Watermark Degrades photo, badly.

kevinpowertv · July 23rd, 2009, 12:01 PM

I have a strange problem. When I upload an image to photopost with a PNG watermark, the entire image is degraded enormously. I have the quality setting to 100%, there is no resizing, and I'm using GD to process the images. The PNG I'm using is also a hi res file with a little transparency.

Here is an example of the same image uploaded with a watermark and without. Notice the color saturation changes dramatically and there is a slight fuzziness in the watermarked image.

Without watermark:
http://www.streetlegaltv.com/photos/data/623/HDR1_1.jpg

With watermark:
http://www.streetlegaltv.com/photos/...23/HDR1_11.jpg

Chuck S · July 23rd, 2009, 12:52 PM

You know I clicked both of those links to open in a new window and I tell you I see two identical photos one with and one without a watermark. I am not sure what color degradation you are referring to here.

The two photos your linking are identical except for the watermark.

kevinpowertv · July 23rd, 2009, 01:15 PM

They are not nearly identical. Put the images side by side and you'll see the color saturation on the un-watermarked image is much better than the watermarked image. Look specifically at the reds, yellows, and whites. The image with the watermark is quite a bit lighter as well.

See attachment.

kevinpowertv · July 23rd, 2009, 01:17 PM

Uploading an attachment was a bad idea... here is the comparison file un changed...

http://www.powertvmedia.com/test_image.png

Chuck S · July 23rd, 2009, 01:32 PM

I did not look at attachments. I opened both links in a different tab in the browser viewed the full images and went back and forth and see no difference other than a watermark

At any rate I would not say badly as the photos are nearly identical

I can tell you as far as watermarks you want to use absolutely transparent watermarks not semi-transparent. The watermarking itself is not done by photopost. It is an internal function in GD2 and PHP so not sure I can tell you anything that can help you with that. We simply use the normal watermarking strings in present in GD2.

kevinpowertv · July 23rd, 2009, 01:35 PM

Well, you can see from my example that the watermarks I'm using are not transparent themselves, but are set to be a 24 bit PNG file. From a photographers perspective, the differences between the two photos is dramatic enough to be a problem, at least for me. Can you recommend anything to remedy the problem? Is there any settings I can change for GD2?

powertvmark · July 23rd, 2009, 01:35 PM

I do the vast majority of the photography around here. We were covering races and not using stamps for a little while. As soon as we started using the stamps, I noticed an immediate reduction on the quality versus an unstamped photo.

http://www.streetlegaltv.com/photos/.../IMG_58871.JPG

http://www.streetlegaltv.com/photos/...3/IMG_5887.JPG

powertvmark · July 23rd, 2009, 01:40 PM

I could do some searching to find some really obvious ones, but these are just from this last weekend.

Chuck S · July 23rd, 2009, 01:52 PM

Well You can try experimenting with your actual watermark to see if thats causing your issue. There is nothing in the program I can tell you to do because as previously stated the routine is cut and dry. GD2 is part of PHP and uses a specific set of PHP recognized internal commands. There is nothing to edit or anything I could tell you to help there.

Something in that specific watermark is messing with reds if that makes sense because there seems to be the only pattern I see here.

kevinpowertv · July 23rd, 2009, 02:19 PM

Does the upload script tell GD2 to process the photo using 256 colors instead of 16bit true color? Because that would certainly cause this issue. There is an attribute for ImageCreateTrueColor where this value can be changed, but I couldn't find reference to it being used in Photopost.

Chuck S · July 23rd, 2009, 03:53 PM

The watermark process does not use that function.

The Truecolor thing is used in creating an image not the watermark

Watermarking uses this

Code:

Content visible to verified customers only.

You can see if your server has mogrify ( Imagemagick ) and use that instead of GD2

PHP: imagecreatetruecolor - Manual

imagecreatruecolor has no setting for bit rate it is only height and width. I do not see anything special that needs to be done for a 24bit png.

kevinpowertv · July 24th, 2009, 11:08 AM

imagecreatetruecolor is not just for height and width. It is a setting you can set to process the image. Once the watermark gets put on the image, doesn't it use GD2 to process the image and merge the PNG and the source image together?

Chuck S · July 24th, 2009, 12:26 PM

Kevin

I linked the imagecreatetruecolor manual from PHP site right above. Please tell me where you input anything but height and width. I beleive my links have shown the true operation of that function.

I beleive what happens is yes imagecreatetruecolor is used to process an image but thats done regardless of a watermark of not. There is no extra bit variable in that function.

Now the watermark if I am not mistaken takes an already processed image which happens second before of whatever and places a watermark on the photo. I beleive ImageCopy is used for that

Code:

Content visible to verified customers only.

Thats why I linked the gd watermark code right above to show what goes on. I do beleive we use the correct strings as noted in the PHP site requirements. If there is an issue with GD2 itself and color sampling I dont know how we can rectify that. I can tell you this would not happen with Imagemagick.

Chuck S · July 24th, 2009, 01:09 PM

Kevin

The only thing I can think of is an issue with the GD2 color libraries on the server? Please tell you if you have any supporting information other then what I am finding.

Here is my test

Imagemagick and watermark flawless

IMG_58871 - ReefTalk Gallery

GD2 with and without watermark

IMG_588711 - ReefTalk Gallery
IMG_588712 - ReefTalk Gallery

Both to me are of less quality than Imagemagick. In fact I think both with and without watermarking are of the same lesser quality

Now I use 100% for images so I dont think there is an issue here. In fact the only PHP GD2 command which accepts any kind of quality setting is ImageJPEG and we do input a quality there. Thus I process that file using GD2 with or without a watermark on my server you can see there is definate color degrading using GD2.

Given that this degredation is happens regardless of watermark or no watermark as shown in my testing and also to the fact that all the image processing strings this might either be a limitation on GD2 and color sampling or the version on the servers color libraries.

kevinpowertv · July 24th, 2009, 01:15 PM

Yeah, thats a good comparison. I'll try ImageMagick and see if that fixes it.

Chuck S · July 24th, 2009, 01:20 PM

yeah no problem. I did what digging I could do to see if I could see anything. You said there was a bit quality setting for that one function which there was not so I had to do research on that.

In the long run I just went to my site and thats what I come up with which is why I always have used Imagemagick. It is just so much better than GD2.