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09/25/2002 10:12:37 AM · #1
I receieved a comment on my submission "...artifacts are unfortunate. Compress with less aggressive settings." What exactly does this means?

I'm using Photoshop 7.0.

* This message has been edited by the author on 9/25/2002 11:04:40 AM.
09/25/2002 10:18:48 AM · #2
JPG files give people the ability to compress the image so that it can be downloaded faster on the Internet. The nice thing about this is that you can take an image and reduce the file size quite a bit. The bad thing is that the more compression that's used on the file, the more "funky" it will look. It will lose sharpness, and you'll be able to notice pixels that are noticeably altered.

When I submit shots to DPC, I tinker with the compression settings to find the one that makes the file size as close to the 150K limit as possible. This helps ensure that the shots will look as good as possible without the compression making them fuzzy and otherwise distorted.

Check whatever program you're using for your images to find the .jpg compression feature -- if you post the name of the program you're using, I'm sure folks here can help you find exactly where that is.
09/25/2002 10:35:03 AM · #3
Originally posted by IGJOE:
I receieved a comment on my submission "...artifacts are unfortunate. Compress with less aggressive settings."

unfortunately, my submission for this week also received a comment along these lines

the unfortunate part is that the person was completely wrong - what might appear to be "noise" in the background is actually REAL background in the haze - trees, hills, buildings - NOT a degraded sky darkening into the horizon ----- and IF YOU LOOK, it's not even that questionable

lesson: not only do people vote from different perspectives, some people don't even need to see your picture to vote on it

09/25/2002 10:55:11 AM · #4
I have seen quite a bit of confusion in comments that I have read... some people seem to use 'over sharpened', 'compression artifacts', and
'noise' fairly interchangeably. I think I will try to create some examples of each of these situations and post the resulting photos here so that everyone will have the opportunity to see what each situation looks like and what is different about them... maybe i'll make this a chat topic for the chat room later this week :)
09/25/2002 10:56:44 AM · #5
Originally posted by spiderman:
Originally posted by IGJOE:
[i]I receieved a comment on my submission "...artifacts are unfortunate. Compress with less aggressive settings."


unfortunately, my submission for this week also received a comment along these lines

the unfortunate part is that the person was completely wrong - what might appear to be "noise" in the background is actually REAL background in the haze - trees, hills, buildings - NOT a degraded sky darkening into the horizon ----- and IF YOU LOOK, it's not even that questionable

lesson: not only do people vote from different perspectives, some people don't even need to see your picture to vote on it

[/i]

LOL! I knew the voters were good... But to not even have to see the picture! Wow...



* This message has been edited by the author on 9/25/2002 10:55:13 AM.
09/25/2002 12:51:32 PM · #6
Originally posted by spiderman:
lesson: not only do people vote from different perspectives, some people don't even need to see your picture to vote on it

Well, if voting was fair, Al Gore would be the US President and George Bush would be mismanaging a baseball team or oil company or something :)

<Ducks and runs>
09/25/2002 02:00:47 PM · #7
For an example:

DPReview JPEG artifact article.

I am VERY tendent to comment on obvious JPG artifacts. Almost every semi-serious editing suite I've ever used allows adjustment of JPEG compression at file save time. (PhotoShop, Photo Paint, Paint Shop Pro, The GIMP, and so on)

I will always comment on the artifacts, but I will only knock a point based on apparent filesize. If the photo I'm looking at is close to 150K, I assume that JPEG compression was set as low as possible without breaking the 150K rule. A 40K image, however, will get a point detracted, and a comment made because some measure of those artifacts could have been avoided.

It's a learning process, and hopefully, commenting on technical problems which are not necessarily photographic in nature will help improve people's presentation of their own work.

And, for the record... I am pretty freakin' good at identifying these things, but I can make mistakes, so if I incorrectly identified JPEG artifiacts on your photos, I apologize.

Mark



* This message has been edited by the author on 9/25/2002 2:02:00 PM.


