I came across this excellent tutorial on image processing by Bill Green - http://dasl.mem.drexel.edu/alumni/bGreen/www.pages.drexel.edu/_weg22/edge.html
He works with BMP formats in the tutorial since they are the simplest. I tried the sobel edge detection code, got it to compile and run. When I try this on the images on that web site (for example, LIAG.bmp, the photo of the lady), the code works just fine. However, when I get other .bmp images (for example, take any image and convert it at - http://www.online-convert.com/result/6c0ce763b5e6cadf3a76a966acdb9505) and the code spits out an image that can't be read by any image editor. The issue is most probably in the line -
nColors = (int)getImageInfo(bmpInput, 46, 4);
of his code. There seems to be some hard coding here which only works on the image sizes on his tutorial. The nColors variable is 256 for all images on his site, but 0 for all images I get otherwise. Can any one tell me how I might change this piece of code to generalize this?
The 46 in this line:
nColors = (int)getImageInfo(bmpInput, 46, 4);
...refers to the bit offset into the header of the BMP. Unless you are creating BMPs that do not use this file structure it should theoretically work. He is referring to 8-bit images on that page. Perhaps, 16 or 32-bit images use a different file structure for the header.
Read this Wikipedia page for more info: https://en.wikipedia.org/wiki/BMP_file_format#File_structure
Related
I have a file with a sequence of NxM unsigned integral values of fixed width - let's even assume they're single bytes - and I would like to "wrap" in some kind of common image file format. Preferably, something usable with popular image viewers; and otherwise with an image editor like GIMP.
What image format would require the minimum amount of conversion work, i.e. be as close as possible to just slapping some small header onto the raw data?
Notes:
This is a grayscale/intensity image - there are no color channels / interleaved values etc.
I don't care if the image format is row-major or column-major, i.e. if the image appears transposed relative to the order I wrote the data originally.
I've just noticed the Portable Pixmap Formats, which include the PGM format. The closest I've seen to a spec is on this page.
PGM files are supported by apps such as: Eye of Gnome (on Linux), IrfanView (on Windows), GIMP and others.
Create the image file programmatically
If I understand correctly, the following C function should convert the raw data OP has into a PGM file:
void write_pgm(FILE* file, size_t width, size_t height, uint8_t* data)
{
const char magic = "P5"; // for binary graymap
fprintf(file, "%2s %zu %zu 255\n", magic, width, height);
fwrite(data, 1, width * height, file);
}
This is a variation on a similar function for a PPM, here.
You can easily adapt this to whatever programming language you like.
Converting a file
So, suppose you've put your output in a file on disk. Apparently, there's a utility for making a PGM of it: rawtopgm. Here's a invocation for your case:
rawtopgm -bpp 1 -maxval 255 N M my_data_file > out.pgm
or, exploiting defaults:
rawtopgm N M my_data_file > out.pgm
pretty simple.
In file text.txt I have this sentenc:
"Příliš žluťoučký kůň úpěl ďábelské ódy."
(I think Windows uses Windows-1250 code page to represent this text.)
In my program I save it to a buffer
char string[1000]
and render string with ttf to SDL_Surface *surface
surface = TTF_RenderText_Blended(font, string, color);
/*(font is true type and support this text)*/
But it gives me not correct result:
I need some reputation points to post images
so I can only describe that ř,í,š,ž,ť,ů,ň,ď are not displayed correctly.
Is it possible to use ttf for rendering this sentence correctly?
(I tried also TTF_RenderUTF8_Blended, TTF_RenderUNICODE_Solid... with worse result.)
The docs for TTF_RenderText_Blended say that it takes a Latin-1 string (Windows-1252) - this will be why it isn't working.
You'll need to convert your input text to UTF-8 and use RenderUTF8, or to UTF-16 and use RenderUNICODE to ensure it is interpreted correctly.
How you do this depends on what platform your app is targeted to - if it is Windows, then the easiest way would be to use the MultiByteToWideChar Win32 API to convert it to UTF-16 and then use the TTF_RenderUNICODE_Blended to draw it.
My solution will be this:
Three input files. In first file there will be a set of symbols from czech alphabet.
Second file will be sprite bitmap file where graphic symbols will be sorted in the
same order as in first file. In my program symbols from third input file will be compared with symbols from first file and right section of sprite will be copied on sreen one by one.
I will leave out sdl_ttf. It has some advantages and disadvantages but I think it will work for my purposes.
Thanks for all responses
I am working on a project for a Bio-medical Imaging course (Note: it is a non-programming course, so asking for programming help is not cheating. Asking for conceptual help with planning would be cheating.) where I need to manipulate an image using different mathematical transforms. I am writing in C so it can be as fast as possible. I have finished the code for the mathematical transforms, but I have realized that I do not know how to turn a grayscale .png file into a 2-d matrix/array to compute with, and I do not know how to display a .png file in C. Can anyone help me?
