Image processing-how does PHP remove some colors from an image to make it transparent?

Make an image transparent (based on the specified RGB color range. But in practice, the following code value is removed from white. What is the problem? {Code...} transparency of an image (based on the specified RGB color range. But in practice, the following code value is removed from white. What is the problem?

$ O_pic = '1.jpg '; // The starting Color Order to be processed $ begin_r = 215; $ begin_g = 215; $ begin_ B = 215; list ($ src_w, $ src_h, $ src_type) = getimagesize ($ o_pic); // get the original image information $ file_ext = get_ext ($ o_pic); // get the extension $ target_im = imagecreatetruecolor ($ src_w, $ src_h ); // new image if ($ file_ext = 'jpg ') // convert jpg to start {$ src_im = ImageCreateFromJPEG ($ o_pic); imagecopymerge ($ target_im, $ src_im, 0, 0, 0, 0, 0, $ src_w, $ src_h, 100); for ($ x = 0; $ x <$ src_w; $ x ++) {for ($ y = 0; $ y <$ src_h; $ y ++) {$ rgb = imagecolorat ($ src_im, $ x, $ y); $ r = ($ rgb> 16) & 0xFF; $ g = ($ rgb> 8) & 0xFF; $ B = $ rgb & 0xFF; if ($ r> $ begin_r & $ g> $ begin_g & $ B> $ begin_ B) {imagecolortransparent ($ target_im, imagecolorallocate ($ target_im, $ r, $ g, $ B ));}}}}

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Make an image transparent (based on the specified RGB color range. But in practice, the following code value is removed from white. What is the problem?

$ O_pic = '1.jpg '; // The starting Color Order to be processed $ begin_r = 215; $ begin_g = 215; $ begin_ B = 215; list ($ src_w, $ src_h, $ src_type) = getimagesize ($ o_pic); // get the original image information $ file_ext = get_ext ($ o_pic); // get the extension $ target_im = imagecreatetruecolor ($ src_w, $ src_h ); // new image if ($ file_ext = 'jpg ') // convert jpg to start {$ src_im = ImageCreateFromJPEG ($ o_pic); imagecopymerge ($ target_im, $ src_im, 0, 0, 0, 0, 0, $ src_w, $ src_h, 100); for ($ x = 0; $ x <$ src_w; $ x ++) {for ($ y = 0; $ y <$ src_h; $ y ++) {$ rgb = imagecolorat ($ src_im, $ x, $ y); $ r = ($ rgb> 16) & 0xFF; $ g = ($ rgb> 8) & 0xFF; $ B = $ rgb & 0xFF; if ($ r> $ begin_r & $ g> $ begin_g & $ B> $ begin_ B) {imagecolortransparent ($ target_im, imagecolorallocate ($ target_im, $ r, $ g, $ B ));}}}}

Do not use jpg. Because jpg does not support transparency, it is white. Use imagecreatetruecolor or imagecreatefrompng.