* This message has been edited by the author on 9/25/2002 2:02:43 PM.
09/25/2002 02:06:46 PM · #8
MJ, could you point me to a few examples here on DPC where JPG artifacts have been a problem? I would like to use them as examples when I do the chat session on this tomorrow night.... :)
09/25/2002 02:22:19 PM · #9
Will do. I'm procrastinating in an IBM class, anyway :)

mjc
09/25/2002 02:26:41 PM · #10


Well, if voting was fair, Al Gore would be the US President and George Bush would be mismanaging a baseball team or oil company or something :)


Also... Nixon would've been the US President in 1960 instead of Jack Kennedy. Then, Nixon wins reelection in 1964 and Watergate never happens.

Coulda, shoulda, woulda...

Do we really need to rehash this election thing here? The newspapers were all over this thing, and nearly two years later they haven't found anything to suggest Gore won.

Now back to your regularly scheduled discussion of JPEG artifacts...



09/25/2002 03:26:25 PM · #11
Just a heads up about 'progressive' JPG images. The ones that load really quickly at a very low resolution and then progressively improve in resolution as the file continues to download...

Some folks who are on dialup connections, and who run into a modem hiccup might see the image stuck at the next-to-last progression for a bit and think the image looks crummy, not realizing that the image is not finished loading. I avoid using progressive JPG for just this reason, but it might lead some to make 'artifact' comments if they aren't watching their browser progress bar.

That may not be the problem here at all, but just a thought.
09/25/2002 04:33:54 PM · #12
I would assume that a "progressive" JPEG would be larger at a given setting than norma. Does anyone know if theis is generally true, and if so, how much of a "hit" do you take? For DPC, I just use the normal setting at a level which comes as close as possible to 150k without going over (usually 6-8 in PS 5.x).
09/25/2002 04:35:21 PM · #13
Originally posted by jperez1690:
Just a heads up about 'progressive' JPG images. The ones that load really quickly at a very low resolution and then progressively improve in resolution as the file continues to download...


Agreed. This can be a problem in interpreting artifacts properly. The best way to determine which you are seeing is to ask yourself if the distortion in the image is uniform, or seems to be local to edges and gradients within the picture. The progressive JPG decoding renders an image in decreasing degrees of distortion as the image loads, but the distortion is uniform throughout the frame, whereas jpeg artifacts are limited to very specific areas within the image.

mjc


09/25/2002 05:13:35 PM · #14
I have looked at a few photos around here and seen some where I believe the image quality could be improved with less compression.

I am going to do an experiment with jpeg compression when I get home and I will post the results to a pbase folder. I am going to take the same original image and save it at different compression levels and see where I start to see a difference. I have played around with this briefly in the past and i can rarely tell any difference between a 150k file size and a 100k file size. Actually, i will try this with two or three images since compression artifacts would become more readily visible at different levels on different images...
09/25/2002 05:29:21 PM · #15
John, I was taught that the color red is particularly bad at artifacting. so bad in fact that it was recommended that if there is large amounts it is better to save as a gif.
09/25/2002 05:47:50 PM · #16
Originally posted by aelith:
John, I was taught that the color red is particularly bad at artifacting. so bad in fact that it was recommended that if there is large amounts it is better to save as a gif.

GIF compression works by looking along a horizontal row for the same color. For example, if there are 200 blue pixels in a horizontal row, GIF compression will 'shorten' this to 'the next 200 pixels are blue' (this is just a simple example, and avoiding the actual data structure and math). Therefore, GIF compression works best when you have solid areas of the same color (in the horizontal direction).

aelith, I don't believe that the color red has anything to do with JPG vs GIF (John can correct me if I'm wrong). What you may be thinking of is the issue that CRT monitors have with reproducing the color red. You will especially see this issue on the cheap TVs you see lined up in the electronic stores. When a picture appears that has lots of red the less expensive TVs will really have trouble...

