Im working on resizing bitmap image and converting bitmap image to 8-bit (grayscale). But I have the problem that when I convert 32-bit image to 8-bit image, the result has another color overlay while it works perfectly on 24-bit. I guess the cause is in the alpha color. but I dont know where the problem exactly is.
This is my code to generate 8-bit palette color and write it after DIB part:
char* palette = new char[1024];
for (int i = 0; i < 256; i++) {
palette[i * 4] = palette[i * 4 + 1] = palette[i * 4 + 2] = (char)i;
palette[i * 4 + 3] = 255;
}
fout.write(palette, 1024);
delete[] palette;
As I said, my code works perfectly on 24-bit. In 32-bit the color is still kept after resizing, but when converting to 8-bit, it will look like this:
expected image (when converted from 24-bit) //
unexpected image (when converted from 32-bit)
This is how I get the colors and save it to srcPixel[]:
int i = 0;
for (int y = 0; y < height; y++) {
for (int x = 0; x < width; x++) {
int index = getIndex(width, x, y);
srcPixel[index].A = srcBMP.pImageData[i];
i += alpha;
srcPixel[index].B = srcBMP.pImageData[i++];
srcPixel[index].G = srcBMP.pImageData[i++];
srcPixel[index].R = srcBMP.pImageData[i++];
}
i += padding;
}
And this is the code I converted it by getting average of 4 colors A, B, G and R from that srcPixel[]:
int i = 0;
for (int y = 0; y < dstHeight; y++) {
for (int x = 0; x < dstWidth; x++) {
int index = getIndex(dstWidth, x, y);
dstBMP.pImageData[i++] = (srcPixel[index].A + srcPixel[index].B + srcPixel[index].G + srcPixel[index].R) / 4;
}
i += dstPadding;
}
If I remove and skip all alpha bytes in my code, when converting my image is still like that and I will have another problem is when resizing, my image will have another color overlay like the problem when converting to 8-bit: resizing without alpha channel.
If I skip the alpha channel while getting average (change into dstBMP.pImageData[i++] = (srcPixel[index].B + srcPixel[index].G + srcPixel[index].R) / 3, there is almost nothing different, the overlay still exists.
If I remove palette[i * 4 + 3] = 255; or doing anything with it, the result is still not affected.
Thank you very much.
You add alpha channel to the color and that's why it becomes brighter. From here I found that opaque is 255 and transparent 0 - therefore you add another channel which is set to 'white' to your result.
Remove alpha channel from your equation and see if I'm right.
As context, I'm working with building a topographic program which needs relatively extreme detail. I do not expect the files to be small, and they do not formally need to be viewed on a monitor, they just need to have very high resolution.
I know that most image formats are limited to 8 bpp, on account of the standard limits on both monitors (at a reasonable price) and on human perception. However, 2⁸ is just 256 possible values, which induces plateauing artifacts in a reconstructed displacement. 2¹⁶ may be close enough at 65,536 possible values, which I have achieved.
I'm using FreeImage and DLang to construct the data, currently on a Linux Mint machine.
However, when I went on to 2³², software support seemed to fade on me. I tried a TIFF of this form and nothing seemed to be able to interpret it, either showing a completely (or mostly) transparent image (remembering that I didn't expect any monitor to really support 2³² shades of a channel) or complaining about being unable to decode the RGB data. I imagine that it's because it was assumed to be an RGB or RGBA image.
FreeImage is reasonably well documented for most purposes, but I'm now wondering, what is the highest-precision single-channel format I can export, and how would I do it? Can anyone provide an example? Am I really limited, in any typical and not-home-rolled image format, to 16-bit? I know that's high enough for, say, medical imaging, but I'm sure I'm not the first person to try to aim higher and we science-types can be pretty ambitious about our precision-level…
Did I make a glaring mistake in my code? Is there something else I should try instead for this kind of precision?
Here's my code.
