verify align hash output with imagehash

[aastopher]

aHash

• Reversed Bit Order:
  Now uses 1 << (63 - i) so that the most significant bit corresponds to the first pixel, matching imagehash’s convention.

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mHash

• Reversed Bit Order:
  Bit order is reversed (using 1 << (63 - i)) to align with other hash types.
• Optimized Median Calculation:
  Uses Rust’s select_nth_unstable to compute the median in O(n) time instead of a full sort.

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dHash

• Optimized Loop Structure:
  Retrieves the first pixel outside the inner loop (iterating from x = 1 to 8) to avoid redundant calls.

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pHash

• Refined DCT Processing:
  Applies the DCT row‑wise and then column‑wise in place using a fixed‑size temporary array.
• DC Exclusion in Median Calculation:
  Extracts the top‑left 8×8 DCT coefficients and excludes the DC component when computing the median.
• O(n) Median Computation:
  Uses select_nth_unstable_by to find median in O(n).
• Reversed Bit Order:
  Final hash bits are reversed (using 1 << (63 - i)) for consistency with the other algorithms.
• Result:
  Produces a pHash that is consistent with imagehash.

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wHash (Wavelet Hash)

• Reversed Bit Order:
  Now uses 1 << (63 - i) so that the most significant bit corresponds to the first pixel, matching imagehash’s convention.
• Haar Transform via dwt Crate:
  Implement Haar transform functions from the dwt crate.
• Zeroing DC Coefficient:
  Immediately zero out the DC coefficient after forward transform.
• O(n) Median Calculation:
  Clones transformed pixel vector and uses select_nth_unstable_by to find median in O(n).
• Hash Generation:
  Iterates over the reconstructed coefficients from the inverse Haar transform, setting bits based on the median, to conform to imagehash’s output.
• Result:
  Produces a wHash that is consistent with imagehash.

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Each change was made to improve performance, and ensure consistent bit ordering across all hash types, and simplify the implementations and align hash output with imagehash for consistency.

[deepsource-io]

Here's the code health analysis summary for commits e2a4b89..f9e65e5. View details on DeepSource ↗.

Analysis Summary

Analyzer	Status	Summary	Link
Rust	✅ Success		View Check ↗

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[codspeed-hq]

CodSpeed Performance Report

Merging #26 will not alter performance

_{Comparing stage (f9e65e5) with main (e2a4b89)}

Summary

✅ 10 untouched benchmarks

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (350018c) to head (f9e65e5).
Report is 22 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #26   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            5         5           
  Lines          186       174   -12     
=========================================
- Hits           186       174   -12     

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