ADDITIONAL SYSTEM INFORMATION :
It occurs both on Java 8 and Java 23

A DESCRIPTION OF THE PROBLEM :
While an 8-bit greyscale image is recognized correctly as ColorSpace.TYPE_GRAY, an 1-bit monochrome image is recognized as ColorSpace.TYPE_RGB.


STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. Create a binary image (i.e. an image that only contains black and white and no other greyscale values) from a color image as following:
magick test.24bit.png test.converted.pbm
magick test.converted.pbm test.converted.monochrome.png
2. Execute code further below


EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
While the BufferedImage.getType() returns 12 which corresponds to BufferedImage.TYPE_BYTE_BINARY, both ImageReader.getRawImageType(...).getColorModel().getColorSpace().getType() returned the same result as ImageIO.read(...).getColorModel().getColorSpace().getType() which is TYPE_RGB.
More appropriate would be to return ColorSpace.TYPE_GRAY (because like grey images, binary images have only a single color channel).
(An alternative could be to introduce another enum value which would represent a monochrome binary (i.e. representing only black and white) images).

ACTUAL -
ImageReader.getRawImageType(...).getColorModel().getColorSpace().getType() returned the same result as ImageIO.read(...).getColorModel().getColorSpace().getType() which is TYPE_RGB.
You will seee the following output from the test program in the attached zip:
16:38:10.751 [main] DEBUG com.mycompany.colorspace.test.ColorSpaceRecognition - ImageIO.createImageInputStream(/test.converted.monochrome.png)
16:38:10.927 [main] DEBUG com.mycompany.colorspace.test.ColorSpaceRecognition - rawImageType.getColorModel().getColorSpace().getType(): 5 (5=RGB, 6=GRAY, 3=YCbCr)
16:38:10.927 [main] DEBUG com.mycompany.colorspace.test.ColorSpaceRecognition - rawImageType.getColorModel().getPixelSize(): 1
16:38:10.927 [main] DEBUG com.mycompany.colorspace.test.ColorSpaceRecognition - rawImageType.getColorModel().getNumColorComponents(): 3
...
16:38:10.927 [main] DEBUG com.mycompany.colorspace.test.ColorSpaceRecognition - rawImageType.getColorModel().getColorSpace().isCS_sRGB(): true
16:38:10.927 [main] DEBUG com.mycompany.colorspace.test.ColorSpaceRecognition - ImageIO.read(/test.converted.monochrome.png)
16:38:10.937 [main] DEBUG com.mycompany.colorspace.test.ColorSpaceRecognition - image.getColorModel().getColorSpace().getType(): 5 (5=RGB, 6=GRAY, 3=YCbCr)
16:38:10.937 [main] DEBUG com.mycompany.colorspace.test.ColorSpaceRecognition - image.getType(): 12
16:38:10.937 [main] DEBUG com.mycompany.colorspace.test.ColorSpaceRecognition - image.getColorModel().getPixelSize(): 1
...
16:38:10.937 [main] DEBUG com.mycompany.colorspace.test.ColorSpaceRecognition - image.getColorModel().getColorSpace().isCS_sRGB(): true
16:38:10.937 [main] DEBUG com.mycompany.colorspace.test.ColorSpaceRecognition - image.getSampleModel().getNumBands(): 1


---------- BEGIN SOURCE ----------
package com.mycompany.colorspace.test;

import com.google.common.io.ByteStreams;
import java.awt.color.ColorSpace;
import java.awt.image.BufferedImage;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.Iterator;
import javax.imageio.ImageIO;
import javax.imageio.ImageReader;
import javax.imageio.ImageTypeSpecifier;
import javax.imageio.stream.ImageInputStream;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class ColorSpaceRecognition {

    private static final Logger logger = LoggerFactory.getLogger(ColorSpaceRecognition.class);

    public static void main(String[] args) throws IOException {
        // Created using:
        // magick test.24bit.png test.converted.pbm
// magick test.converted.pbm test.converted.monochrome.png
        printColorSpaceInfos("/test.converted.monochrome.png");
    }

    private static void printColorSpaceInfos(String resourceName) throws IOException {
        printRawColorSpace(resourceName);
        printNonRawColorSpace(resourceName);
    }