The 16-bit TIFF that worked
void writeGrayscaleMonochromeBitmap(const double width, const double height) {
FIBITMAP *bitmap = FreeImage_AllocateT(FIT_UINT16, cast(int)width, cast(int)height);
for(int y = 0; y < height; y++) {
ubyte *scanline = FreeImage_GetScanLine(bitmap, y);
for(int x = 0; x < width; x++) {
ushort v = cast(ushort)((x * 0xFFFF)/width);
ubyte[2] bytes = nativeToLittleEndian(cast(ushort)(x/width * 0xFFFF));
scanline[x * ushort.sizeof + 0] = bytes[0];
scanline[x * ushort.sizeof + 1] = bytes[1];
}
}
FreeImage_Save(FIF_TIFF, bitmap, "test.tif", TIFF_DEFAULT);
FreeImage_Unload(bitmap);
}
The 32-bit TIFF that didn't really work
void writeGrayscaleMonochromeBitmap32(const double width, const double height) {
FIBITMAP *bitmap = FreeImage_AllocateT(FIT_UINT32, cast(int)width, cast(int)height);
writeln(width, ", ", height);
writeln("Width: ", FreeImage_GetWidth(bitmap));
for(int y = 0; y < height; y++) {
ubyte *scanline = FreeImage_GetScanLine(bitmap, y);
writeln(y, ": ", scanline);
for(int x = 0; x < width; x++) {
//writeln(x, " < ", width);
uint v = cast(uint)((x/width) * 0xFFFFFFFF);
writeln("V: ", v);
ubyte[4] bytes = nativeToLittleEndian(v);
scanline[x * uint.sizeof + 0] = bytes[0];
scanline[x * uint.sizeof + 1] = bytes[1];
scanline[x * uint.sizeof + 2] = bytes[2];
scanline[x * uint.sizeof + 3] = bytes[3];
}
}
FreeImage_Save(FIF_TIFF, bitmap, "test32.tif", TIFF_NONE);
FreeImage_Unload(bitmap);
}
Thanks for any pointers.
For a single channel, the highest available from FreeImage is 32-bit, as FIT_UINT32. However, the file format must be capable of this, and as of the moment, only TIFF appears to be up to the task (See page 104 of the Stanford Documentation). Additionally, most monitors are incapable of representing more than 8-bits-per-sample, 12 in extreme cases, so it is very difficult to read data back out and have it render properly.
A unit test involving comparing bytes before marshaling to the bitmap, and sampled from the same bitmap afterward, show that the data is in fact being encoded.
To imprint data to a 16-bit gray scale (currently supported by J2K, JP2, PGM, PGMRAW, PNG and TIF), you would do something like this:
void toFreeImageUINT16PNG(string fileName, const double width, const double height, double[] data) {
FIBITMAP *bitmap = FreeImage_AllocateT(FIT_UINT16, cast(int)width, cast(int)height);
for(int y = 0; y < height; y++) {
ubyte *scanline = FreeImage_GetScanLine(bitmap, y);
for(int x = 0; x < width; x++) {
//This magic has to happen with the y-coordinate in order to keep FreeImage from following its default behavior, and generating
//the image upside down.
ushort v = cast(ushort)(data[cast(ulong)(((height - 1) - y) * width + x)] * 0xFFFF); //((x * 0xFFFF)/width);
ubyte[2] bytes = nativeToLittleEndian(v);
scanline[x * ushort.sizeof + 0] = bytes[0];
scanline[x * ushort.sizeof + 1] = bytes[1];
}
}
FreeImage_Save(FIF_PNG, bitmap, fileName.toStringz);
FreeImage_Unload(bitmap);
}
Of course you would want to make adjustments for your target file type. To export as 48-bit RGB16, you would do this.
void toFreeImageColorPNG(string fileName, const double width, const double height, double[] data) {
FIBITMAP *bitmap = FreeImage_AllocateT(FIT_RGB16, cast(int)width, cast(int)height);
uint pitch = FreeImage_GetPitch(bitmap);
uint bpp = FreeImage_GetBPP(bitmap);
for(int y = 0; y < height; y++) {
ubyte *scanline = FreeImage_GetScanLine(bitmap, y);
for(int x = 0; x < width; x++) {
ulong offset = cast(ulong)((((height - 1) - y) * width + x) * 3);
ushort r = cast(ushort)(data[(offset + 0)] * 0xFFFF);
ushort g = cast(ushort)(data[(offset + 1)] * 0xFFFF);
ushort b = cast(ushort)(data[(offset + 2)] * 0xFFFF);
ubyte[6] bytes = nativeToLittleEndian(r) ~ nativeToLittleEndian(g) ~ nativeToLittleEndian(b);
scanline[(x * 3 * ushort.sizeof) + 0] = bytes[0];
scanline[(x * 3 * ushort.sizeof) + 1] = bytes[1];
scanline[(x * 3 * ushort.sizeof) + 2] = bytes[2];
scanline[(x * 3 * ushort.sizeof) + 3] = bytes[3];
scanline[(x * 3 * ushort.sizeof) + 4] = bytes[4];
scanline[(x * 3 * ushort.sizeof) + 5] = bytes[5];
}
}
FreeImage_Save(FIF_PNG, bitmap, fileName.toStringz);
FreeImage_Unload(bitmap);
}
Lastly, to encode a UINT32 greyscale image (limited purely to TIFF at the moment), you would do this.
