For change picture dpi

Question

1.00/5 (1 vote)

See more:

how can i change picture dpi from 96 dpi to 300 dpi i c#

What I have tried:

private void button2_Click(object sender, EventArgs e)
{
var filename = @"--input--image--";
var targetfile = @"--output-image--";

using (var image = Image.FromFile(filename))
{
// changing to 96 DPI
var resolution = new byte[8] { 0, 0, 96, 0, 0, 0, 1, 0 };

if (image.PropertyIdList.Contains(282))
{
var xResolution = image.GetPropertyItem(300);
xResolution.Value = resolution;
image.SetPropertyItem(xResolution);
}
if (image.PropertyIdList.Contains(283))
{
var yResolution = image.GetPropertyItem(300);
yResolution.Value = resolution;
image.SetPropertyItem(yResolution);
}

image.Save(targetfile, image.RawFormat);
}
}
but this is not working

Posted 6-Sep-16 0:08am

Member 12722563

Updated 6-Sep-16 0:22am

Add a Solution

Comments

Philippe Mori 6-Sep-16 13:24pm

Is it that hard to use a code block to make code readable? I am not interested in answering such questions as it take twice as much time to understand unformatted code...

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

OriginalGriff · Answer 1 · 2016-09-06T00:22:00

Changing resolution is complicated: it's not just a case of altering a simple variable.
You need to look at how images are stored: they contain a fixed number of pixels (x width by y height) and the DPI value only controls how many of those are initially displayed in a physical inch on a particular device when the image is drawn to it. Changing the DPI values in the file doesn't change the number of pixels, and often won't affect how the image is displayed, given that it's frequently stretched or shrunk to fit into a particular part of a display or page.

It's possible to "upscale" or "downscale" the resolution by re-rendering the image, but that doesn't add detail (despite what you see on TV) - it just makes pixels bigger or extrapolates extra pixel values when you upscale, or discards details when you downscale. Even then, it's not a trivial process.

And reading and saving files is a bad idea unless you really, really need to - most images are compressed, and the most popular format - jpeg - uses a "lossy" compression, so each time you save the image, you lose data which you cannot recover. Often 4 or 5 saves is enough to reduce a file to unusability, but even one extra can "soften" detail out noticeably.