Develop Reference

How can I get image content as pixel and create image from it in ASP.NET Core 6 Web API?

I try to save my images on my server, but I can't let my server save file and virus because of that I want to get image content as pixels of rgb and after that I create image by myself.
I can't use bitmap (or other type in C# like bitmapImage, ... etc) and I don't know how I can do this with sixlabors.ImageSharp.
I have some code that I tried but I can't implement the exact logic that I want (code shown here):
[HttpPost("[action]")]
public async Task<IActionResult> Get([FromForm] ImageFormat file)
{
await using var memoryStream = new MemoryStream();
await file.File.CopyToAsync(memoryStream);
IImageFormat format;
using (var image = Image.Load(memoryStream.ToArray(), out format))
{
using (var output = new MemoryStream())
{
image.Save(output, format);
var responseType = format.Name.ToLower();
return File(output.ToArray(), "application/octet-stream", file.File.FileName);
}
}
return null;
}
Can anybody help me with this problem?

i don't see a reason to convert image into image: there are several format zip-algorythms etc.wich you have to support in that case. example jpg is not bitmap, there is convertion issue - quality of image becomes less each conversion time. Image itself is not executable - it can be used only as container for virus body, can't harm your OSystem itself, another executable part should works somewhere.
But even if you would like to store images on disk, in other format - you can convert image to base64 text (one line of code, like example) - it less harmful and well known way to work with any file type. you can zip image by cszip, you can change file name and extension to hide file type.
I don't see a reasson to convert one image to another for this scenario/task.

How do I create/edit a PNG file in C#?

I've written a program that can create digital art. Images like the Mandelbrot Set and the Julia Set. But I'm looking to save these images as PNGs. At present, in Java, I'm generating the images in an application window and then taking a screen shot of the display. However, I lose the finer detail of these images. Plus, this method also reduces the physical size of the images as well. I want to potentially be able to make a big poster out of these pictures.
In C#, I'm using the following:
Bitmap myimage = new Bitmap("image.png"); and: myimage.SetPixel(x,y, Color.FromArgb(255*colors[x,y], 255*colors[x,y], 255*colors[x,y]); where colors[,] is some value between 0 and 1.
The code runs fine, minus the Bitmap declaration. My understanding is that new Bitmap(filepath); allows you to edit and manipulate the PNG image. Am I right to think that? How do I create/edit a PNG file in C#?
(edit)PS: The PNG file, "image.png", does exist in the solution folder.

Firstly you have to know the step by step process in creating the PNG file.
Setup Aspose.Imaging for .NET package from Nuget.org.
Include reference to following two namespaces: Aspose.Imaging,
Aspose.Imaging.ImageOptions.
Specify license using SetLicense method before converting.
Read BMP file into an Image object.
Set attributes for output PNG image using PngOptions class.
Save the output PNG image with the specified PNG options.
Code to create PNG image from BMP
using System;
//Use following namespaces to create PNG image
using Aspose.Imaging;
using Aspose.Imaging.ImageOptions;
namespace CreatePNGImage
{
class Program
{
static void Main(string[] args)
{
//Set license before creating PNG image from BMP
Aspose.Imaging.License AsposeImagingLicense = new Aspose.Imaging.License();
AsposeImagingLicense.SetLicense(#"c:\asposelicense\license.lic");
//load input BMP image
Image BmpToPngImage = Image.Load("InputBMPImage.bmp");
//set attributes of the output PNG file
PngOptions PNGImageOptions = new PngOptions();
PNGImageOptions.ResolutionSettings = new ResolutionSetting(300, 300);
PNGImageOptions.CompressionLevel = 6;
//save converted output PNG image
BmpToPngImage.Save("OutputPNGImage.png", PNGImageOptions);
}
}
}
Try this to create the PNG file out of c#.

Set image resolution

I have array of image bytes and I would like to set resolution. Original image can be JPEG, PNG, BMP. Output - PNG. I am using ImageMagic to convert image and do some manipulations.
using (var image = this.Convert(originalImage, height, width))
using (var stream = new MemoryStream())
{
image.Quality = 90;
image.Write(stream, MagickFormat.Png);
return stream.GetBuffer();
}
I tryed to modify image.GetExifProfile, but has no success (at least for PNG images).
I can't use any comandline tool (like ImageMagic or ExifTool) here.
There are 3 exiff tags I need to modify
XResolution
YResolution
ResolutionUnit
I can successfully achieve this with bitmap, but it also resource overhead (need to create MemoryStream ...).
I have found some Pdf specification, but it will consume time to make it all work.
Does any can point me to right direction?
Thanks.

C# get width/height of image on web without downloading whole file?

I believe with JPGs, the width and height information is stored within the first few bytes. What's the easiest way to get this information given an absolute URI?