void toFreeImageTIF32(string fileName, const double width, const double height, double[] data) {
FIBITMAP *bitmap = FreeImage_AllocateT(FIT_UINT32, cast(int)width, cast(int)height);
//DEBUG
int xtest = cast(int)(width/2);
int ytest = cast(int)(height/2);
uint comp1a = cast(uint)(data[cast(ulong)(((height - 1) - ytest) * width + xtest)] * 0xFFFFFFFF);
writeln("initial: ", nativeToLittleEndian(comp1a));
for(int y = 0; y < height; y++) {
ubyte *scanline = FreeImage_GetScanLine(bitmap, y);
for(int x = 0; x < width; x++) {
//This magic has to happen with the y-coordinate in order to keep FreeImage from following its default behavior, and generating
//the image upside down.
ulong i = cast(ulong)(((height - 1) - y) * width + x);
uint v = cast(uint)(data[i] * 0xFFFFFFFF);
ubyte[4] bytes = nativeToLittleEndian(v);
scanline[x * uint.sizeof + 0] = bytes[0];
scanline[x * uint.sizeof + 1] = bytes[1];
scanline[x * uint.sizeof + 2] = bytes[2];
scanline[x * uint.sizeof + 3] = bytes[3];
}
}
//DEBUG
ulong index = cast(ulong)(xtest * uint.sizeof);
writeln("Final: ", FreeImage_GetScanLine(bitmap, ytest)
[index .. index + uint.sizeof]);
FreeImage_Save(FIF_TIFF, bitmap, fileName.toStringz);
FreeImage_Unload(bitmap);
}
I've yet to find a program, built by anyone else, which will readily render a 32-bit gray-scale image on a monitor's available palette. However, I left my checking code in which will consistently write out the same array both at the top DEBUG and the bottom one, and that's consistent enough for me.
Hopefully this will help someone else out in the future.
I have a native plugin in Unity that decodes H264 frames to YUV420p using FFMPEG.
To display the output image, I rearrange the YUV values into an RGBA texture and convert YUV to RGB using Unity shader (just to make it faster).
The following is the rearrangement code in my native plugin:
unsigned char* yStartLocation = (unsigned char*)m_pFrame->data[0];
unsigned char* uStartLocation = (unsigned char*)m_pFrame->data[1];
unsigned char* vStartLocation = (unsigned char*)m_pFrame->data[2];
for (int y = 0; y < height; y++)
{
for (int x = 0; x < width; x++)
{
unsigned char* y = yStartLocation + ((y * width) + x);
unsigned char* u = uStartLocation + ((y * (width / 4)) + (x / 2));
unsigned char* v = vStartLocation + ((y * (width / 4)) + (x / 2));
//REF: https://en.wikipedia.org/wiki/YUV
// Write the texture pixel
dst[0] = y[0]; //R
dst[1] = u[0]; //G
dst[2] = v[0]; //B
dst[3] = 255; //A
// To next pixel
dst += 4;
// dst is the pointer to target texture RGBA data
}
}
The shader that converts YUV to RGB works perfectly and I've used it in multiple projects.
Now, I'm using the same code to decode on iOS platform. But for some reason the U and V values are now shifted:
Y Texture
U Texture
Is there anything that I'm missing for iOS or OpenGL specifically?
Any help greatly appreciated.
Thank You!
