Image degradation

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Keithb
Posts: 5
Joined: 04.03.2006 00:56

Image degradation

Unread postby Keithb » 09.12.2006 22:53

When I upload some images to my site the quality is significantly downgraded. They look OK before uploading (jpg format). An example is here : www.wthrman.com/Photos/Storms/1.jpg

The problem area is with the dark sky. There are rippled patterns across it whereas in the original image (prior to upload) there is none of that. It looks like it's been painted. The image has been processed with HF.

Is there a way of overcoming this?

Thanks

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Ariel
Posts: 395
Joined: 26.10.2006 06:05

Unread postby Ariel » 10.12.2006 05:22

I don't see ripples in the sky. I do notice a lot of jpeg, so maybe you want to use a higher compression level (like 10). Did the picture have these ripple effects on the save tab?

lutz
Posts: 155
Joined: 14.04.2006 02:51

Unread postby lutz » 10.12.2006 06:44

Hello Keith,

I do see the ripples. Could you upload the image to "www.imageshack.us" for comparison?
As far as I understand you do not see the ripples locally in HF. Could it be that the images get processed again by an PHP-script on your web server (Image-Magick)? These might just be JPG banding artifacts?
Does the image on your website have the same file-size as your local file?

(I assume you are aware that repetitive saving of an image as JPG always goes along with image degradation)

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Ariel
Posts: 395
Joined: 26.10.2006 06:05

Unread postby Ariel » 10.12.2006 06:57

You could upload the image to this forum, too. Imageshack.us is good for hosting, so if the problem is actually with your server, that might fix the problem.

As I said before and as lutz reiterated, make sure you are saving the images without so much compression.

Keithb
Posts: 5
Joined: 04.03.2006 00:56

Unread postby Keithb » 10.12.2006 21:36

Thanks Lutz and Ariel,

Here is where I have uploaded it to imageshack. This is the original unprocessed image:

http://img175.imageshack.us/my.php?image=img0734ln6.jpg . There appears to be no banding.

I then reprocessed it with Helicon (4.5 by the way), but this time when I saved it to disk I used 82% compression; previously it had been 100% (ie in the image I posted before):

http://img184.imageshack.us/my.php?image=1mp5.jpg

There is noticeable banding in the clouds.

I have attached both images below, from which (at least on my screen) there is banding in both of them.

Ariel, to answer your question, yes, it did appear banded in the Save tab.

I suppose it must all come down to the compression of .jpg images. I did try png format but the file is then much larger and would be a problem for people viewing it with slow connections.
Attachments
IMG_0734_1.JPG
Original unprocessed image
IMG_0734_1.JPG (80.68 KiB) Viewed 6302 times
1.jpg
Processed image
1.jpg (96.69 KiB) Viewed 6302 times

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Ariel
Posts: 395
Joined: 26.10.2006 06:05

Unread postby Ariel » 10.12.2006 22:22

You mean right above the trees? Those are jpeg artifacts.

Make sure you resize the file (to like 800 by 500 pixels) before saving, also. Lots of times a server will not show the full image and will instead downsize it for viewing, and use some jpeg while doing so. If you make it so the file is small enough in the first place, you should have no problem.

lutz
Posts: 155
Joined: 14.04.2006 02:51

jpeg

Unread postby lutz » 11.12.2006 09:07

Hello Keith,

I did some tests ( just resizing, saving as jpg 82%) with HF, paint shop pro, and faststone. And I do ge the banding issue in all three apps, and surprisingly the least problems in Helicon Filter. I did not try to enhance the picture before my procedure. In my samples the banding is far less visible then in the one you posted.
http://img206.imageshack.us/my.php?imag ... 82jkg5.jpg
I guess your enhancements did enhance the problem a bit, too. In my experiments the banding seems to be clearly induced by the JPEG compression and it seems to be gone when using 86% quality in Faststone where you have more choices.
Somehow the subtle toning in the clouds seems to be very sensitive for JPEG artifacts. My guess, the only solution would be chosing a little less compression and to never save these images as jpgs - except for the final posting to the web.

Lets wait for Dan's insights.
(Perhaps Helicon Filter could offer some additional JPG compression adjustment steps?)

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Dan Kozub
Posts: 1157
Joined: 24.03.2004 18:14

Unread postby Dan Kozub » 19.12.2006 20:56

There is not much can be done in Helicon Filter as JPEG is a standard and the quality of all compressors is almost the same.

Please note, that the image on the Save tab is shown without any compression, so the artifacts must come from the original image and amplified during processing.


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