防止GDI+ PNG 编码器将 Gamma 信息添加到 1 位 PNG
我想知道是否可以指示成像 PNG 编码器不向 1 位 PNG 添加任何伽玛和色度信息。
我正在为图像创建一个 2 调色板
ColorPalette* pal = (ColorPalette*)CoTaskMemAlloc(sizeof(ColorPalette) + 2 * sizeof(ARGB));
pal->Count = 2;
pal->Flags = 0;
pal->Entries[0] = MAKEARGB(0,0,0,0);
pal->Entries[1] = MAKEARGB(0,255,255,255);
if (FAILED(res = sink->SetPalette(pal))) {
return res;
}
CoTaskMemFree(pal);
，然后
BitmapData bmData;
bmData.Height = bm.bmHeight;
bmData.Width = bm.bmWidth;
bmData.Scan0 = bm.bmBits;
bmData.PixelFormat = PixelFormat1bppIndexed;
UINT bitsPerLine = imageInfo.Width * bm.bmBitsPixel;
UINT bitAlignment = sizeof(LONG) * 8;
UINT bitStride = bitAlignment * (bitsPerLine / bitAlignment); // The image buffer is always padded to LONG boundaries
if ((bitsPerLine % bitAlignment) != 0) bitStride += bitAlignment; // Add a bit more for the leftover values
bmData.Stride = bitStride / 8;
if (FAILED(res = sink->PushPixelData(&rect, &bmData, TRUE))) {
return res;
}
生成的 PNG 图像太大并且包含以下无用的标题：
sRGB、gAMA、cHRM
我实际上只期待 PLTE 而不是 sRGB。我如何设置编码器以跳过伽玛和色度计算？
I wonder if its possible to instruct the Imaging PNG Encoder not to add any gamma and chroma informations to a 1-bit PNG.
I am creating a 2 color palette for the image
ColorPalette* pal = (ColorPalette*)CoTaskMemAlloc(sizeof(ColorPalette) + 2 * sizeof(ARGB));
pal->Count = 2;
pal->Flags = 0;
pal->Entries[0] = MAKEARGB(0,0,0,0);
pal->Entries[1] = MAKEARGB(0,255,255,255);
if (FAILED(res = sink->SetPalette(pal))) {
return res;
}
CoTaskMemFree(pal);
and then just
BitmapData bmData;
bmData.Height = bm.bmHeight;
bmData.Width = bm.bmWidth;
bmData.Scan0 = bm.bmBits;
bmData.PixelFormat = PixelFormat1bppIndexed;
UINT bitsPerLine = imageInfo.Width * bm.bmBitsPixel;
UINT bitAlignment = sizeof(LONG) * 8;
UINT bitStride = bitAlignment * (bitsPerLine / bitAlignment); // The image buffer is always padded to LONG boundaries
if ((bitsPerLine % bitAlignment) != 0) bitStride += bitAlignment; // Add a bit more for the leftover values
bmData.Stride = bitStride / 8;
if (FAILED(res = sink->PushPixelData(&rect, &bmData, TRUE))) {
return res;
}
The resulting PNG image is way to large and contains the following useless headers:
sRGB,gAMA,cHRM
I was actually only expecting PLTE not sRGB. How do I have to setup the encoder to skip gamma and chroma calculations?
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我也有兴趣知道是否可能。我在 c++ 程序中使用 gdi+ 为网站生成 png，尽管我输入了完全相同的值，但 png 的颜色与 css 不同。通过删除 sRGB 内容，可以解决大多数浏览器中的伽玛问题。
我希望有一个解决方案！
I'm also interested to know if it's possible. I use gdi+ in a c++ program to generate png's for a website and the png's have different colors than the css although I put in the exact same values. By removing the sRGB stuff, that could solve the gamma problem in most browsers.
I hope there is a solution for this!
我通过实现 FreeImage 库 (http://freeimage.sourceforge.net/) 解决了这个问题。
我使用 GDI+ 创建位图，锁定其像素数据，创建自由图像位图，也锁定它并复制像素。
然后我让 freeimage 将其保存为 PNG 格式，瞧...正确的伽马信息，在每个浏览器中都很好。
它的开销有点大（尽管我感觉 FreeImage 保存图像的速度比 GDI+ 快得多，从而使整体过程更快）。当然，您的项目还需要一个带有 dll 的额外库。
I have resolved this by implementing the FreeImage library (http://freeimage.sourceforge.net/).
I create the bitmap with GDI+, I lock its pixeldata, create a freeimage bitmap, lock it too and copy the pixels.
Then I make freeimage save it to a PNG and voila... correct gamma information, good in every browser.
It's a little bit more overhead (although I have a feeling that FreeImage saves the images much faster than GDI+, making the overal process even faster). But of course, you will need an extra library with dll with your project.