First, you can request the first hundred bytes of an image using the Range header.
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url);
request.Headers.Set(HttpRequestHeader.UserAgent, "Range: bytes=0-100");
Next, you need to decode. The unix file command has a table of common formats, and the locations of key information. I'd suggest installing Cygwin and taking a look at /usr/share/file/magic.
For gif's and png's, you can easily get the image dimensions from the first 32 bytes. However, for JPEGs, #Andrew is correct in that you can't reliably get this information. You can figure out if it has a thumbnail, and the size of the thumbnail.
The get the actual jpeg size, you need to scan for the start of frame tag. Unfortunately, one can't reliably determine where this is going to be in advance, and a thumbnail could push it several thousand bytes into the file.
I'd recommend using the range request to get the first 32 bytes. This will let you determine the file type. After which, if it's a JPEG, then download the whole file, and use a library to get the size information.

I am a bit rusty at this, but with jpeg, it might not be as simple as it seems. Jpeg has a header within each segment of data which has its own height / width and resolution. jpeg was not designed to be streamed easily. You might need to read the entire image to find the width and height of each segment within the jpeg to get the entire width and height.
If you absolutely need to stream an image consider changing to another format which is easier to stream, jpeg is going to be tough.
You could do it if you can develop a server side program that would seek forward and read the header of each segment to compute the width and height of the segment.

It's a bit Heath Robinson, but since browsers seem to be able to do it perhaps you could automate IE to download the image within a webpage and then interrogate the browser's DOM to reveal the dimensions before the image has finished downloading?

Use this code:
public static async Task<Size> GetUrlImageSizeAsync(string url)
{
try
{
var request = WebRequest.Create(url);
request.Headers.Set(HttpRequestHeader.UserAgent, "Range: bytes=0-32");
var size = new Size();
using (var response = await request.GetResponseAsync())
{
var ms = new MemoryStream();
var stream = response.GetResponseStream();
stream.CopyTo(ms);
var img = Image.FromStream(ms);
size = img.Size;
}
return size;
}
catch
{
return new Size();
}
}

Can't convert image to bytes[] C#

I'm very new to this stuff of saving images to the DB, and even when I thought it was very straight forward, it wasn't. What I'm trying to do is read and image file from the same computer in any format, display it in a picture box, and then convert the image to bytes to save it in the DB. Until now, I can display the image in the picture box, but I can't convert the image to bytes. Here's my code:
private void DisplayImage()
{
if (openFileDialog.ShowDialog(this) == DialogResult.OK)
{
try
{
Stream file;
if ((archivo = openFileDialog.OpenFile()) != null)
{
using (file)
{
pictureBox.Image = Image.FromStream(file);
}
}
}
catch (Exception ex)
{
...
}
}
}
That's a simple method that just displays the image in the picture box. The real problem is with the following method:
public static byte[] ConvertImageToBytes(Image image)
{
if (image != null)
{
MemoryStream ms = new MemoryStream();
using (ms)
{
image.Save(ms, ImageFormat.Bmp);
byte[] bytes = ms.ToArray();
return bytes;
}
}
else
{
return null;
}
}
When it tries to save the image to the memory stream, I get the error:
System.Runtime.InteropServices.ExternalException: A generic error occurred in GDI+.
Any ideas on what's happening?

You should use the RawFormat property of the original image as a parameter to the Save method, not default to a Bitmap. This will avoid image format type errors. eg:
image.Save(ms, image.RawFormat);
ms.Position = 0;
byte [] bytes=ms.ToArray();
I'd advise actually saving images to the file-system and simply storing the file path (preferably relative) in the database.
BLOBs (ie images etc) in a database cannot be indexed, are often stored in a secondary, slower access database area and will quickly blow out the size of the database (slower backups etc).

Cant you simply Read the file and load it to a byte[] using the File class:
byte[] imgData = System.IO.File.ReadAllBytes(#"C:\My Pic\Myfile.jpg");
You can pick the image path from your Open Dialog box.

That particular exception generally means that you are trying to save the image as the wrong format. In your code you specify ImageFormat.Bmp - is it actually a bitmap image, or did you perhaps load it from a JPEG or PNG? Attempting to save as a different format from the one you loaded will fail with ExternalException, as specified in the documentation.
Incidentally, I don't recommend storing images in a database and I believe most people here will agree. Databases may be able to handle this task but they are not optimized for it, and you end up hurting the performance of both your database and your application. Unless you are using SQL Server 2008 FILESTREAM columns, it is more efficient to store images on the file system.

It may be stupid to answer my own question, but I just found out that if I want to convert the Image object to bytes, I have to leave the original stream open. I saw this issue in another page I can't quite remember, and I tested it by leaving the stream open and it's true. So the format wasn't the problem. But I will take the advice of all of you and store the images in a separate directory. Thanks for your help guys!

The problem with this is that stream must be open during the lifetime of of the image otherwise will fail.
One solution that worked for me is just to create a copy of the image like this:
using (var ms = new MemoryStream(bytes))
{
_image = new Bitmap(Image.FromStream(ms));
}