Alan
09/25/2002 06:01:55 PM · #17
Originally posted by JohnSetzler :
I have seen quite a bit of confusion in comments that I have read... some people seem to use 'over sharpened', 'compression artifacts', and
'noise' fairly interchangeably. I think I will try to create some examples of each of these situations and post the resulting photos here so that everyone will have the opportunity to see what each situation looks like and what is different about them... maybe i'll make this a chat topic for the chat room later this week :)


John,

I previously posted some Sharpening examples at pBase -- I don't know if they will be at all helpful, but you are welcome to copy or link to them if they are...
I sometimes comment that I think photos are over-sharpened, so I'm curious to see your examples and discussion; do you archive the chat sessions for those who can't "attend?"
--Paul

* This message has been edited by the author on 9/25/2002 6:02:13 PM.
09/25/2002 06:05:28 PM · #18
Originally posted by myqyl:
Originally posted by spiderman:
[i]lesson: not only do people vote from different perspectives, some people don't even need to see your picture to vote on it


Well, if voting was fair, Al Gore would be the US President and George Bush would be mismanaging a baseball team or oil company or something :)

<Ducks and runs>[/i]
Ummmm I think it's best we try to avoid political references here. Or else I'll bring God into it too...lol Like "Thank GOD Gore lost, He answered my prayers!" See prayer DOES work!!! Or should I just say nothing at all? Quoting an Alison Krauss song "You say it best, when you say noting at all." ;-) Ok I'll quit. It's best if we stick to digital photography here.




* This message has been edited by the author on 9/25/2002 6:11:09 PM.
09/25/2002 07:11:55 PM · #19
Originally posted by mjcecil:
For an example:

DPReview JPEG artifact article.

I am VERY tendent to comment on obvious JPG artifacts. Almost every semi-serious editing suite I've ever used allows adjustment of JPEG compression at file save time. (PhotoShop, Photo Paint, Paint Shop Pro, The GIMP, and so on)

I will always comment on the artifacts, but I will only knock a point based on apparent filesize. If the photo I'm looking at is close to 150K, I assume that JPEG compression was set as low as possible without breaking the 150K rule. A 40K image, however, will get a point detracted, and a comment made because some measure of those artifacts could have been avoided.

It's a learning process, and hopefully, commenting on technical problems which are not necessarily photographic in nature will help improve people's presentation of their own work.

And, for the record... I am pretty freakin' good at identifying these things, but I can make mistakes, so if I incorrectly identified JPEG artifiacts on your photos, I apologize.

Mark


Thank you very much...this is the type of information I was asking for.
09/25/2002 07:52:10 PM · #20
I just tried a test with a photo that I took on my Sony F707. I loaded the image just as it came out of the camera. I saved it from the original 8 times at file sizes between 148k and 30k. To be quite honest, I can't tell a difference in any of them....

Take A Look Here

This introduces several other possibilities.

1- this possibly affects lower resolution cameras more than the higher res cams.

2- using standard jpg mode instead of fine mode may also affect it more...

What else could play a role in this? I'm going to try to take a few sample photos at lower resolutions in standard and fine mode to see what difference it makes....

09/25/2002 07:55:39 PM · #21
That's very interesting, John, the lack of visible difference.

Thanks for your efforts to help us learn. It is greatly appreciated at least by this neophyte.
09/25/2002 08:06:45 PM · #22
I did one more in that folder at 18k and got some artifacting finally...

Artifacts

The original file size was 255k, so 18k is a compression ratio of over 14:1....

09/25/2002 08:11:53 PM · #23
Thanks for the work on that picture John.
For some reason would it be related to that specific pictures ? I mean the fact that we do not see that much difference.
Lionel
09/25/2002 08:21:54 PM · #24
I think it could be... I need to try some testing with a black and white... i think there are probably more differences when there are sharp color contrasts... i will do some more testing with it later...
09/25/2002 08:23:04 PM · #25
However, based on this, I bet we could reduce the max file size at dpc to 125k or even 110k and improve performance for modem users and reduce bandwith usage as well...
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