I want to convert several images into polygon shp files using QGis (Quantum GIS 1.6).
I need to do edge detection AND differentiate between several different colors of lines (red, green, yellow and black). I need good edge detection as my images are scanned in at 200 DPI.
I'm open to other suggestions that don't involve QGis. Could I use Photoshop or would Arcgis do a better job of this?
Inkscape has a rather functional vectorizer (Trace Bitmap, IIRC)
http://inkscape.org/doc/tracing/tutorial-tracing.html
Inskscape's native format is SVG (fully vector based). It allows simplifcation of the resulting paths as well. Also, you might use the resulting XML to process automatically.
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I am using the GDAL C++ library to reclassify raster map images and then create an output image of the new data. However when I create the new the new image and open it, the classification values don't seem to have a color defined, so I just get a black image. I can fix this by going into the image properties and setting a color for each of the 10 classification values I'm using, but that is extremely time consuming for the amount of maps and trials I am doing.
My question is, is there a way to set metadata info through the GDAL API to define a color for each classification value? Just the name of the right function would be great, I can figure it out from there.
I have tried this using ArcGIS and QuantumGIS, and both have the same problem. Also the file type I am using is Erdas Imagine (called "HFA" in GDAL).
You can use SetColorTable() method on your raster band. Easiest to do is to fetch one pre-existing raster using GetColorTable(), and pass it to your new raster.
I have extracted the depth map of 2 images and stored them as .tif file
now I would like to use openGL to join these two images depending on their depth
so I want to read the depth for each image from the .tif file and then use that depth to draw the pixel with the higher depth
to make it more clear the depth map are two images like this
link
so say I have the pervious image and I want to join it with this image
link
my question is how to read this depth from the .tif file
Ok, I'll have a go ;-)
I see the images are just grayscale, so if the "depth" information is just the intensity of the pixel, "joining" them may be just a matter of adding the pixels. This is generally referred to as "blending", but I don't know what else you could mean.
So, you need to;
Read the 2 images into memory
For each pixel (assuming both images the same size):
read the intensity from image A[row,col]
read the intensity from image B[row,col]
write max(A[row,col],B[row,col]) to C[row,col]
Save image C - this is your new "joined" image.
Now OpenGL doesn't have any built-in support for loading/saving images, so you'll need to find a 3rd party library, like FreeImage or similar.
So, that's a lot of work. I wonder if you really want an OpenGL solution or are just assuming OpenGL would be good for graphics work. If the algorithm above is really what you want, you could do it in something like C# in a matter of minutes. It has built-in support for loading (some formats) of image file, and accessing pixels using the Bitmap class. And since your created this images yourself, you may not be bound the the TIFF format.
I'll first tell you the problem and then I'll tell you my solution.
Problem: I have a blank white PNG image approximately 900x900 pixels. I want to copy circles 30x30 pixels in size, which are essentially circles with a different colour. There are 8 different circles, and placed on the image depending on data values which I've created elsewhere.
Solution: I've used ImageMagicK, it's suppose to be good for general purpose image editing etc. I created a blank image
Image.outimage("900x900","white");
I upload all other small 30x30 pixel images with 'read' function.
I upload the data and extract vales.
I place the small 'circle' images on the blank one using the composite command.
outimage.composite("some file.png",pixelx,pixely,InCompositeOp);
This all works fine and the images come up the way I want them too.
However its painfully SLOW. It takes 20 seconds to do one image, and I have 1000 of them. Surely there must be a better way to do this. I've seen other researchers simulate images way more complex and way faster. It's quite possible I took the wrong approach. Maybe I sould be 'drawing' circles instead of 'pasting' them or something. I'm quite baffled. Any input is appreciated.
I suspect that you just need some library that is capable of drawing circles on bitmap and saving that bitmap as png.
For example my Graphin library: http://code.google.com/p/graphin/
Or some such. With Graphin you can also draw one PNG on surface of another as in your case.
You did not give any information about the platform you are using (only "C++"), so if you are looking for a platform independent solution, the CImg library might be worth a try.
http://cimg.sourceforge.net/
By the way, did you try drawing the circles using the ImageMagick C++ API Magick++ instead of "composing" them? I cannot believe that it is that slow.
