how to increase dpi with opencv?

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I need to increase dpi my image before read by ocr with opencv. the problem are :

  1. I dont know my image dpi right now
  2. and I dont know how to increase dpi of the image

i search in google, and almost every answer suggest using resize

cv2.resize()

image = cv2.imread("source.png")
resized_image = cv2.resize(image, (100, 50)) #I need to change it to 300 DPI

resize only to change size of image, but after all not increase dpi in image, because i tried use it, and when i check in photoshop, dpi not changed

show please help me for that 2 questions

how to do it with opencv?

honestly I need to change dpi to 300, why i need to know current dpi? because if it already dpi > 300, so I dont need to convert it.

oya i do it with python


The dpi is just a number in the JPEG/TIFF/PNG header. It is entirely irrelevant to the world and his dog until you print the image and then it determines how large the print will be given the image's dimensions in pixels.

During image processing, it is irrelevant. The only thing of any interest is the number of pixels you have. That is the ultimate determinant of image quality, or information content - however you want to describe it.

I don't believe you can set it with OpenCV. You can certainly set it with ImageMagick like this in the Terminal:

mogrify -set density 300 *.png           # v6 ImageMagick
magick mogrify -set density 300 *.png    # v7 ImageMagick

You can check it with:

identify -format "Density: %x x %y" SomeImage.jpg    # v6 ImageMagick
magick identify -format ... as above                 # v7 ImageMagick

You can do similar things with exiftool in Terminal - note that exiftool is MUCH smaller and easier to maintain than ImageMagick because it is "just" a (very capable) single Perl script:

Extract image resolution from EXIF IFD1 information:

exiftool -IFD1:XResolution -IFD1:YResolution image.jpg

Extract all tags with names containing the word "Resolution" from an image|:

exiftool '-*resolution*' image.jpg

Set X/Y Resolution (density) on image.jpg:

exiftool -xresolution=300 -yresolution=300 image.jpg

Here is a little demonstration of what I mean at the beginning of my answer...

Use ImageMagick to create an image 1024x768 with no dpi information:

convert -size 1024x768 xc:black image.jpg

Now examine it:

identify -verbose image.jpg

Image: image.jpg
  Format: JPEG (Joint Photographic Experts Group JFIF format)
  Mime type: image/jpeg
  Class: PseudoClass
  Geometry: 1024x768+0+0
  Units: Undefined
  Colorspace: Gray
  Type: Bilevel
  ...
  ...

Now change the dpi and set the dpi units and examine it again:

mogrify -set density 300 -units pixelsperinch image.jpg   # Change dpi

identify -verbose image.jpg                               # Examine

Image: image.jpg
  Format: JPEG (Joint Photographic Experts Group JFIF format)
  Mime type: image/jpeg
  Class: PseudoClass
  Geometry: 1024x768+0+0            <--- Number of pixels is unchanged
  Resolution: 300x300               <---
  Print size: 3.41333x2.56          <--- Print size is now known
  Units: PixelsPerInch              <---
  Colorspace: Gray
  Type: Bilevel
  ...
  ...

And now you can see that suddenly we know how big a print will come out and that the number of pixels has not changed.

Resolution to 300 dpi - OpenCV Q&A Forum, hi! Is there any method to set the Resolution of Mat type image to 300dpi in OpenCV-3.0 before passing it to Tesseract-OCR for further text  1 Answer 1. For OCR, what really matters is the resolution in pixels. Because the physical characters can range from tiny to huge, independently of the DPI of the acquisition device. As a rule of thumb, stroke width around 3 pixels is a good start.


Increase or decrease DPI of an image, Increase or decrease DPI of an image. Hello guys, I have a pool of jpg files and need to change them for tiff. The point is that some of them are  Re: Increase or decrease DPI of an image On 02.06.2014 22:20, Vinícius Souza [hidden email] [OpenCV] wrote: > I have a pool of jpg files and need to change them for tiff. The point is > that some of them are 96dpi and other are 600dpi.


DPI is inherited property of graphical device - monitor, scanner, camera, etc. For example - lets say that we are scanning image, and we want to get image with better quality - so we set higher DPI value in scanner options. If no better DPI option - so we need to buy a better scanner which supports more scan resolutions. There are devices/methods which are able to achieve 100 000 DPI

OpenCV & Python: How to Change Resolution or Rescale Frame , OpenCV & Python: How to Change Resolution or Rescale Frame Logo} OpenCV makes it Duration: 11:09 Posted: Apr 8, 2018 I'm sorry, I think your question makes no sense. From what I know of opencv types and structures, there is no info for DPI (you can check this in the IplImage header, explained on the html


how to resize image without changing DPI in opencv for detecting , i resized the image using open cv and it changed the dpi of the image from 300 dpi to 90 dpi . What is the correct way to resize image without  Then the output will be shown with some comparisons as well. Requirements: First, you need to setup your Python Environment with OpenCV. Goals: In this tutorial, I will show you how to resize the input image according to the screen resolution. Documentation: Parameters: The specified window size is for the image area.


How can I increase the dpi of an image?, If you don't have Photoshop, you can use free Irfanview to change image DPI. Go to Image -> Resize/Resample in the menu. Now set DPI value on the bottom  OpenCV with Python Series #2 : How to Change Resolution or Rescale Frame Related guide: https://kirr.co/0l6qmh New to OpenCV? Try this: https://youtu.be/YY9f


cv2.resize() - OpenCV Python function to Resize Image, OpenCV Resize image using cv2.resize(). Resizing an image means changing the dimensions of it, be it width alone, height alone or both. Also,  If you don't have Photoshop, you can use free Irfanview to change image DPI. Go to Image -> Resize/Resample in the menu. Now set DPI value on the bottom of dialog. 8 Recommendations