A DESCRIPTION OF THE PROBLEM :
The BITMAPFILEHEADER.bfOffBits [1] field specifies the starting offset of the pixel data in a BMP file. Thus it is possible to have a gap after the BITMAPINFOHEADER + the following color table [2] before the pixel data (see the visualization [3] from Wikipedia, for example). BMPImageReader fails to read such files:

    javax.imageio.IIOException: java.lang.IllegalArgumentException: Raster BytePackedRaster: width = 32 height = 32 #channels 1 xOff = 0 yOff = 0 is incompatible with ColorModel IndexColorModel: #pixelBits = 4 numComponents = 3 color space = java.awt.color.ICC_ColorSpace@4b6995df transparency = 1 transIndex = -1 has alpha = false isAlphaPre = false
     at java.desktop/java.awt.image.BufferedImage.<init>(BufferedImage.java:622)
     at java.desktop/com.sun.imageio.plugins.bmp.BMPImageReader.read(BMPImageReader.java:909)
     at java.desktop/javax.imageio.ImageIO.read(ImageIO.java:1470)
     ...

When the color table contains fewer colors than necessary to address full N-bits, and the gap fits into the remainder of a full color table, BMPImageReader doesn't fail but incorrectly includes the gap data as part of the color table.

[1] https://learn.microsoft.com/en-us/windows/win32/api/wingdi/ns-wingdi-bitmapfileheader#:~:text=bfoffbits,-The%20offset
[2] https://learn.microsoft.com/en-us/windows/win32/api/wingdi/ns-wingdi-bitmapinfoheader#color-tables
[3] https://en.wikipedia.org/wiki/BMP_file_format#/media/File:BMPfileFormat.svg

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. Run the attached test case: "java IndexedBMPReadTest.java"
2. Observe the console output

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
```
image-2bit.bmp
-> pixelSize=1, mapSize=2
image-2bit-gap1.bmp
-> pixelSize=1, mapSize=2
image-4bit.bmp
-> pixelSize=4, mapSize=4
image-4bit-gap1a.bmp
-> pixelSize=4, mapSize=4
image-4bit-gap1b.bmp
-> pixelSize=4, mapSize=4
```

ACTUAL -
```
image-2bit.bmp
-> pixelSize=1, mapSize=2
image-2bit-gap1.bmp
javax.imageio.IIOException: java.lang.IllegalArgumentException: Raster BytePackedRaster: width = 32 height = 32 #channels 1 xOff = 0 yOff = 0 is incompatible with ColorModel IndexColorModel: #pixelBits = 1 numComponents = 3 color space = java.awt.color.ICC_ColorSpace@2cfb4a64 transparency = 1 transIndex = -1 has alpha = false isAlphaPre = false
at java.desktop/java.awt.image.BufferedImage.<init>(BufferedImage.java:622)
at java.desktop/com.sun.imageio.plugins.bmp.BMPImageReader.read(BMPImageReader.java:909)
at java.desktop/javax.imageio.ImageIO.read(ImageIO.java:1470)
...
image-4bit.bmp
-> pixelSize=4, mapSize=4
image-4bit-gap1a.bmp
-> pixelSize=4, mapSize=14
image-4bit-gap1b.bmp
javax.imageio.IIOException: java.lang.IllegalArgumentException: Raster BytePackedRaster: width = 32 height = 32 #channels 1 xOff = 0 yOff = 0 is incompatible with ColorModel IndexColorModel: #pixelBits = 4 numComponents = 3 color space = java.awt.color.ICC_ColorSpace@2cfb4a64 transparency = 1 transIndex = -1 has alpha = false isAlphaPre = false
at java.desktop/java.awt.image.BufferedImage.<init>(BufferedImage.java:622)
at java.desktop/com.sun.imageio.plugins.bmp.BMPImageReader.read(BMPImageReader.java:909)
at java.desktop/javax.imageio.ImageIO.read(ImageIO.java:1470)
...
```


