![]() ![]() If you want to see the alpha channel saved as a file called "alpha.png", you can use: magick xc:red \( +clone -threshold 0 -draw "rectangle 10,10 90,90" -write alpha.png \) -channel-fx '| gray=>alpha' result. \) -compose copy-alpha -composite result.png I have no idea why the following doesn't work: magick. The part after the parentheses forces that alpha channel into the original, red image making it transparent where the alpha channel is black and opaque where the alpha channel is white. This becomes the alpha channel in the next step. As the default draw colour is black, the nett result of everything inside the parentheses is that you will get a black rectangle on a white background. I then use -draw "rectangle x0,y0 x1,y1" to draw the "hole" you want to punch in the image. The -threshold 0 makes every pixel with brightness zero or more become white - so that means effectively all pixels become white. It does that with +clone which makes a copy of the original image - crucially the same size but without needing to know the size so it works for any image size. The part inside parentheses makes an alpha channel. That first part is no different from: magick -size 100x100 xc:red. Not sure why I can't find an easy way to do this, but the following should work for even magenta-coloured images: magick xc:red \( +clone -threshold 0 -draw "rectangle 10,10 90,90" \) -channel-fx '| gray=>alpha' result.png Then replace the alpha channel of the input with the new combined alpha channel. If your input image already has transparency, then you would have to extract its alpha channel and combine it with the rectangle image. For Windows, remove the \ from the parentheses and change the end of line \ to ^.įor ImageMagick 7, replace convert with magick The above is Unix syntax for ImageMagick 6. alpha off -compose copy_opacity -composite \ hand drawn pink rectangle title brush effect. The white will keep the image opaque and the black will show as transparent. a pink rectangular creative circle pink rectangular creative circle pink rectangle. So the simple answer is to create a black square in a white background and add that image as the alpha channel. You can only flood fill some region to replace a color with transparency. (His answer only works for ImageMagick 7). Gfx.DrawImage(image, new Rectangle(0, 0, bmp.Width, bmp.Height), 0, 0, image.Width, image.Height, GraphicsUnit.Pixel, attributes) īitmapImage.CacheOption = BitmapCacheOption.Here is an alternate to Mark's answer. ImageAttributes attributes = new ImageAttributes() Īttributes.SetColorMatrix(matrix, ColorMatrixFlag.Default, ColorAdjustType.Bitmap) Using (Graphics gfx = Graphics.FromImage(bmp)) create a graphics object from the image create a Bitmap the size of the image providedīitmap bmp = new Bitmap(image.Width, image.Height) Public Image SetImageOpacity(Image image, float opacity) Gfx.DrawImage(image, pwidth / 2 - image.PixelWidth / 2, pheight / 2 image.PixelHeight / 2) XImage image = XImage.FromBitmapSource(Convert(myTransparenImage)) You can use a Rounded Rectangle tool and draw your rectangle on a separate layer - just remember to turn the background off and save your image as a PNG file. Image myTransparenImage = SetImageOpacity(Image.FromFile("MyPath"), (float)opacityYouwant) // opacityYouWant has to be a value between 0.0 and 1.0 ![]() XGraphics gfx = XGraphics.FromPdfPage(page, XGraphicsPdfPageOptions.Append) This has already been answered so I am just sharing my code of doing so. What you can do is change the image you feed to PDF sharp. PDFSharp can not change the image opacity. ![]() The code below lets you change the opacity. I was looking in to this aswell now for making a watermark (companyLogo) to place over pdf sheets. ![]()
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