### ImageMagick version

7.1.1.12

### Operating system

Linux

### Operating system, version and so on

ArchLinux 6.3.8-arch1-1

### Description

Hi, the `-separate` flag doesn't seem to be working correctly in 7.1.1.12. See attached image below.

I first found this when running `convert file.jpg -colorspace HSI -channel g -separate +channel -format "%[fx:mean]" info:` to extract mean saturation to determine whether an image is grayscale. In 7.1.1.12 the command outputs `0.2560250.2833310.412341` (means of all 3 channels) instead of just `0.283331`.

### Steps to Reproduce

Run the sample commands from [the docs](https://legacy.imagemagick.org/Usage/color_basics/#separate):

```
convert rose: -channel R -separate separate_red.gif
convert rose: -channel G -separate separate_green.gif
convert rose: -channel B -separate separate_blue.gif
```

### Images

![blah](https://github.com/ImageMagick/ImageMagick/assets/69230639/6e712599-b6e9-4a49-b9d6-c9911d9eb542)

-channel -separate bug in 7.1.1.12
This is a GitHub Issue
repo:ImageMagick
owner:ImageMagick
Title : -channel -separate bug in 7.1.1.12
Issue date:

--- start body ---
### ImageMagick version

7.1.1.12

### Operating system

Linux

### Operating system, version and so on

ArchLinux 6.3.8-arch1-1

### Description

Hi, the `-separate` flag doesn't seem to be working correctly in 7.1.1.12. See attached image below.

I first found this when running `convert file.jpg -colorspace HSI -channel g -separate +channel -format "%[fx:mean]" info:` to extract mean saturation to determine whether an image is grayscale. In 7.1.1.12 the command outputs `0.2560250.2833310.412341` (means of all 3 channels) instead of just `0.283331`.

### Steps to Reproduce

Run the sample commands from [the docs](https://legacy.imagemagick.org/Usage/color_basics/#separate):

```
convert rose: -channel R -separate separate_red.gif
convert rose: -channel G -separate separate_green.gif
convert rose: -channel B -separate separate_blue.gif
```

### Images

![blah](https://github.com/ImageMagick/ImageMagick/assets/69230639/6e712599-b6e9-4a49-b9d6-c9911d9eb542)

--- end body ---
