# Documentation

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# qtgetblk

## Syntax

```[vals, r, c] = qtgetblk(I, S, dim) [vals, idx] = qtgetblk(I, S, dim) ```

## Description

`[vals, r, c] = qtgetblk(I, S, dim)` returns in `vals` an array containing the `dim`-by-`dim` blocks in the quadtree decomposition of `I`. `S` is the sparse matrix returned by `qtdecomp`; it contains the quadtree structure. `vals` is a `dim`-by-`dim`-by-`k` array, where `k` is the number of `dim`-by-`dim` blocks in the quadtree decomposition; if there are no blocks of the specified size, all outputs are returned as empty matrices. `r` and `c` are vectors containing the row and column coordinates of the upper left corners of the blocks.

`[vals, idx] = qtgetblk(I, S, dim)` returns in `idx` a vector containing the linear indices of the upper left corners of the blocks.

## Class Support

`I` can be of class `logical`, `uint8`, `uint16`, `int16`, `single`, or `double`. `S` is of class `sparse`.

## Examples

```I = [1 1 1 1 2 3 6 6 1 1 2 1 4 5 6 8 1 1 1 1 10 15 7 7 1 1 1 1 20 25 7 7 20 22 20 22 1 2 3 4 20 22 22 20 5 6 7 8 20 22 20 20 9 10 11 12 22 22 20 20 13 14 15 16]; S = qtdecomp(I,5); [vals,r,c] = qtgetblk(I,S,4)```

## Tips

The ordering of the blocks in `vals` matches the columnwise order of the blocks in `I`. For example, if `vals` is 4-by-4-by-2, `vals(:,:,1)` contains the values from the first 4-by-4 block in `I`, and `vals(:,:,2)` contains the values from the second 4-by-4 block.