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DPChallenge Forums >> Challenge Results >> Post Processing Question - Newbie
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 12/08/2006 03:00:50 PM · #1
So i entered my third challenge and first Free Study! I wasn't expecting a great score as the results weren't what i had hoped;



I'm pleased with the medium score which indicates the picture wasn't bad (hell I got a 10 vote!) and I got some great comments. Now I'm looking for some advise for improving my next entry. The pic turned out quite noisy and I'm not sure why. I shot with ISO 50 so thought it would be less "grainy" looking. One commenter said that I compressed it 3x more than needed as the file was only 50KB. I don't know what I did wrong. Here was my process as best I remember: The orig was 2448x3264 and 1,376KB. I cropped out about 1/3 of the original, adjusted colors and contrast a little bit, added a border, resized to max 640 pixels, processed with Unsharp Mask, (using Paintshop Pro XI) then uploaded to DPC.

Can someone recommend what I might have done to improve the quality of this entry? I recently got Paintshop Pro XI and trying to learn how to use it. I consider myself an "OK" photographer with a fair eye for componsition but I'm really a duffous when it comes to Post Processing. I would love to get some good advice or links to good learning sites out there (preferrably using PSP).

Thanks for any helpful comments you can offer.

Carlos
 12/09/2006 07:25:52 PM · #2
I'm guessing the high JPEG compression is the main culprit for the grainyness. There must have been some noise there in the first place (which I agree is strange at ISO 50), but then it got amplified by the greater-than-necessary compression. The story on JPEG compression is simple: it's evil and you want as little of it as possible. Since you have to get filesize below 150KB for DPC, pick the amount of compression that gives you a filesize just below 150KB. If the file is much smaller (like in this case), you've unnecessarily hurt image quality.

I don't know how this is done in PSP, but in Photoshop you get an option to choose target file size inside the "Save For the Web" dialog. If I set that at 148KB and JPEG compression, I get anything from 75% to 99% image quality, depending on image complexity, amount of noise, etc. If you have to manually pick the image quality in PSP, try 90% first and see what filesize that gives you. Also make sure you are saving the file without any thumbnails or previews since they just waste file space when you are uploading to the Web.

Finally, noise is really hard to compress, so unless you are deliberately going for a noisy look, you can often improve image quality by removing some of the noise. As I mentioned in my comment, with this image you could select the sky (in Photoshop you'd use the "Magic Wand" selection tool) and then blur it with a large radius (say 50) Gaussian kernel. Or you could buy Noise Ninja or Neatimage which remove noise automatically.
 12/09/2006 07:31:20 PM · #3
Originally posted by magnus:
I'm guessing the high JPEG compression is the main culprit for the grainyness.


Looks a lot like compression artifacting.
 12/09/2006 08:54:58 PM · #4
In PSP, I chose Resize which is a dropdown from the Image menu. Here you can choose to resize by pixel dimensions or print size. I kept the aspect ratio locked, and just reduced the larger pixel block (width or Height) till is was 640. I don't see any quality settings, but there is a Resample Using: dialog box and drop down choices of:

Smart Size
Bicubic
Bilinear
Pixel Resize
Weighted Average

I'm not sure what the differences are between these. I believe I just went with the default which is Bicubic. I just did a little searching through the help file and this is what they recommend... although nothing is said about quality of the picture.

Thanks for the help!

12/10/2006 02:53:05 PM · #5
JPEG compression is different to what happens during a resize operation - JPEG compression happens when you save the file. When you resize in PSP, it uses one of the methods (Bicubic, Bilinear, etc) to work out how the resized picture should look - so far all good. When you go to save the resized picture as a JPEG, the JPEG algorithm compresses the resulting file. More compression makes for a smaller file but it looks progressively worse.

Photoshop gives you a slider-bar during a save, so you can trade off quality vs size - the general objective should be to get a close under 150kb as you can, as this'll result in the best image :)

Hope this helps !
 12/10/2006 06:13:06 PM · #6
Hey thanks... i just learned something new! I opened a file in PSP and selected Save As: there's an Options button that allows you to slide from 1-99 (lowest compression, best quality - highest compression, lowest quality). I didn't realize that was there before. It seems that it was defaulted to 20. Given the size of pictures displayed on DPC, is there a point of dimenishing return where the improved quality wouldn't be seen but the file size would get too large?
 12/10/2006 06:54:55 PM · #7
Originally posted by carlosm:
Given the size of pictures displayed on DPC, is there a point of dimenishing return where the improved quality wouldn't be seen but the file size would get too large?


Try testing it out, but personally I'd head for somewhere over 75%. Within the 75-100% range there's sometimes not much to see between them, below 75% quality it seems to drop off rapidly and become blocky or have really obvious colour transitions across gradients.

Also FWIW if you use the "save for web" option instead of Save As for challenge entries, then the Exif data will get stripped out and you can specify a file size which will show the percentage quality, from which you can determine if you need to make the shot a bit smaller.

Message edited by author 2006-12-10 18:56:10.
 12/10/2006 07:56:56 PM · #8
more good advice... thanks! I don't know if there's a way to check but i'm assuming that the picture was saved with the setting I mentioned (20)as this apppears to be the default. This being the case, it was already 80% and resulted in grain. I'll have to play around it and see what results. Paintshop Pro doesn't appear to have a "save as web.." option that i've been able to find. The Save As: dialog box gives you the option to strip the EXIF. It also gives three choices of Encoding Type: Standard, Progressive and Lossless. If you choose Lossless, the slide bar for choosing compression factor is greyed out so I'm assuming this is the same as compression factor 1, ie. best quality. Unfortunately, it appears that you can't tell what the file size is until you save and then look at the properties.
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