Help! - Compression Problems - DPChallenge Forums

10/24/2005 06:37:48 PM · #1

Alright..

I have redone my entry to the Light on White challenge 4 times now and I cannot for the life of me figure out why I am suddenly seeing the most horrendous compression issues. Big patches are blurry and gross and I don't know why.

I have not done anything I've never done before in a submission and yet I haven't had this problem come up, especially to this extent. The amount seems significant to me, I find it hard to ignore, so does anyone out there have any idea on what it might be that is causing the problem?

I resized to 640 using the Cubic option with Gimp (I usually resize even smaller - 600 - with no problems like this) and my total was something like 123 or 133KB so its on the top end of what is okay.

The ONLY thing I can think of being different is this is a light on white entry so the image itself might seem softer (in general) than others I've taken? Could this have an affect??

Its driving me nuts.

- Sia

10/24/2005 06:38:42 PM · #2

Oh.. and of course it looks great in the original, it doesn't show up until I upload and then all ugliness breaks loose.

>:|

10/24/2005 08:12:36 PM · #3

What software do you use and what steps do you follow to prepare an image for a challenge? Be specific.

10/25/2005 10:17:34 AM · #4

I use Gimp.

If it calls for it I first rotate the image.

I will nearly always then use levels and curves.

Then depending on what I am going for in the image I will use hue/sat and/or bright/contrast.

At this point I will usually save the file as an .xfc which is Gimp's working filetype, similar to saving as a photoshop image in Photoshop so you get little degradation.

Finally I crop the photo (if needed).

Then I resize (using cubic rather than linear) to 600 on the largest side (or in this case I resized to 640 since I was having compression issues) with a 200 dps. *Note* I tried doing a step method of resizing to get from the original 1700 down to the 600 to see if that'd help, it didn't.

Once I've resized I will use some Unsharp Mask. Generally I go Radius: 2.0, Amount: .25, and Threshold: 0. This time I also tried 2.0, .25, and 100 hoping that'd help with my compression problems (it didn't).

After it's been USM'd I will either flatten the image and save as a JPG then upload it..

.. or I will add a border then flatten, etc.

This time I tried with both a border and without, I preferred it without the border.

I use this method pretty much standard - its rare that I follow a different workflow and until this particular image it has served me just fine in the compression department.

10/25/2005 10:21:32 AM · #5

did you have to push the whites heavily due to underexposure?
or did have to do a heavy color cast fix due to improper white balance?

10/25/2005 10:22:03 AM · #6

You said you resize the image to 600 pixels on the largest side, but this one to 640 pix. OK, that's good, but in the next sentence, you say "with a 200 dps." I don't know what this means.

For web viewing, images must be 72 dpi, dots per inch. I don't know what would happen if you had an image that was 200 dpi, but was resized to 640 pix, but I'd think it would display very small.

Double check your workflow to make sure that your 640 pix image is being displayed at 72 dpi before you save as jpeg.

Canon EF-S 55-250mm f/4-5.6 IS

10/25/2005 10:23:37 AM · #7

from what i gather the DPI doesn't matter until you go to print.

BigR

Canon EOS-450D Rebel XSi

10/25/2005 10:26:38 AM · #8

with a 30/30 from 300 yards

10/25/2005 10:30:22 AM · #9

Originally posted by BigR:

with a 30/30 from 300 yards

Hmmm, wrong thread?

10/25/2005 10:53:03 AM · #10

Whoops. When I said dps, I meant dpi I believe.

Resolution I always change to 200 simply because its my habit for all challenges (and my prints) and usually I'm working with an even smaller image (600) and there haven't been any problems until this image.

In levels I moved the white slider to the left by .15 and the grey slider by .15 and in Bright/Contrast I upp'd the contrast by.. 20 I think and Brightness maybe by 10.

I just now did a test to see if those adjustments have much to do with it by taking the original and simply cropping it down to where I did on my entry, resizing and then USM and uploading and the same compression issues still arise.

Could it be an effect of my cropping? I am removing a fair amount to get the composition I'm looking for, maybe this is where my troubles are starting.

10/25/2005 11:03:15 AM · #11

Any image you upload to a website is going to be displayed at 72dpi. You said that you are specifying 200 dpi in your workflow, and your image looks fine to you on your computer, but after you upload and look at it on DPC, you see the artifacts. My guess is that you saving the file at 200 dpi is the problem. Does GIMP have a feature that is analogous to Photoshop's "save for web" feature? If so, try that. If not, crop your image down to 640pix on the longest side, and make sure that resolution is set to 72dpi, and then save as jpg. You might need to tweak the compression to make sure it's under the 150k size limit.

Hopefully some other GIMP experts will weigh in here too.

10/25/2005 11:15:30 AM · #12

That's correct, all images I've uploaded for challenges (and for DCPrints) for the last year or so have used a 200dpi.

This is the first time that I can recall having this bad of an artifact problem AFTER uploading to DPC. All other times the 200dpi choice has held up wonderfully both on my computer and after its been uploaded to a challenge/the site.

That said, I did try uploading with the standard 72dpi. I didn't see a difference. Maybe this particular image is simply jinxed. :)

I have looked for a "save for web" option since I've seen others mention using this route as well, but so far I haven't been able to find anything.

10/25/2005 11:53:36 AM · #13

I'm stumped. I have a feeling it's something so obvious it's easy to overlook but I don't know what that might be, not being a GIMPer. I looked at your other challenge entries and you obviously have it down, but something mysterious is jinxing your current image.

If you post a new thread with GIMP in the title, you'll bring those folks out of the woodwork. Or better, contact and SC and get them to add the word GIMP to the title of this thread.

Good luck!

10/25/2005 12:21:26 PM · #14

this isn't an issue...

Originally posted by strangeghost:

10/25/2005 12:22:47 PM · #15

../

Message edited by author 2005-10-25 12:43:45.

Prof_Fate

10/25/2005 12:27:13 PM · #16

On your computer are you viewing it at 100%? I notice moire at times on pics unless i view them at 100%. and ov course, vieing at a higher magnification will show isssues that are not really there.

It may help to downsize it in steps, as in 75% of the original, then 75% again, etc until you get to the 600 you want. The difference is subtle, but there is a difference.