I have an image which is representative of an Array2D:
template<class T = uint8_t>
Array2D<T> mPixData[4]; ///< 3 component channels + alpha channel.
The comment is in the library. I have no clues about the explanation.
Would someone:
explain what are the 3 component channels + alpha channel are about
show how I could resize this image based on the mPixData
Without know what library this is, here is a stab in the dark:
The type definition implies that it is creating a 2D array of unsigned chars (allowing you to store values up to 255.
template<class T = uint8_t> Array2D<T>
Then, mPixData itself is an array, which implies that at each co-ordinate, you have four values (bytes to contend with), 3 for the colours (let's say RGB, but could be something else) and 1 for Alpha.
The "image" is basically this three dimensional array. Presumably when loading stuff into it, it resizes to the input - what you need to do is to find some form of resizing algorithm (not an image processing expert myself, but am sure google will reveal something), which will then allow you to take this data and do what you need...
1) 3 component channels - Red Green Blue channels. alpha channel tells about image transparency
2) There are many algorithms you can use to resize the image. The simplest would be to discard extra pixels. Another simple is to do interpolation
The 3 component channels represent the Red Green Blue (aka RGB) channels. The 4th channel, ALPHA, is the transparency channel.
A pixel is defined by mPixData[4]
mPixData[0] -> R
mPixData[1] -> G
mPixData[2] -> B
mPixData[3] -> A
Therefore, an image can be represented as a vector or array of mPixData[4]. As you already stated, in this case is Array2D<T> mPixData[4];
Resize/rescale/resample an image is not a trivial process. There are lots of materials available on the web about it and I think you should consider using a library to do this. Check CxImage (Windows/Linux).
There are some code here but I haven't tested it. Check the resample() function.
Hi the 3 channels are the rgb + alpha channel. So red green and blue channels and the alpha channel. There are several methods to downscaling. You could take for example every 4 pixel, but the result would look quite bad, take a look at different interpolation methods e.g.: http://en.wikipedia.org/wiki/Bilinear_interpolation.
Or if you want to use a library use: http://www.imagemagick.org/Magick++/
or as mentioned by karlphillip:
http://www.xdp.it/cximage.htm
Related
I was wondering how to determine the equivalent of RGB values for a grayscale image. The original image is grayscale and everything I have found online is converting an RGB image pixel values to the grayscale pixel values. I already can read in the image. Ideally, this would be for xCode.
I was wondering if there was a class which would do this for me. If so, and you could point me to it, that would be great. I will read on it.
Any help is greatly appreciated.
NOTE: I am a beginner in C++ and do not have time to learn everything formally; I have to learn all of my programming on the fly.
You need more information to transform from a simple Greyscale to RGB, when you do reverse operation, the color information is "lost", as the three channels are set to same value(depending on the algorithm each channel will have a different/same weight in the final color computation).
Digital cameras, usually store more information per pixel, 12 bits per channel in 35mm and 14 bits per channel in medium format (those bits number are the average, some products offer less or even more quality).
Thanks to those additional bits per channel, the camera can compute the "real" color, or what it thinks is the real color based on some parameters.
TL;DR: You can't without more data from your source, in this case the image.
You can convert a gray value to RGB by setting each component of the RGB value to the gray value:
ColorRGB myColorRGB = ColorRGBMake(myGrayValue, myGrayValue, myGrayValue);
A C++ application running in another process passes in a char[] array of three-byte pixels (red, green, blue) to a go program. I've reconstructed this in go as a byte[] slice using cgo, but I'm unsure how to convert to an image. I can pass the width or height as well, if that is needed (I would imagine it would be).
I'm aware of the image.RGBA type, but the documentation seems to imply that those aren't just single-byte-per-color, and that assumes that there is an alpha channel, which my very simplistic bitmap does not have. Would converting the 3 byte values I have into something that works with image.RGBA be a solution? If so, how should I do that?
