Array of bytes[] has no values when is converted from int[]-CodePudding

I'm passing int[] array that hold image, later I want to convert it to bytes[] and save the image to local path. However, I notice that the bytePic[] length is equal to int[] arrPic just the values are missing. There is a screenshot below: arrPic bytePic

Below is the entire function:

public string ChangeMaterialPicture(int[] arrPic, int materialId,string defaultPath)
{
    var material = _warehouseRepository.GetMaterialById(materialId);
    if(material is not null)
    {
        // Convert the Array to Bytes

        byte[] bytePic = new byte[arrPic.Length];
        for(var i = 0; i < arrPic.Length; i  )
        {
            AddByteToArray(bytePic, Convert.ToByte(arrPic[i]));
        }
        // Convert the  Bytes to IMG
        string filename = Guid.NewGuid().ToString()   "_.png";
        System.IO.File.WriteAllBytes(@$"{defaultPath}\materials\{material.VendorId}\{filename}", bytePic);

        // Update the Image
        material.Picture = filename;
        _warehouseRepository.UpdateMaterial(material);

        return material.Picture;
    }
    else
    {
        return String.Empty;
    }
}

public byte[] AddByteToArray(byte[] bArray, byte newByte)
{
    byte[] newArray = new byte[bArray.Length   1];
    bArray.CopyTo(newArray, 1);
    newArray[0] = newByte;
    return newArray;
}

CodePudding user response：

You are creating the new array newArray in AddByteToArray and return it. But at the call site you are never using this returned value and the bytePic array remains unchanged.

The code in AddByteToArray makes no sense. Why create a new array when the intention was to insert one byte into an existing array? What you need to do is to cast the int into byte. Simply write:

byte[] bytePic = new byte[arrPic.Length];
for (int i = 0; i < arrPic.Length; i  )
{
    bytePic[i] = (byte)arrPic[i];
}

And delete the method AddByteToArray.

This assumes that every value in the int array is in the range 0 to 255 and therefore fits into one byte.

There are different ways to do this. With LINQ you could also write:

byte[] bytePic = arrPic.Select(i => (byte)i).ToArray();

CodePudding user response：

I would assume your original array uses a int to represent a full RGBA-pixel, since 32bit per pixel mono images are very rare in my experience. And if you do have such an image, you probably want to be more intelligent in how you do this conversion. The only time just casting int to bytes would be a good idea is if you are sure only the lower 8 bits are used, but if that is the case, why are you using an int-array in the first place.

If you actually have RGBA-pixles you do not want to convert individual int-values to bytes, but rather convert a single int value to 4 bytes. And this is not that difficult to do, you just need to use the right methods. The old school options is to use Buffer.BlockCopy.

Example:

byte[] bytePic = new byte[arrPic.Length * 4];
Buffer.BlockCopy(arrPic, 0, bytePic, 0, bytePic.Length);

But if your write-method accepts a span you might want to just convert your array to a span and cast this to the right type, avoiding the copy.