CODEWITHSUNDEEP
vb.netimageurl
user3102516
user3102516

Reputation: 97

Retrieve image dimensions from URL

I'm trying to retrieve image dimensions from an image URL. How is this possible? I've done plenty of research and haven't found any code that can achieve this, all of the information gets image dimensions from an image on the local disk which is not what I want.

Is it possible to achieve this?

Upvotes: 3

Views: 1226

Answers (2)

srka
srka

Reputation: 802

You don't need to download entire file, only first few bytes. If image is PNG, width is in 17th, 18th, 19th and 20th byte, and height is in 21st, 22nd, 23rd and 24th byte. If it's GIF, width is in 7th and 8th byte, and height is in 9th and 10th byte. It's complicated for JPG. Note that byte order in PNG is big-endian(255 - 000000FF) and in GIF is little-endian(255 - FF00). Here is code:

Imports System
Imports System.Net
Imports System.IO
Imports System.Text
Imports System.Threading
Imports Microsoft.VisualBasic

Public Class Form1

    Private Sub GetImageDimensions() Handles Button1.Click
        HTTPWebRequest_GetResponse.Main("http://www.example.com/image.png") 'without slash at end
        Do
            If HTTPWebRequest_GetResponse.done = True Then
                Dim width As Integer = HTTPWebRequest_GetResponse.width
                Dim height As Integer = HTTPWebRequest_GetResponse.height
                Exit Do
            End If
            If HTTPWebRequest_GetResponse.exception Then
                Exit Do 'prevents inifinite loop if exception occured
            End If
        Loop

    End Sub


End Class

Public Class RequestState
    ' This class stores the State of the request. 
    Public requestData As StringBuilder
    Public BufferRead() As Byte
    Public request As HttpWebRequest
    Public response As HttpWebResponse
    Public streamResponse As Stream

    Public Sub New()
        requestData = New StringBuilder("")
        request = Nothing
        streamResponse = Nothing
    End Sub 'New 
End Class 'RequestState


Class HTTPWebRequest_GetResponse

    Private BUFFER_SIZE As Integer = 1024
    Public Shared response As String
    Public Shared done As Boolean = False
    Public Shared length As Long = 1
    Public Shared progress As Integer
    Public Shared myHttpWebRequest As HttpWebRequest
    Public Shared myRequestState As New RequestState
    Public Shared status As String
    Private Shared body As Boolean = False
    Public Shared responseStream As Stream
    Private Shared offset As Integer
    Private Shared bytestoread As Integer
    Public Shared width As Integer
    Public Shared height As Integer
    Private Shared imageType As String
    Public Shared exception As Boolean = False

    Shared Sub Main(url As String)
        done = False
        exception = False
        Try
            If url.Substring(url.Length - 4) = ".png" Then
                myRequestState.BufferRead = New Byte(23) {}
                offset = 16
                bytestoread = 24
                imageType = "png"
            ElseIf url.Substring(url.Length - 4) = ".gif" Then
                myRequestState.BufferRead = New Byte(9) {}
                offset = 6
                bytestoread = 10
                imageType = "gif"
            Else
                Throw New NotSupportedException("You can only use this with PNG or GIF images.")
            End If


            ' Create a HttpWebrequest object to the desired URL.  
            myHttpWebRequest = WebRequest.Create(url)

            ' Create an instance of the RequestState and assign the previous myHttpWebRequest 
            ' object to its request field.   

            myRequestState.request = myHttpWebRequest

            ' Start the asynchronous request. 
            Dim result As IAsyncResult = CType(myHttpWebRequest.BeginGetResponse(New AsyncCallback(AddressOf RespCallback), myRequestState), IAsyncResult)
        Catch e As WebException
            exception = True
            Debug.WriteLine(ControlChars.Lf + "Main Exception raised!")
            Debug.WriteLine(ControlChars.Lf + "Message: " + e.Message)
            Debug.WriteLine(ControlChars.Lf + "Status: " + e.Status)
        Catch e As Exception
            exception = True
            Debug.WriteLine(ControlChars.Lf + "Main Exception raised!")
            Debug.WriteLine("Source : " + e.Source)
            Debug.WriteLine("Message : " + e.Message)
        End Try
    End Sub 'Main

    Private Shared Sub RespCallback(asynchronousResult As IAsyncResult)
        Try
            Dim myHttpWebRequest As HttpWebRequest = myRequestState.request
            myRequestState.response = CType(myHttpWebRequest.EndGetResponse(asynchronousResult), HttpWebResponse)

            ' Read the response into a Stream object. 
            Dim responseStream As Stream = myRequestState.response.GetResponseStream()
            myRequestState.streamResponse = responseStream

            ' Begin the Reading of the contents of the HTML page. 

            responseStream.Read(myRequestState.BufferRead, 0, bytestoread)
            If BitConverter.IsLittleEndian Then
                If imageType = "png" Then
                    height = BitConverter.ToInt32(myRequestState.BufferRead.Skip(offset).Reverse.Take(4).ToArray, 0)
                    width = BitConverter.ToInt32(myRequestState.BufferRead.Skip(offset).Reverse.Skip(4).Take(4).ToArray, 0)
                Else
                    width = BitConverter.ToInt16(myRequestState.BufferRead.Skip(offset).Skip(6).Take(2).ToArray, 0)
                    height = BitConverter.ToInt16(myRequestState.BufferRead.Skip(offset).Skip(8).Take(2).ToArray, 0)
                End If
            Else
                If imageType = "png" Then
                    width = BitConverter.ToInt32(myRequestState.BufferRead.Skip(offset).Skip(16).Take(4).ToArray, 0)
                    height = BitConverter.ToInt32(myRequestState.BufferRead.Skip(offset).Skip(20).Take(4).ToArray, 0)
                Else
                    height = BitConverter.ToInt16(myRequestState.BufferRead.Skip(offset).Reverse.Take(2).ToArray, 0)
                    width = BitConverter.ToInt16(myRequestState.BufferRead.Skip(offset).Reverse.Skip(2).Take(2).ToArray, 0)
                End If
            End If
            done = True
            Return
        Catch e As WebException
            exception = True
            Debug.WriteLine(ControlChars.Lf + "RespCallback Exception raised!")
            Debug.WriteLine(ControlChars.Lf + "Message: " + e.Message)
            Debug.WriteLine(ControlChars.Lf + "Status: " + e.Status)
        Catch ex As Exception
            exception = True
            Debug.WriteLine(ControlChars.Lf + "RespCallback Exception raised!")
            Debug.WriteLine(ex.ToString)
        End Try
    End Sub 'RespCallback
End Class

Code is large, but I think this is only to download only enough bytes.

Sources: https://en.wikipedia.org/wiki/Gif#Example_GIF_file https://en.wikipedia.org/wiki/Portable_Network_Graphics#Technical_details http://www.libpng.org/pub/png/spec/1.2/PNG-Chunks.html#C.IHDR

Upvotes: 5

chris_techno25
chris_techno25

Reputation: 2477

I don't think this is possible. Thing is...before any information can be retrieved from a certain URL or file or picture from the internet, it has to be downloaded first. It's the reason why Windows has the temp folder. Everything is stored inside the temp folder including the scenario where you're just browsing the internet. So my suggestion would be to do the same thing, download the picture first and save it somewhere and retrieve the information you want, then you can delete the file after if you don't want it anymore.

Upvotes: 0

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