measureObjects {cytomapper} | R Documentation

## Compute morphological and intensity features from objects on images.

### Description

For each object (e.g. cell) identified by segmentation, the `measureObjects` function computes intensity features (also referred to as basic features; e.g. mean intensity), shape features (e.g. area), moment features (e.g. position) and haralick features. These features are returned in form of a SingleCellExperiment object.

### Usage

    measureObjects(
      mask,
      image,
      img_id,
      feature_types = c("basic", "shape", "moment"),
      basic_feature = "mean",
      basic_quantiles = NULL,
      shape_feature = c("area", "radius.mean"),
      moment_feature = c("cx", "cy", "majoraxis", "eccentricity"),
      haralick_feature = NULL,
      haralick_nbins = 32,
      haralick_scales = c(1, 2),
      BPPARAM = SerialParam()
    )

### Arguments

`mask` | a `CytoImageList` object containing single-channel `Image` or `HDF5Array` objects. Segmentation masks must contain integer pixel values where groups of pixels correspond to objects.
`image` | a `CytoImageList` object containing single or multi-channel `Image` or `HDF5Array` objects, where each channel indicates the measured pixel intensities.
`img_id` | character specifying the `mcols(image)` and `mcols(mask)` entry, in which the image IDs are stored.
`feature_types` | character vector or string indicating which features to compute. Needs to contain `"basic"`. Optionally, `"shape"`, `"moment"` and `"haralick"` are allowed. Default `"basic"`, `"shape"` and `"moment"`.
`basic_feature` | string indicating which intensity measurement per object and channel should be used to populate the `counts(x)` slot; where `x` is the returned `SingleCellExperiment` object. Default `"mean"` but `"sd"`, `"mad"` and `"q*"` allowed. Here, `*` indicates the computed quantile (see `basic_quantiles`).
`basic_quantiles` | numeric vector or single number indicating which quantiles to compute. Default none.
`shape_feature` | string or character vector specifying which shape features to compute. Default `"area"` and `"radius.mean"`. Allowed entries are: `"area"`, `"perimeter"`, `"radius.mean"`, `"radius.sd"`, `"radius.max"`, `"radius.min"`.
`moment_feature` | string or character vector indicating which moment features to compute. Default `"cx"`, `"cy"`, `"majoraxis"`, and `"eccentricity"`. Other allowed features are `"theta"`. Here moment features are only computed on the segmentation mask without incorporating pixel intensities. Therefore, `"cx"` and `"cy"` are the x and y coordinates of the cell centroids.
`haralick_feature` | string or character vector indicating which haralick features to compute. Default none. Allowed are the 13 haralick features: `"asm"`, `"con"`, `"cor"`, `"var"`, `"idm"`, `"sav"`, `"sva"`, `"sen"`, `"ent"`, `"dva"`, `"den"`, `"f12"`, `"f13"`
`haralick_nbins` | an integer indicating the number of bins used to compute the haralick matrix. Pixel intensities are binned in `haralick_nbins` discrete gray levels before computing the haralick matrix.
`haralick_scales` | an integer vector indicating the number of scales (distance at which to consider neighbouring pixels) to use to compute the haralick features.
`BPPARAM` | parameters for parallelised processing of images. See `MulticoreParam` for information on how to use multiple cores for parallelised processing.

### Value

A SingleCellExperiment object (see details)

### The returned SingleCellExperiment objects

The returned SingleCellExperiment object `sce` contains a single assay. This assay contains individual objects in columns and channels in rows. Each entry summarises the intensities per object and channel. This summary statistic is typically the mean intensity per object and channel. However, other summary statistics can be computed. When the mean intensity per object and channel is computed (default), the assay is accessible via `counts(sce)`. Otherwise, the assay needs to be accessed via `assay(sce, "counts_*")`, where `*` indicates the argument to `basic_feature`.

The `colData(x)` entry is populated by the computed shape, moment and haralick features per object. The prefix of the feature names indicate whether these features correspond to shape (`s.`), moment (`m.`) or haralick (`h.`) features. Default features are the following:

- s.areaobject size in pixels

- s.radius.meanmean object radius in pixels

- m.cxx centroid position of object

- m.cyy centroid position of object

- m.majoraxismajor axis length in pixels of elliptical fit

- m.eccentricityelliptical eccentricity. 1 meaning straight line and 0 meaning circle.

### Computing quantiles

Sometimes it can be useful to describe the summarised pixel intensity per object and channel not in terms of the mean but some quantile of the pixel distribution. For example, to compute the median pixel intensity per object and channel, set `basic_feature = "q05"` and `basic_quantiles = 0.5`.

### Author(s)

Nils Eling (nils.eling@dqbm.uzh.ch),

### See Also

`computeFeatures`, for detailed explanation for the computed features. https://earlglynn.github.io/RNotes/package/EBImage/Haralick-Textural-Features.html for more discussion on the haralick features

### Examples

    # Standard example
    data(pancreasImages)
    data(pancreasMasks)

    sce <- measureObjects(pancreasMasks, pancreasImages, img_id = "ImageNb")
    sce

    # Compute only intensity feature
    sce <- measureObjects(pancreasMasks, pancreasImages, img_id = "ImageNb",
                            feature_types = "basic")
    colData(sce)

    # Visualize on segmentation masks
    plotCells(pancreasMasks, object = sce, img_id = "ImageNb",
                cell_id = "object_id", colour_by = "PIN")

[Package cytomapper version 1.4.1 Index]