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Julia code: shifting and scaling a matrix
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| using Images | |
| """ | |
| B = shift_lr(A, k) | |
| Shift `A` by `k` columns. If `k` is positive, shift to the | |
| right by inserting `k` columns on the left. If `k` is | |
| negative, shift to the left by inserting `k` columns | |
| on the right. | |
| """ | |
| function shift_lr(A::AbstractMatrix, k::Integer) | |
| k == 0 && return A | |
| m, n = size(A) | |
| if abs(k) > n | |
| @error "Cannot shift matrix with $n columns by $k columns" | |
| end | |
| fill_val = (k > 0 ? A[1] : A[end]) | |
| F = fill(fill_val, m, abs(k)) | |
| B = (k > 0 ? [F A[:, 1:(n - k)]] : [A[:, (abs(k) + 1):n] F]) | |
| return B | |
| end | |
| """ | |
| Shift `A` by `k` rows. If `k` is positive, shift upward by | |
| inserting `k` rows on the bottom. If `k` is | |
| negative, shift downward by inserting `k` rows | |
| on top. | |
| """ | |
| function shift_ud(A::AbstractMatrix, k::Integer) | |
| k == 0 && return A | |
| m, n = size(A) | |
| if abs(k) > m | |
| @error "Cannot shift matrix with $m rows by $k rows." | |
| end | |
| fill_val = (k > 0 ? A[1] : A[end]) | |
| F = fill(fill_val, abs(k), n) | |
| B = (k > 0 ? [A[(k + 1):m, :]; F] : [F; A[1:(m - abs(k)), :]]) | |
| return B | |
| end | |
| """ | |
| B = scale(A, α) | |
| Use `Images.imresize` to resize `A` by ratio `α`, | |
| preserving its original dimensions. | |
| """ | |
| function scale(A::AbstractMatrix, α::Float64) | |
| α == 1.0 && return A | |
| m, n = size(A) | |
| As = imresize(A; ratio=α) | |
| ms, ns = size(As) | |
| if α < 1.0 | |
| fill_rows = m - ms | |
| fill_cols = n - ns | |
| bottom = fill_rows / 2 |> ceil |> Int | |
| left = fill_cols / 2 |> ceil |> Int | |
| fill_value = A[1] | |
| B = fill(fill_value, m, n) .|> Float64 | |
| B[(bottom + 1):(bottom + ms), (left + 1):(left + ns)] = As | |
| else | |
| excess_rows = ms - m | |
| excess_cols = ns - n | |
| bottom = excess_rows / 2 |> ceil |> Int | |
| left = excess_cols / 2 |> ceil |> Int | |
| B = As[(bottom + 1):(bottom + m), (left + 1):(left + n)] | |
| end | |
| return B | |
| end |
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