the size of the image increases after applying steganography technique

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i have problem with my image steganography code as it increases the size of the image after embeding the text.....for example if i load 10 kb pic as a input and embed 1 kb of text file then the resultent file size will be 150 kb aprox....thanks in advance

what is wrong with this piece of code???

C#

public static Bitmap embedText(string text, Bitmap bmp)
{
    State s = State.hiding;

    int charIndex = 0;
    int charValue = 0;
    long colorUnitIndex = 0;

    int zeros = 0;

    int R = 0, G = 0, B = 0;

    for (int i = 0; i < bmp.Height; i++)
    {
        for (int j = 0; j < bmp.Width; j++)
        {
            Color pixel = bmp.GetPixel(j, i);

            pixel = Color.FromArgb(pixel.R - pixel.R % 2,
                pixel.G - pixel.G % 2, pixel.B - pixel.B % 2);

            R = pixel.R; G = pixel.G; B = pixel.B;

            for (int n = 0; n < 3; n++)
            {
                if (colorUnitIndex % 8 == 0)
                {
                    if (zeros == 8)
                    {
                        if ((colorUnitIndex - 1) % 3 < 2)
                        {
                            bmp.SetPixel(j, i, Color.FromArgb(R, G, B));
                        }

                        return bmp;
                    }

                    if (charIndex >= text.Length)
                    {
                        s = State.filling_with_zeros;
                    }
                    else
                    {
                        charValue = text[charIndex++];
                    }
                }

                switch (colorUnitIndex % 3)
                {
                    case 0:
                        {
                            if (s == State.hiding)
                            {
                                R += charValue % 2;

                                charValue /= 2;
                            }
                        } break;
                    case 1:
                        {
                            if (s == State.hiding)
                            {
                                G += charValue % 2;

                                charValue /= 2;
                            }
                        } break;
                    case 2:
                        {
                            if (s == State.hiding)
                            {
                                B += charValue % 2;

                                charValue /= 2;
                            }

                            bmp.SetPixel(j, i, Color.FromArgb(R, G, B));
                        } break;
                }

                colorUnitIndex++;

                if (s == State.filling_with_zeros)
                {
                    zeros++;
                }
            }
        }
    }

    return bmp;
}

[edit]Code block added - OriginalGriff[/edit]

Posted 17-Jan-14 18:15pm

Adi5555

Updated 17-Jan-14 21:08pm

OriginalGriff

v2

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BillWoodruff 18-Jan-14 2:17am

Do you know for certain that the increase in file size is not what you should expect given the relative sizes of the source graphic file and the text to be hidden in it ?

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OriginalGriff · Answer 1 · 2014-01-17T21:12:00

Solution 1

Best guess?
You are loading a JPG file, and saving it as a bitmap...

A 10K bitmap is not big: it's roughly 50x50 pixels, so storing 1K of text into it isn't going to work too well anyway!

Posted 17-Jan-14 21:12pm

OriginalGriff

Comments

Adi5555 18-Jan-14 4:29am

no it takes all types of image and save them in .png extention

OriginalGriff 18-Jan-14 5:08am

PNG is a compressed format, but...it depends on the data how much compression you get because it is not a "lossy" format like JPG. So if you feed it a 10K JPG, add 1K text, and save as a PNG, then there is a very, very good chance that you will end up with a much bigger file!

Adi5555 19-Jan-14 8:12am

Thanks ! i understand what u said ..... i wana know what should i do to maintain the size of the image after hiding data ???

OriginalGriff 19-Jan-14 8:24am

The only way to do that is to use an uncompressed format: bitmap for example.
Input a bitmap : output a bitmap and they will be the same size.
Input a compressed format : output any format and it's unlikely they will be the same (or they will throw away some if not all of your hidden data when it is compressed)

Adi5555 19-Jan-14 8:31am

but i have heard bitmap is not a good format security wise...is that true ??

OriginalGriff 19-Jan-14 8:57am

Let's be honest: none of this is "secure", it's all pretty transparent if you are looking for it regardless of the file format - so if you want security you need to look at much better methods than this!
The problem is that either you use an uncompressed format (such as bitmap, but they are all pretty much the same) and then you can't see the file size has changed, or you use a lossless compressed format such as PNG where the file size varies according to the data content - so when you change the data by "hiding" info in it, you will almost always end up with a different size file. Or, you could use a lossy compression format such as JPG, but then it will almost certainly corrupt your "hidden" data.

This is the way of things, I'm afraid!

Adi5555 19-Jan-14 11:21am

some people says that the file size will not increase after hiding data ....i havnt seen a single software like that....so is it impossible to retain the size of original image after hiding data ??

OriginalGriff 19-Jan-14 11:48am

No - but you have to use a format that doesn't involve compression. Like Bitmap for example...

Adi5555 20-Jan-14 2:19am

do u mean takes input as bitmap and give output as a bitmap ??

BillWoodruff · Answer 2 · 2014-01-18T00:31:00

The code used here is on a Romanian web site which seems to be accessible now only via the Google cached page: [^].

The same code is used on this web-site: [^], where the code shows a claim to Copyright by "Rajesh G." The code there also demonstrates the use of encryption and decryption of the Text used.

The OP here also has the same question on StackOverFlow: [^].

We have no direct evidence here that tells us what type of image file the OP is loading before applying the steganographic transformation. We don't know how many bits-per-pixel there are in the image file source, or how many bits-per-pixel are used in saving the transformed image. The code, obviously, shows we are dealing with at least 24 bpp (one byte each R G B). Seems reasonable to assume the image is being saved as a 24 bpp .png file (no indication the alpha channel is being used).

A cursory examination of the code suggests the processing is not adding any bytes/pixels to the image.

imho, the principle of Occam's Razor modulo "reasonable doubt" suggests we don't have enough information to make a reasonable guess, but I don't work for the NSA :)