Please note that I filled R=G=B = Y for the first screenshot and U for the second.(if that makes sense)
Edit:
Heres the output that I'm getting:
Edit2:
Based on some research I think it may have something to do with Interlacing.
ref: Link
For now I've shifted to CPU based YUV-RGB conversion using sws_scale and it works fine.
The problem was on this line :
uStartLocation + ((y * (width / 4)) + (x / 2));
It should be
uStartLocation + (((y / 2) * (width / 2)) + (x / 2));
Since int rounding was causing the whole frame to shift. Very silly error trying to optimize calculations.
Hope it helps someone.
I have the following code that creates a blank black image and then attempts to write to that image by modifying each pixel to red.
Magick::Image image(Magick::Geometry(1024, 1024),
Magick::Color(std::uint8_t(0), std::uint8_t(0), std::uint8_t(0)));
assert(image.channels() == 3 && "Created wrong image format.");
image.type(Magick::TrueColorType);
image.fillColor("black");
std::size_t w = image.columns();
std::size_t h = image.rows();
assert(image.columns() == 1024 && image.rows() == 1024);
Magick::Quantum *mpixels = image.setPixels(0, 0, w, h);
for (int row = 0; row < h - 1; ++row) {
for (int col = 0; col < w - 1; ++col) {
std::size_t offset = (w * row + col);
std::size_t moffset = image.channels() * offset;
mpixels[moffset + 0] = 255;
mpixels[moffset + 1] = 0;
mpixels[moffset + 2] = 0;
}
}
image.syncPixels();
image.write(out.c_str());
However, after inspecting the image it is still all black after changing the pixel values. What do I need to change to modify the pixel values?
I suspect that you are using the Q16 version of ImageMagick which means that each pixel channel value will be in the range 0-65535 and you are using 255 for the red channel which is really close to black. I think the following will fix your issue:
mpixels[moffset + 0] = 65535;
You could also decide to switch to the Q8 version of ImageMagick if channels in the range 0-255 would be sufficient for you.
I can find many examples on how to do this in managed c++ but none for unmanaged.
I want to get all the pixel data as efficiently as possible, but some of the scan0 stuff I would need more info about so I can properly iterate through the pixel data and get each rgba value from it.
right now I have this:
Bitmap *b = new Bitmap(filename);
if(b == NULL)
{
return 0;
}
UINT w,h;
w = b->GetWidth();
h = b->GetHeight();
Rect *r = new Rect(0,0,w,h);
BitmapData *lockdat;
b->LockBits(r,ImageLockModeRead,PixelFormatDontCare,lockdat);
delete(r);
if(w == 0 && h == 0)
{
return 0;
}
Color c;
std::vector<GLubyte> pdata(w * h * 4,0.0);
for (unsigned int i = 0; i < h; i++) {
for (unsigned int j = 0; j < w; j++) {
b->GetPixel(j,i,&c);
pdata[i * 4 * w + j * 4 + 0] = (GLubyte) c.GetR();
pdata[i * 4 * w + j * 4 + 1] = (GLubyte) c.GetG();
pdata[i * 4 * w + j * 4 + 2] = (GLubyte) c.GetB();
pdata[i * 4 * w + j * 4 + 3] = (GLubyte) c.GetA();
}
}
delete(b);
return CreateTexture(pdata,w,h);
How do I use lockdat to do the equivalent of getpixel?
Thanks
lockdat->Scan0 is a pointer to the pixel data of the bitmap. Note that you really do care what pixel format you ask for, PixelFormatDontCare won't do. Because how you use the pointer is affected by the pixel format. PixelFormat32bppARGB is the easiest, one pixel will be the size of an int, 4 bytes representing alpha, red, green and blue. And the stride will be equal to the width of the bitmap. Making it likely that a simple memcpy() will get the job done. Beware the bitmaps are stored upside-down.
Bitmap *m_image = new Bitmap(...) // a 24-bit RGB bitmap
BitmapData bmData;
Rect rect(0, 0, m_image->GetWidth(), m_image->GetHeight());
m_image->LockBits(&rect , ImageLockModeRead , PixelFormat24bppRGB,&bmData );
memcpy(your_bytes_buffer, bmData.Scan0, min(bmData.Height * bmData.Stride, your_buffer_size));
m_image->UnlockBits(&bmData);