---------- BEGIN SOURCE ----------
---"IndexedBMPReadTest.java"
import java.io.ByteArrayInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Base64;

import java.awt.image.BufferedImage;
import java.awt.image.IndexColorModel;
import javax.imageio.ImageIO;

public class IndexedBMPReadTest {

    public static void main(String[] args) throws Exception {
        Object[][] files = {
            { "image-2bit.bmp", IMAGE_2BIT },
            { "image-2bit-gap1.bmp", IMAGE_2BIT_GAP1 },
            { "image-4bit.bmp", IMAGE_4BIT },
            { "image-4bit-gap1a.bmp", IMAGE_4BIT_GAP1A },
            { "image-4bit-gap1b.bmp", IMAGE_4BIT_GAP1B }
        };
        for (Object[] params : files) {
            readImage((String) params[0], (byte[]) params[1]);
        }
    }

    private static void readImage(String name, byte[] data) throws IOException {
        System.out.println(name);
        try (FileOutputStream fout = new FileOutputStream(name)) {
            fout.write(data);
        }
        try {
            BufferedImage image = ImageIO.read(new ByteArrayInputStream(data));
            IndexColorModel cm = (IndexColorModel) image.getColorModel();
            System.out.printf("\t-> pixelSize=%d, mapSize=%d%n", cm.getPixelSize(), cm.getMapSize());
        } catch (IOException e) {
            e.printStackTrace(System.err);
        }
    }

    static final byte[] IMAGE_2BIT = Base64.getMimeDecoder().decode(
            "Qk2+AAAAAAAAAD4AAAAoAAAAIAAAACAAAAABAAEAAAAAAIAAAAATCwAAEwsA"
            + "AAIAAAACAAAAAAAAAP///wD///////AP//+AAf//AAD//AAAP/gAAB/wAAAP"
            + "8AAAD+AAAAfAAAADwAAAA8AAAAOAAAABgAAAAYAAAAGAAAABgAAAAYAAAAGA"
            + "AAABgAAAAcAAAAPAAAADwAAAA+AAAAfwAAAP8AAAD/gAAB/8AAA//wAA//+A"
            + "Af//8A///////w==");

    static final byte[] IMAGE_2BIT_GAP1 = Base64.getMimeDecoder().decode(
            "Qk3CAAAAAAAAAEIAAAAoAAAAIAAAACAAAAABAAEAAAAAAIAAAAATCwAAEwsA"
            + "AAIAAAACAAAAAAAAAP///wCqqqqq///////wD///gAH//wAA//wAAD/4AAAf"
            + "8AAAD/AAAA/gAAAHwAAAA8AAAAPAAAADgAAAAYAAAAGAAAABgAAAAYAAAAGA"
            + "AAABgAAAAYAAAAHAAAADwAAAA8AAAAPgAAAH8AAAD/AAAA/4AAAf/AAAP/8A"
            + "AP//gAH///AP//////8=");

    static final byte[] IMAGE_4BIT = Base64.getMimeDecoder().decode(
            "Qk1GAgAAAAAAAEYAAAAoAAAAIAAAACAAAAABAAQAAAAAAAACAAATCwAAEwsA"
            + "AAQAAAAEAAAAAAAAAADAAADgoEAA////AAAAAAAAAAAAAAAAAAAAAAAAAAAA"
            + "AAAiIhERAAAAAAAAAAAAAAIiIiIREREQAAAAAAAAAAAiIiIiEREREQAAAAAA"
            + "AAAiIiIiIhERERERAAAAAAACIiIiIiIRERERERAAAAAAIiIiIiIiERERERER"
            + "AAAAACIiIiIiIhEREREREQAAAAIiIiIiIiIREREREREQAAAiIiIiIiIiERER"
            + "EREREQAAIiIiIiIiIhEREREREREAACIiIiIiIiIRERERERERAAIiIiIiIiIi"
            + "ERERERERERACIiIiIiIiIhEREREREREQAiIiIiIiIiIREREREREREAIiIiIi"
            + "IiIiERERERERERACIiIiIiIiIhEREREREREQAiIiIiIiIiIREREREREREAIi"
            + "IiIiIiIiERERERERERACIiIiIiIiIhEREREREREQACIiIiIiIiIRERERERER"
            + "AAAiIiIiIiIiEREREREREQAAIiIiIiIiIhEREREREREAAAIiIiIiIiIRERER"
            + "EREQAAAAIiIiIiIiERERERERAAAAACIiIiIiIhEREREREQAAAAACIiIiIiIR"
            + "ERERERAAAAAAACIiIiIiEREREREAAAAAAAAAIiIiIhEREREAAAAAAAAAAAIi"
            + "IiIREREQAAAAAAAAAAAAACIiEREAAAAAAAAAAAAAAAAAAAAAAAAAAAAA");

