How to detect if a jpeg contains cmyk color profile?

Question

I have some code that scales the images users upload. It works perfectly in most situations, but sometimes they upload jpegs that contain cmyk information.

After googling a bit, it seems like jpegs with cmyk values isn't valid, but since they work in windows, the users assume it's a problem with my application, so I need to be able to handle those situations. The questions:

How do I detect if the jpeg contains cmyk information?(it would allow me to inform the user why it doesn't work).

How can I convert it to a normal jpeg?

Answer 1

Jpeg is an standard which support any number of planes encoded (they are compressed independently of each other) inside a bitstream, so a jpeg with a cmyk profile is perfectly valid. Most jpeg files are encoded using a jfif container (http://en.wikipedia.org/wiki/JFIF) which originally only supported grayscale images, YCbCr, or sRGB, but it is extensible and Adobe have a custom tag to support cmyk profiles.

Take a look at this link for a workaround http://www.jroller.com/greenhorn/entry/adobe_photoshop_and_jpeg_cmyk, it is in java but you can port it easily to c#.

Answer 2

In ASP.NET you can determine if a JPG is saved using the CMYK profile with the help of the System.Drawing.Imaging.ImageFlags enumeration,

http://msdn.microsoft.com/en-us/library/system.drawing.imaging.imageflags(VS.80).aspx

Let's say you have a basic aspx page where a user uploads a file and you need to tell,

1) is it a jpg? 2) is it using RGB?

Your aspx might be along the lines of,

<form id="form1" runat="server" enctype="multipart/form-data">
<asp:FileUpload ID="myUpload" runat="server" />
<asp:Button ID="submitButton" runat="server" Text="Submit" OnClick="Click_submitButton" />      
<br /><br />     
<asp:Literal ID="feedback" runat="server" />
</form>

and then for your code behind (C#) you can do,

using System;
using System.Collections.Generic;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class _Default : System.Web.UI.Page 
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }

    protected void Click_submitButton(object sender, EventArgs e)
    {
        if (myUpload.HasFile && isUploadAJpeg(myUpload.PostedFile))
        {
            System.Drawing.Bitmap uploadedImage = new System.Drawing.Bitmap(myUpload.PostedFile.InputStream);
            if (isFileACMYKJpeg(uploadedImage))
            {
                feedback.Text = "The file is a CYMK jpg";
            }
            else
            {
                feedback.Text = "This is a RGB jpg";
                //it is a rgb jpg --> do something with it
            }
        }
        else
        {
            feedback.Text = "You did not upload a jpg";
        }
    }

    protected bool isUploadAJpeg(HttpPostedFile someFile)
    {
        if (someFile.ContentType == "image/jpg" || someFile.ContentType == "image/jpeg" || someFile.ContentType == "image/pjpeg")
        {
            return true;
        }
        return false;
    }

    protected bool isFileACMYKJpeg(System.Drawing.Image someImage)
    {
        System.Drawing.Imaging.ImageFlags flagValues = (System.Drawing.Imaging.ImageFlags)Enum.Parse(typeof(System.Drawing.Imaging.ImageFlags), someImage.Flags.ToString());
        if (flagValues.ToString().ToLower().IndexOf("ycck") == -1)
        {
            return false;
        }
        return true;
    }
}

Hope that helps!