IN: Visual Studio 2010 Ultimate, Windows 7
OUT: Some small ish PNG images that I will use as custom markers in Google Maps.
Language: C++ (or, if I really have to, C#)
Extra: I need to be able to plot the alpha channel (the transparency). I used PNGwriter library on a Linux machine and that didn't offer this feature.
Extra 2: The .exe will run on a server each time a new custom marker is needed. (Markers have different colors and shapes)
Edit: 1. I want to create a new image. 2. I need a library which I can't seem to find via Google yet.
Do you mean you want to convert from one file format to PNG using C++? Or that you want to render to an image and save the resulting image out as a PNG?
Either way, maybe you should take a look at FreeImage http://freeimage.sourceforge.net/features.html which is an open source image parsing/writing library that supports many formats, including PNG.
I created a kluge to do this. I used a common routine for getting the color (GetColor(red,green,blue,transparency)). I printed in two passes. The first pass would print to a 256 gray scale image. GetColor() would return the transparency as a shade of gray. The second pass would print to a 24-bit color image. GetColor would return the RGB color. After the two passes I merged the two bitmaps with the grayscale becoming the alpha channel for the PNG file.
C++ does not have any facilities built in for editing images. You'd need to find a library.
You could always use .NET.
I would suggest the built in System.Drawing namespace, which is available in both flavors - C++ and C#. Assuming you aren't against using Visual C++ Express, you can always take it from there.
Here's a link to the "official" documentation: System.Drawing Namespace
Within which is the System.Drawing.Graphics namespace, which is possibly what you would want to use.
AND here's a link to a nice little tutorial that will teach you how to import an image and draw on it (or possibly even draw it onto a bitmap): The Wonders of System.Drawing.Graphics
Boost.GIL can work with PNG.
Does anyone know of a c++ library for taking an image and performing image recognition on it such that it can find letters based on a given font and/or font height? Even one that doesn't let you select a font would be nice (eg: readLetters(Image image).
I've been looking into this a lot lately. Your best is simply Tesseract. If you need layout analysis on top of the OCR than go with Ocropus (which in turn uses Tesseract to do the OCR). Layout analysis refers to being able to detect position of text on the image and do things like line segmentation, block segmentation, etc.
I've found some really good tips through experimentation with Tesseract that are worth sharing. Basically I had to do a lot of preprocessing for the image.
Upsize/Downsize your input image to 300 dpi.
Remove color from the image. Grey scale is good. I actually used a dither threshold and made my input black and white.
Cut out unnecessary junk from your image.
For all three above I used netbpm (a set of image manipulation tools for unix) to get to point where I was getting pretty much 100 percent accuracy for what I needed.
If you have a highly customized font and go with tesseract alone you have to "Train" the system -- basically you have to feed a bunch of training data. This is well documented on the tesseract-ocr site. You essentially create a new "language" for your font and pass it in with the -l parameter.
The other training mechanism I found was with Ocropus using nueral net (bpnet) training. It requires a lot of input data to build a good statistical model.
In terms of invoking Tesseract/Ocropus are both C++. It won't be as simple as ReadLines(Image) but there is an API you can check out. You can also invoke via command line.
While I cannot recommend one in particular, the term you are looking for is OCR (Optical Character Recognition).
There is tesseract-ocr which is a professional library to do this.
From there web site
The Tesseract OCR engine was one of the top 3 engines in the 1995 UNLV Accuracy test. Between 1995 and 2006 it had little work done on it, but it is probably one of the most accurate open source OCR engines available
I think what you want is Conjecture. Used to be the libgocr project. I haven't used it for a few years but it used to be very reliable if you set up a key.
The Tesseract OCR library gives pretty accurate results, its a C and C++ library.
My initial results were around 80% accurate, but applying pre-processing on the images before supplying in for OCR the results were around 95% accurate.
What is pre-preprocessing:
1) Binarize the bitmap (B&W worked better for me). How it could be done
2) Resampling your image to 300 dpi
3) Save your image in a lossless format, such as LZW TIFF or CCITT Group 4 TIFF.