    static final byte[] IMAGE_4BIT_GAP1A = Base64.getMimeDecoder().decode(
            "Qk1uAgAAAAAAAG4AAAAoAAAAIAAAACAAAAABAAQAAAAAAAACAAATCwAAEwsA"
            + "AAQAAAAEAAAAAAAAAADAAADgoEAA////AKqqqqqqqqqqqqqqqqqqqqqqqqqq"
            + "qqqqqqqqqqqqqqqqqqqqqqqqqqoAAAAAAAAAAAAAAAAAAAAAAAAAAAAAIiIR"
            + "EQAAAAAAAAAAAAACIiIiEREREAAAAAAAAAAAIiIiIhEREREAAAAAAAAAIiIi"
            + "IiIREREREQAAAAAAAiIiIiIiEREREREQAAAAACIiIiIiIhEREREREQAAAAAi"
            + "IiIiIiIREREREREAAAACIiIiIiIiEREREREREAAAIiIiIiIiIhEREREREREA"
            + "ACIiIiIiIiIRERERERERAAAiIiIiIiIiEREREREREQACIiIiIiIiIhERERER"
            + "EREQAiIiIiIiIiIREREREREREAIiIiIiIiIiERERERERERACIiIiIiIiIhER"
            + "EREREREQAiIiIiIiIiIREREREREREAIiIiIiIiIiERERERERERACIiIiIiIi"
            + "IhEREREREREQAiIiIiIiIiIREREREREREAAiIiIiIiIiEREREREREQAAIiIi"
            + "IiIiIhEREREREREAACIiIiIiIiIRERERERERAAACIiIiIiIiEREREREREAAA"
            + "ACIiIiIiIhEREREREQAAAAAiIiIiIiIREREREREAAAAAAiIiIiIiEREREREQ"
            + "AAAAAAAiIiIiIhERERERAAAAAAAAACIiIiIRERERAAAAAAAAAAACIiIiERER"
            + "EAAAAAAAAAAAAAAiIhERAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA==");

    static final byte[] IMAGE_4BIT_GAP1B = Base64.getMimeDecoder().decode(
            "Qk16AgAAAAAAAHoAAAAoAAAAIAAAACAAAAABAAQAAAAAAAACAAATCwAAEwsA"
            + "AAQAAAAEAAAAAAAAAADAAADgoEAA////AKqqqqqqqqqqqqqqqqqqqqqqqqqq"
            + "qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqoAAAAAAAAAAAAAAAAA"
            + "AAAAAAAAAAAAIiIREQAAAAAAAAAAAAACIiIiEREREAAAAAAAAAAAIiIiIhER"
            + "EREAAAAAAAAAIiIiIiIREREREQAAAAAAAiIiIiIiEREREREQAAAAACIiIiIi"
            + "IhEREREREQAAAAAiIiIiIiIREREREREAAAACIiIiIiIiEREREREREAAAIiIi"
            + "IiIiIhEREREREREAACIiIiIiIiIRERERERERAAAiIiIiIiIiEREREREREQAC"
            + "IiIiIiIiIhEREREREREQAiIiIiIiIiIREREREREREAIiIiIiIiIiERERERER"
            + "ERACIiIiIiIiIhEREREREREQAiIiIiIiIiIREREREREREAIiIiIiIiIiERER"
            + "ERERERACIiIiIiIiIhEREREREREQAiIiIiIiIiIREREREREREAAiIiIiIiIi"
            + "EREREREREQAAIiIiIiIiIhEREREREREAACIiIiIiIiIRERERERERAAACIiIi"
            + "IiIiEREREREREAAAACIiIiIiIhEREREREQAAAAAiIiIiIiIREREREREAAAAA"
            + "AiIiIiIiEREREREQAAAAAAAiIiIiIhERERERAAAAAAAAACIiIiIRERERAAAA"
            + "AAAAAAACIiIiEREREAAAAAAAAAAAAAAiIhERAAAAAAAAAAAAAAAAAAAAAAAA"
            + "AAAAAA==");

}
---"IndexedBMPReadTest.java"--

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