Detect absence of light in Android camera

Question

I need to capture the image of the Android camera and detect if the user puts his finger on top (dark). Is there a library that does it simply?

Thank you,

Answer 1

I’ve never heard of such a library, I believe only by performing a direct check on the captured image to find out. And performing this check "manually" is not so difficult if it doesn’t depend on a lot of precision.

For example I would do something like this:

    public static boolean ImagemEscura(Bitmap img)
    {
        float totalpixel = img.getWidth() * img.getHeight();
        float totalpixelescuro = 0;
        for(int x = 0; x < img.getWidth(); x++)
        {
            for(int y = 0; y < img.getHeight(); y++)
            {
                int cor = img.getPixel(x, y);
                //supondo que o valor como sendo escuro significa que a soma dos
                //valores RGB não podem ultrapassar 90
                if(SomaRGB(cor) > 90)
                {
                    totalpixelescuro++;
                }
            }
        }       
        //se existir mais de 75% dos pixels escuro ele entende que o dedo esta na frente
        return totalpixelescuro/totalpixel > 0.75f;
    }

    public static int SomaRGB(int cor)
    {
        return getRed(cor) + getGreen(cor) + getBlue(cor);
    }

    public static int getRed(int argb) 
    {
        return argb >> 16 & 0xFF;
    }

    public static int getGreen(int argb)
    {
        return argb >> 8 & 0xFF;
    }

    public static int getBlue(int argb)
    {
        return argb & 0xFF;
    }

You may need to put it to run on a Thread outside the UI to avoid some crash in the App and make some adjustments to the parameters to more accurately meet your needs, but I imagine this is already a north for you.