I m new in image processing field. I have worked with bmp images but currently i have a problem at hand which needs image to be converted into YCbCr color space before further processing. I have read about YCbCr and conversion process but the problem is i have no idea how i will store the YCbCr data in image format and which image format will support it.
i mean in bmp images rgb components are stored in bgr format, bytes should be multiples of 4 etc, but what about YCbCr? how they are represented?
i m sorry if this sounds very lame. I googled it a little but the thing is i don't think i m going in right direction. Actually this is for my final project and i m running out of time.
Update: actually there is no need to store it in some image container although tiff and jpeg can be used. i get around it by just converting rgb to YCbCr processing it and then converting it back to rgb pixel by pixel.
Both the formats only need three bytes for each pixel. So, as long as you store your pixels in some uncompressed format such as ppm, you do not need to bother about the conversion. When you are writing, put the Y into R, Cb int G and Cr into the blue bytes respectively. When you read in the values, it is up to to your program to interpret them - the default interpretation of most image processing programs is to treat them as RGB, but you can tell it to read them in as YCbCr
If you choose to store it in some compressed format such as jpeg, the values that you read back might not be the same as the ones that you store, but the decision depends on the accuracy that you need.
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I have huge images (1.800MP # 8bit or 16bit), all grayscale, no alpha, transparency or other stuff.
They may come as png, tiff, bmp, or even jpeg, so I need an image library to handle the reading, decompression and stuff.
After this, I just want to get an array with the grayscale pixel values out - preferrably 2d, but 1d is also alright. It also may be ushort all the time, even for the 8bit images.
I tried using the buid-int BitmapImage of C# - no luck, just throws exceptions for images this large.
Any other libraries that can give me the grayscale values, without hassle?
It will be faster if you use simple FileReader to read the content and generate your own array rather then looking for a library.
I want to know some information about YV12 image format.
1st question is YV12 Image format is equal to YUV420p format or YVU420p or YUV420Sp or YVU420Sp. I know that U and V have the same amount of memory in the format so in the case of planer image formats does swapping U and V makes some major difference. and if it does can some body explain me what is that.
Also i have heard that YV12 and NV12 are both 12 bits formats. Then can some body tell me that what is 4:2:0? it will be great if some can explain me in simple words thanks
According to this site, YV12 looks the same as NV12 except that NV12 is interleaved and YV12 is not. I think that YV12 correspond to YVU420p and NV12 is YVU420sp, but I'm not 100% sure about that.
What this means however, is that instead of having triplets [yuv][yuv][yuv][...] repeated all over your buffer to draw the image, one triplet per pixel, you have a large buffer of [y], then a buffer 1/4 of the [y] size containing all the [u], then another one 1/4 of [y] containing the [v]. For an image of 320x240 (76800 pixels), you will have 76800 Ys at the start of your buffer, then 19200 Us, then 19200 Vs.
In the NV12 case, you have a large buffer of [y], then a buffer 1/2 of the [y] size containing [uv] pairs. When drawing the image, or converting to another format such as RGB, you need a least 2 pointers, one that will read Ys and another one that will read the Us and Vs
When reading such as compressed format, the trick is that you have one Y per pixel, but the UV components change only on odd rows and odd columns and your eye will not see the difference. You reuse the same UV values for 4 pixels at a time while changing the Y for every pixel.
YUV is widely used in video processing, what you are talking about is chroma sub-sampling. The idea behind this, is that human eye is less sensitive to change in color, than to change in brightness.
You can find very thorough explanation of the process on wiki: https://en.wikipedia.org/wiki/Chroma_subsampling
Here is image of various chroma sub-sampling schemes used:
http://commons.wikimedia.org/wiki/File:Common_chroma_subsampling_ratios.svg
i was already able to convert a BMP image into binary memory stream but im confused with detecting LSB in pixel values..
I have the byte[] stream as '10101011101010101010010' ... .. ..
First is there a way that i can filter this binary stream to pixel values and detect LSB ?
If you want to read / write the Least Significant Byte to use the bitmap to hide information you will need to load the bmp data into an image, then access the pixel-data using GetPixel(). The BMP File itself might use RLL or some other compression so you cannot access the pixel data directly.
For detecting LSB in an image, it largely depends on the algorithm used, some are harder to detect as others. Do you have the description of the LSB-variant that might be in that image?
I want to create an 8-bit indexed image from a regular 32-bit Image object.
Bitmap img = new Bitmap(imgPath); // 32-bit
Bitmap img8bit = new Bitmap(imgW, imgH, Format8bppIndexed); // 8-bit
// copy img to img8bit -- HOW?
img8bit.Save(imgNewPath, ImageFormat.Png);
I cannot use SetPixel to copy it over pixel-by-pixel since Graphics doesn't work with indexed images.
How else?
I found a C# library that converts a bitmap into a palettized (8-bit) image. The technique is fast because it calls GDI32 (the windows graphics system) directly.
To convert to an 8bpp (palettized) image with a greyscale palette, do
System.Drawing.Bitmap b0 = CopyToBpp(b,8);
If you want to convert to an image with a different palette, look at the comments in the source code of CopyToBpp for suggestions. Note that, when you convert to a 1bpp or 8bpp palettized copy, Windows will look at each pixel one by one, and will chose the palette entry that's closest to that pixel. Depending on your source image and choice of palette, you may very well end up with a resulting image that uses only half of the colours available in the palette.
Converting an arbitrary RGBA image to an 8-bit indexed bitmap is a non-trivial operation; you have to do some math to determine the top 256 colors and round the rest (or do dithering, etc).
http://support.microsoft.com/kb/319061 has the details of everything except for a good algorithm, and it should give you an idea of how to get started.
I need to convert a RGB (jpg) grayscale CMYK using only to black channel (K).
I'm trying to do this with imageglue, but the result is not what i'm looking for since it converts the grays using the C,M and Y channel and leaves the black channel to 0%.
What I need is if anyone has experience in using any other library/api in .net that could work?
I would start by looking at the ColorConvertedBitmap class in WPF. Here is a link to the docs and a basic example:
http://msdn.microsoft.com/en-us/library/system.windows.media.imaging.colorconvertedbitmap(VS.85).aspx
Have you triedAForge.Net?
There is also ImageMagick, a c++ framework for image processing, with a .net wrapper (google for MagickNet)
Her is RGB to/from CMYK question which is related this one:
How is 1-bit bitmap data converted to 8bit (24bpp)?
I found The bitmap transform classes useful when trying to do some image format conversions but ... CYMK is one of the most complicated conversions you can tackle because there is more than one way to represent some colours. In particular equal CYM percentages give you shades of grey which are equivalent to the same percentage of K. Printers often use undercolour removal/transformation which normalises CYMK so that the a large common percentage is taken from CYM and transfered to the K. This is suppose to give purer blacks and grey tones. So even if you have a greyscale image represented using nothing but CYM with a zero black channel it could still print using nothing but K when you get it to a printer using undercolour removal.