#40158 [Opn]: Artifact left on transparent pngs using image filters

ID: 40158 Updated by: pajoye@php.net Reported By: henus at mail dot ru Status: Open Bug Type: GD related Operating System: Windows XP PHP Version: 5.2.0 Assigned To: pajoye New Comment: Can you *PLEASE* confirm that it works when you disable alpha blending? Answer should be Yes or No, I got the details already. I really do not have the time to explain/ask again and again the same thing. About imagefill, yes, that's a bug. Please open a new one if you like. I will fix it as soon as possible. Previous Comments: ------------------------------------------------------------------------ [2007-01-19 11:53:03] henus at mail dot ru Yes, the is global problem with alphablending in libgd\gd.c but about "imagealphablending($mask, false); //<<< Important!": i absolutely should not care about ebabling\disabling imagealphablending before imagefilter, because of function shoud colorize image by new values of red,gree,blue (!!!there is no alpha in parameters) if IMG_FILTER_COLORIZE will have in parameters alpha, if alphablending enable, value of alpha should allow for calculation of new color values (in gdImageColor it will before new_pxl = gdImageColorAllocateAlpha(src, (int)r, (int)g, (int)b, a);) and gdImageSetPixel shoul with disabled alphablending. otherwise function work like merging of two images with alphablending. where: first image - source image from function parameters. second image - correct colorized copy of source image. it is not logically. it is incorrect. another bug in imagefill: this function not only fill image, it is also disable alphablending. php example: <? /* first colorizing */ $im1=imagecreatetruecolor(1,1); imagealphablending($im1, TRUE); $c01=imagecolorallocatealpha($im1,255,0,0,63); imagefill($im1,0,0,$c01); $c01=imagecolorsforindex($im1,imagecolorat($im1,0,0)); imagefilter($im1, IMG_FILTER_COLORIZE, -255, 255, 0); $c1=imagecolorsforindex($im1,imagecolorat($im1,0,0)); /* second colorizing */ $im2=imagecreatetruecolor(1,1); imagealphablending($im2, TRUE); $c02=imagecolorallocatealpha($im2,255,0,0,63); imagefill($im2,0,0,$c02); $c02=imagecolorsforindex($im1,imagecolorat($im1,0,0)); /* att!!! after imagefill another enabling alphablending */ imagealphablending($im2, TRUE); imagefilter($im2, IMG_FILTER_COLORIZE, -255, 255, 0); $c2=imagecolorsforindex($im2,imagecolorat($im2,0,0)); print"<br>before 1 - "; print_r($c01); print"<br>after 1 - "; print_r($c1); print"<br><br>before 2 - "; print_r($c02); print"<br>after 2 - "; print_r($c2); ?> results: before 1- Array ( [red] => 255 [green] => 0 [blue] => 0 [alpha] => 63 ) after 1 - Array ( [red] => 0 [green] => 255 [blue] => 0 [alpha] => 63 ) before 2- Array ( [red] => 0 [green] => 255 [blue] => 0 [alpha] => 63 ) after 2 - Array ( [red] => 126 [green] => 128 [blue] => 0 [alpha] => 31 ) where: after 1 - correct result of IMG_FILTER_COLORIZE, because of imagefill disable alphablending after 2 - incorrect result of IMG_FILTER_COLORIZE, because of after imagefill i manually enable alphablending disabling alphablending in code it is good solutions for gdImageColor, but after it is necessary to restore old value of alphaBlendingFlag. ------------------------------------------------------------------------ [2007-01-18 19:54:09] pajoye@php.net "pixel from edge with coord (95,11) have wrong color. red-98 green-98 blue-164 (why is red>0 and green>0 ????????? after substracting 255???) (should be red-0 green-0 blue-102)" It is blended over the destination pixel. You have to disable alpha blending *before* the imagefilter call. This image: http://blog.thepimp.net/misc/bug40158_black_filtered_mask.png shows exactly what you are trying to do (blue, black or purple, it really does not matter), the script being: $mask=imagecreatefrompng("40158.png"); imagealphablending($mask, false); //<<< Important! imagefilter($mask, IMG_FILTER_COLORIZE, -255, -255, -255); //<<< save alpha, so we see its value imagesavealpha($mask, true); imagepng($mask,"mask1.png"); Using your last example, the resulting image is like your "result_correct3.png". ------------------------------------------------------------------------ [2007-01-18 19:37:49] henus at mail dot ru it`s not solve my problem.... :( first - about blue color - look at my submission from [18 Jan 11:03am UTC] if use imagefilter($mask, IMG_FILTER_COLORIZE, -255, -255, -255); the result is http://www.fort-ross.ru/henus/gd/result_incorrect.png with legibly visible artefacts. second - image http://blog.thepimp.net/misc/bug40158_result.png also has artefacts at the adges... pixel from edge with coord (95,11) have wrong color red-98 green-98 blue-164 (why is red>0 and green>0 ????????? after substracting 255???) (should be red-0 green-0 blue-102) third - look at my submission from [18 Jan 5:56pm UTC] why is 255-255=126???????????????? one more demo - using imagefilter($mask, IMG_FILTER_COLORIZE, -255, -255, 0); mask - http://fort-ross.ru/henus/gd/mask3.png incorrect image - http://fort-ross.ru/henus/gd/result_incorrect3.png correct image - http://fort-ross.ru/henus/gd/result_correct3.png ------------------------------------------------------------------------ [2007-01-18 18:51:59] pajoye@php.net (rgba(255,0,0,xxx)) should have been (rgba(0,0,255,xxx)) but you noticed it :) ------------------------------------------------------------------------ [2007-01-18 18:51:04] pajoye@php.net An absolute black image is not what you should expect. imagefilter($mask, IMG_FILTER_COLORIZE, -255, -255, 0); will replace the white color with blue (you remove all components but the blue): http://blog.thepimp.net/misc/bug40158_filtered_mask.png imagecopy($imagemain, $mask, 0, 0, 0, 0, $imagewidth, $imageheight); will copy it over the $imagemain, the border of the quadrant will be blended over black: http://blog.thepimp.net/misc/bug40158_result.png Each pixel in your circle are rgb(255,255,255) with some alpha value in the edges (and only in the edges). You are substracting 255 to the R and G component, the result is blue. Now, take a look at this image: http://blog.thepimp.net/misc/bug40158_correct_filtered_mask.png It is what you are expecting (if I understand correctly your problem). The edges of the circle have a blue color with various alpha values (rgba(255,0,0,xxx)). You can reproduce it by disabling the alpha blending mode in the mask image (imagealphablending($mask, false); ). The alpha component will be kept and stored in the image instead of being used as a blending value. Let me know if that solves your problem. By the way, COLORIZE uses gdImageColor. The lines you are referring to are in the contrast function. ------------------------------------------------------------------------ The remainder of the comments for this report are too long. To view the rest of the comments, please view the bug report online at http://bugs.php.net/40158 -- Edit this bug report at http://bugs.php.net/?id=40158&edit=1