    private static void printNonRawColorSpace(String resourceName) throws IOException {
        logger.debug("ImageIO.read({})", resourceName);
        BufferedImage image = ImageIO.read(new ByteArrayInputStream(getResourceAsBytes(resourceName)));
        if (image == null) {
            throw new RuntimeException("image format not supported");
        }
        logger.debug(" image.getColorModel().getColorSpace().getType(): {} ({}=RGB, {}=GRAY, {}=YCbCr)",
                image.getColorModel().getColorSpace().getType(), ColorSpace.TYPE_RGB, ColorSpace.TYPE_GRAY, ColorSpace.TYPE_YCbCr);

        logger.debug(" image.getType(): {}", image.getType());
        logger.debug(" image.getColorModel().getPixelSize(): {}",
                image.getColorModel().getPixelSize());
        logger.debug(" image.getColorModel().getNumColorComponents(): {}",
                image.getColorModel().getNumColorComponents());
        logger.debug(" image.getColorModel().getComponentSize().length: {}",
                image.getColorModel().getComponentSize().length);
        for (int i = 0; i < image.getColorModel().getComponentSize().length; i++) {
            logger.debug(" image.getColorModel().getComponentSize()[{}]: {}", i,
                    image.getColorModel().getComponentSize()[i]);
        }
        logger.debug(" image.getColorModel().getColorSpace().isCS_sRGB(): {}",
                image.getColorModel().getColorSpace().isCS_sRGB());
        logger.debug(" image.getSampleModel().getNumBands(): {}",
                image.getSampleModel().getNumBands());
    }

    private static void printRawColorSpace(String resourceName) throws IOException {

        logger.debug("ImageIO.createImageInputStream({})", resourceName);
        try (ImageInputStream input
                = ImageIO.createImageInputStream(new ByteArrayInputStream(getResourceAsBytes(resourceName)))) {
            Iterator<ImageReader> readers = ImageIO.getImageReaders(input);
            if (!readers.hasNext()) {
                throw new RuntimeException("image format not supported");
            } else {
                ImageReader reader = readers.next();

                try {
                    reader.setInput(input);

                    ImageTypeSpecifier rawImageType = reader.getRawImageType(0);
                    if (rawImageType == null) {
                        logger.debug(" rawImageType: null");
                    } else {
                        logger.debug(" rawImageType.getColorModel().getColorSpace().getType(): {} ({}=RGB, {}=GRAY, {}=YCbCr)",
                                rawImageType.getColorModel().getColorSpace().getType(), ColorSpace.TYPE_RGB, ColorSpace.TYPE_GRAY, ColorSpace.TYPE_YCbCr);
                        logger.debug(" rawImageType.getColorModel().getPixelSize(): {}",
                                rawImageType.getColorModel().getPixelSize());
                        logger.debug(" rawImageType.getColorModel().getNumColorComponents(): {}",
                                rawImageType.getColorModel().getNumColorComponents());
                        logger.debug(" rawImageType.getColorModel().getComponentSize().length: {}",
                                rawImageType.getColorModel().getComponentSize().length);
                        for (int i = 0; i < rawImageType.getColorModel().getComponentSize().length; i++) {
                            logger.debug(" rawImageType.getColorModel().getComponentSize()[{}]: {}", i,
                                    rawImageType.getColorModel().getComponentSize()[i]);
                        }
                        logger.debug(" rawImageType.getColorModel().getColorSpace().isCS_sRGB(): {}",
                                rawImageType.getColorModel().getColorSpace().isCS_sRGB());
                    }
                } finally {
                    reader.dispose();
                }
            }
        }
    }

    private static byte[] getResourceAsBytes(String resourceName) {
        return getResourceAsBytes(resourceName, ColorSpaceRecognition.class);
    }

    private static byte[] getResourceAsBytes(String resourceName, Class<?> clazz) {
        try (InputStream in = clazz.getResourceAsStream(resourceName)) {
            if (in == null) {
                throw new RuntimeException("Resource '" + resourceName
                        + "' could not be loaded with ClassLoader for " + clazz.getCanonicalName());
            }
            return ByteStreams.toByteArray(in);
        } catch (IOException ex) {
            throw new RuntimeException(ex);
        }
    }
}

---------- END SOURCE ----------