Alternatively, I could do the conversion in C/C++ before sending the values into a format that go recognizes (jpeg, gif, png). Either way works for my uses, but I don't know how to approach either.
The image package is based on interfaces. Just define a new type with those methods.
Your type's ColorModel would return color.RGBAModel, Bounds - your rectangle's borders, and At - the color at (x, y) that you can compute if you know the image's dimensions.
I want to draw with Direct2D frames which color channels are shifted on x-axis. I know I could set the composition mode to D2D1_COMPOSITE_MODE_PLUS and draw each color channel separately so I can shift them manually. But I want to know if there is another (maybe more efficient) way of drawing shapes with shifted color channels?
I attached an image which shows what I mean.
(I suggest to open this image in a new tab and zoom in to see the effect better)
The way this is typically done is to sample 3 pixels from the input image at a time, each separated by some amount in the x direction, and combine the red from one, the green from another, and the blue from the third. Unfortunately, I don't know DX2D at all, so I don't know the specifics of how it works there. But if you have a bitmap and a pointer to the pixels, you can simply subtract one (or more) pixels from that pointer, and add one or more pixels to the that pointer and read from those memory locations (being careful to account for image edges). Then pull the channels from the values you've read. For example:
RGBA8* pixel = baseAddressOfImage;
RGBA8* pixelMinus1 = pixel - 1;
RGBA8* pixelPuls1 = pixel + 1;
for each pixel in the output
{
result.red = pixelMinus1->red;
result.green = pixel->green;
result.blue = pixelPlus1->blue;
pixelMinus1++;
pixel++;
pixelPlus1++;
}
Note that you can add or subtract more than 1, but as mentioned above, you have to handle what happens at the edges in those cases.
I am working on a project to losslessly compress a specific style of BMP images that look like this
I have thought about doing pattern recognition, to find repetitive blocks of N x N pixels but I feel like it wont be fast enough execution time.
Any suggestions?
EDIT: I have access to the dataset that created these images too, I just use the image to visualize my data.
Optical illusions make it hard to tell for sure but are the colors only black/blue/red/green? If so, the most straightforward compression would be to simply make more efficient use of pixels. I'm thinking pixels use a fixed amount of space regardless of what color they are. Thus, chances are you are using 12x as many pixels as you really need to be. Since a pixel can be a lot more colors than just those four.
A simple way to do that would be to do label the pixels with the following base 4 numbers:
Black = 0
Red = 1
Green = 2
Blue = 3
Example:
The first four colors of the image seems to be Blue-Red-Blue-Blue. This is equal to 3233 in base 4, which is simply EF in base 16 or 239 in base 10. This is enough to define what the red color of the new pixel should be. The next 4 would define the green color and the final 4 define what the blue color is. Thus turning 12 pixels into a single pixel.
Beyond that you'll probably want to look into more conventional compression software.
Hello, here's a part of the code which Iam using,
b=(byte2&0xF8)<<8; //F8=11111000 5
g=(byte2&0xFC)<<3; //FC=11111100 6
r=(byte2&0xF8)>>3; //F8=11111000 5
grisColor=(r)|(g)|(b);
it takes a picture with an OV7670 camera in RGB 565, what do I have to modify in order to take a picture with only the red component?
Thanks a lot in advance
Just comment out the end of the last line:
grisColor=(r);//|(g)|(b);
and/or set g and b to zero.
Once you have the 5 bits of red, the next question is, do you want the output in grayscale (e.g. single octet), or RGB565 with just the red filled in (and green and blue zero), or RGB565 grayscale, or RGB24, ...?
I noticed that your goal is to get an 8bit grayscale image from the ov7670. You would get better results by setting the ov7670 to output yuv422 and "convert" that data to grayscale (Just use the Y component and ignore the U and V components).
I have a github repository that contains some useful functions for configuring the ov7670.
Check out the register list named yuv422_ov7670 https://github.com/ComputerNerd/ov7670-no-ram-arduino-uno/blob/master/ov7670_regs.h