I struggled for a long time devising bitmap problems for students in C++ that were easy. The problem is the libraries which are not easy to use. stbi, an include-only library completely solved this problem and now students can easily load and save images, allowing me to focus on giving them problems in creating various images in a bitmap class, and then writing it out with a simple call.
https://github.com/nothings/stb
However, I want to do the same thing for a microprocessor class involving ARM assembler and i want a 1 bit per pixel bitmap, ideally a png. I cannot find an example writing out a png of this type. Does anyone know how to do it, preferably using stbi or simply and portably between windows, mac and linux using some other library?
The following would do it for a png with 4 bytes per pixel. I want 1 bit per pixel.
stbi_write_png("testpng_4.png", width, height, CHANNEL_NUM, pixels, width*CHANNEL_NUM);
Alternatively, I found that in libpng++ there is a cleaner API than libpng.
constexpr int W = 128, H = 128;
png::image< png::index_pixel > image(W,H);
png::palette pal(2);
pal[0] = png::color(0,0,0);
pal[1] = png::color(255,0,0);
image.set_palette(pal);
Can anyone tell me how to get the address of the image to work with the raw bits? The C++ API provides square brackets and I dug down a bit but can't find anything I can take an address of.
Related
I realize this question might be closed with the "not enough research". However I did spent like 2 days googling for it and didn't find a conclusive answer.
Well I have an application that spawns a window, not written in c++. This application can have a c-interface with dlls. Now I wish to use the power of OpenCV, so I started on a dll to extend. Ss passing image data from/to the application is near impossible (only capable of passing c-strings & double values directly - using the hard drive for drawing is slowing down too much for real time image manipulation).
I am looking into letting opencv draw the image data directly - onto the window. I can gain the window handle easily, so would it then be possible to let openCV draw their data "over" the other window - or better into the other window?
Is this even possible with any library (FFMPEG, or something else)?
Yes, it's possible, but it's far from ideal. You can use GDI to draw on top of the other window (just convert IplImage to HBITMAP). Another technique is to do such drawing in a borderless layered window.
An easier approach is, since you own both applications, to write a function that passes an IplImage between them using standard C data types, after all, IplImage is nothing but a data type that is built from these standard types.
Here is how you will disassemble IplImage into 5 standard parameters:
The size (int, int) of the image (width/height);
The (int) bit depth of the image;
The number (int) of channels;
And the (unsigned char*) pixels of the image;
After receiving these parameters on the other side, you may wonder: how do I assemble a IplImage from scratch? Call cvCreateImageHeader() followed by cvSetData().
I've done a bit of research but haven't found anything useful so far.
In short I would like to be able to create a bitmap/canvas in memory and use an api which has functions for drawing primitive shapes and text on that bitmap and read the memory directly. This should be completely done in memory and not need a window system or something like Qt or GTK.
Why? I'm writing for the raspberry pi and am interfacing with a 256x64 4 bit greyscale OLED display over spi. This is all working fine so far. I've written a couple of functions for writing text etc, but am wondering if there is already a library I can use. I double buffer the display so I just need to manipulate the image in memory and then read the entire picture in one.
I can easily do this in windows but am not sure the best way to do this in linux
I've used Image Magick to do similar things. It supports Bitmap and SVG. http://www.imagemagick.org/script/index.php
I want to read the contents of every pixel in an image i have and convert it to a bit-stream (raw bits) or contain it in a 2-D array . Which would be the best place to start looking for such a conversion?
Specifics of the image : Standard test image called lena.bmp
size : 256 x 256
Bit depth of pixel : 8
Also I would like to know the importance of the number of bits per pixel with regards to this question since packing and unpacking will also be incorporated .
CImg is a nice simple, lightweight C++ library which can load and save a number of image formats (including BMP).
It's a single header file, so there's no need to compile or link the library. Just include the header, and you're good to go.
You should investigate OpenCV: a cross-platform computer vision library. It provides a C++ API as well as a C API, and it supports many image formats including bmp.
In the C++ interface, cv::Mat is the type that represents a 2D image. A simple application that loads and displays an image can be found here.
To learn how to access the matrix elements (pixels) you can check these threads:
OpenCV get pixel information from Mat image
Pixel access in OpenCV 2.2
Common Matrix Operations in OpenCV
OpenCV’s C++ interface offers a short introduction to cv::Mat. There has been many threads on Stackoverflow regarding OpenCV, there's a lot of valuable content around and you can benefit a lot by using the search box.
This page has a collection of books/tutorials/install guides focused on OpenCV, but this the newest official tutorial.
I'm currently doing a steganography project (for myself). I have done a bit of code already but after thinking about it, I know there are better ways of doing what I want.
Also - this is my first time using dynamic memory allocation and binary file I/O.
Here is my code to hide a text file within a BMP image: Link to code
Also note that I'm not using the LSB to store the message in this code, but rather replacing the alpha byte, assuming its a 32 bit per pixel (bbp) image. Which is another reason why this won't be very flexible if there are 1, 4, 8, 16, 24 bpp in the image. For example if it were 24 bbp, the alpha channel will be 6 bits, not 1 byte.
My question is what is the best way to read the entire BMP into memory using structures?
This is how I see it:
Read BITMAPFILEHEADER
Read BITMAPINFOHEADER
Read ColorTable (if there is one)
Read PixelArray
I know how I to read in the two headers, but the ColorTable is confusing me, I don't know what size the ColorTable is, or if there is one in an image at all.
Also, after the PixelArray, Wikipedia says that there could be an ICC Color Profile, how do I know one exists? Link to BMP File Format (Wikipedia)
Another thing, since I need to know the header info in order to know where the PixelArray starts, I would need to make multiple reads like I showed above, right?
Sorry for all the questions in one, but I'm really unsure at the moment on what to do.
The size of the color table is determined by bV5ClrUsed.
An ICC color profile is present in the file only if bV5CSType == PROFILE_EMBEDDED.
The documentation here provides all that information.
Then, 24-bit color means 8 red, 8 green, 8 blue, 0 alpha. You'd have to convert that to 32-bit RGBA in order to have any alpha channel at all.
Finally, the alpha channel DOES affect the display of the image, so you can't use it freely for steganography. You really are better off using the least significant bits of all channels (and maybe not from all pixels).
How can I do simple thing like manipulate image programmatically ? ( with C++ I guess .. )
jpgs/png/gif .....
check out BOOST , it has a simple Image Processing Library called GIL. It also has extensions to import common formats.
http://www.boost.org/doc/libs/1_39_0/libs/gil/doc/index.html
Using .NET you have two options:
GDI+ from System.Drawing namespace (Bitmap class)
WPF engine wich can do a lot of things
If you want low level processing you can use unsafe code and pointers.
A Bitmap or Image is just a big array of bytes.
You need to learn:
what is a stride (extra padding bytes after each row of pixels)
how to compute the next row or a specific pixel location using width, height, stride
the image formats RGB, ARGB, white&black
basic image processing functions (luminosity, midtone, contrast, color detection, edge detection, matrix convulsion)
3D vectorial representation of a RGB color
Depending on how fancy you want to get, you may want to look at OpenCV. It's a computer vision library that has functions ranging from reading and writing images to image processing to advanced things like object detection.
Magick++ is a C++ API for the excellent ImageMagick library.
An advantage of ImageMagick is that it can be used from the command-line and a bunch of popular scripting and compiled languages too, and some of those might be more accessible to you than C++.