -0.25]."

https://se.mathworks.com/help/images/ref/imfilter.html

Contributor guide

Tech stack
javascriptnodejs
Domain
backenddata
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Convolution basicsJavaScript
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
45
Research direction
Examine the current convolution implementation in jimp (likely in a plugin like plugin rotate or plugin blur). The issue requests adding support for even sized kernels following Matlab's conv2 algorithm, where the center is floor((size(h)+1)/2). A good starting point is to review the existing convolution code and modify it to handle even sized kernels by aligning the center to floor((size+1)/2). Testing should include cases with 2x2 and 4x1 kernels to ensure output matches expected results.