I'm trying to turn the "image.png" image into a 2d array where each entry in the array has a value between 0 - 255 and corresponds with each pixel in "image.png". I also want to turn a 2d array where each entry corresponds to a pixel in the image and has a value between 0 - 255 into a new "image_two.png" file.
I'm a somewhat new programmer. I have a solid base in python programming, but C is new for me. I have done a lot of research and I have found a lot of people talking about using "this library" or "that library", or also "this library", but how do I use a downloaded library in C? It's unfamiliar territory for me as a python programmer :(
I'm using Ubuntu 12.04
To reiterate:
How do you read a grayscale .png image as a 2-d array/matrix in C?
How do you display a 2-d array/matrix as a grayscale image in C?
How do you use a downloaded library in C code (specifically for the two questions above)? I found out how to use these libraries.
EDIT: I am still having trouble figuring out how to create a grayscale 2d array out of a .png file and how to make a .png file out of a grayscale 2d matrix. Can anyone else help?
You can use a more general purpose image handling library and you might find it easier to use. I recommend FreeImage http://freeimage.sourceforge.net/. See the pixel access section of the manual to get access to the pixel data. You can then work with it directly or copy it into your own matrix.
To install a library in Linux, typically you will use the package manager. For example, in Debian (this includes Ubuntu) you might do:
$ apt-cache search libpng
You'll decide which package to install based on the results of running this command and then you will run
$ sudo apt-get install <package-name>
This command will likely install png.h in a location that is already included in gcc's search path. This means that to use png.h in your program, all you have to do is include it.
#include <png.h>
Skip to chapter 3 in the libpng manual for a walkthrough on reading a png file.
i got a question for reading an bmp image. How can i get the pixel value(R, G, B values) in an bmp image?
Can anyone help me using the C programming language?
Note: you may need to grab an extra byte for the alpha values if your BMP has alpha channel. In that case image would be image[pixelcount][4], and you would add another getc(streamIn) line to hold that fourth index. My BMP turned out to not need that.
// super-simplified BMP read algorithm to pull out RGB data
// read image for coloring scheme
int image[1024][3]; // first number here is 1024 pixels in my image, 3 is for RGB values
FILE *streamIn;
streamIn = fopen("./mybitmap.bmp", "r");
if (streamIn == (FILE *)0){
printf("File opening error ocurred. Exiting program.\n");
exit(0);
}
int byte;
int count = 0;
for(i=0;i<54;i++) byte = getc(streamIn); // strip out BMP header
for(i=0;i<1024;i++){ // foreach pixel
image[i][2] = getc(streamIn); // use BMP 24bit with no alpha channel
image[i][1] = getc(streamIn); // BMP uses BGR but we want RGB, grab byte-by-byte
image[i][0] = getc(streamIn); // reverse-order array indexing fixes RGB issue...
printf("pixel %d : [%d,%d,%d]\n",i+1,image[i][0],image[i][1],image[i][2]);
}
fclose(streamIn);
~Locutus
The easy way would be to find a good image manipulation library for your chosen platform and use that.
Linux ImLib / GDK-Pixbuf (Gnome/GTK) / QT Image (KDE/Qt) should be able to do what you need.
Windows I'm not familiar with the appropriate system library, but an MSDN Search for "Bitmap" is probably a good place to start.
Mac OSX Cocoa has some image manipulation capabilities, see this article.
The hard way would be to open the file and actually interpret the binary data within. To do that you'll need the BMP File Specification. I'd recommend trying the easy way first.
You need to study the BMP file format. It is easier to read uncompressed 24-bit BMP files. They just contain a header at the beginning and RGB values of each pixel.
To start with this, check the example of 2x2 bitmap image at http://en.wikipedia.org/wiki/BMP_file_format. Follow the below steps.
Create the 2x2 BMP image shown on Wikipedia.
Open the file in binary mode using your C program.
Seek to byte position 54.
Read 3 bytes.
The bytes would be 0, 0 and 255 respectively. (Not sure whether the order is RGB. I had done this long back and I think the order is not RGB. Just verify this.)
As simple as that! Study the header of the BMP to understand more about the format.
I'm trying to get the Spot color information from a TIFF file, it normally shows up under 'channels' in Photoshop. Each extra channel would have a name, which is usually a Pantone swatch name, and a CMYK equivalent.
So far, I'm getting the TIFFTAG_PHOTOSHOP with libtiff, and stepping through the blocks within. I'm finding the IRB WORD 0x03EE, which gives me the channel names, and IRB WORD 0x03EF which gives me their color equivalents...
BUT the color equivalents are in CIELab format (Luminance, and two axis of color space data) so I'm trying to use littleCMS to convert just a few TIFF packed Lab color to CMYK.
My question: Is there an easier way? The CMYK is just an approximation of the Pantone, so if there was a quick rough translation from Lab to CMYK, I would use it.
The answer was to use the photoshop docs to parse out the binary photoshop block in the tiff file and grab the fields I needed with bit manipulation.
littleCMS did the job of LAB -> CMYK just right.