pixelization

paulhenri · Posted: Thu Apr 17, 2008 10:36 am Post subject: pixelization

why would pixelization occur at "Fit to Screen" size for an image that is approx. 6 x 9 and not when this same image is enlarged to 100%? it also appears as if every other click of the magnifying glass will create pixelization and every other looks very clean and crisp. My wife is concerned about submitting images for publications, etc. that appear to be not crisp at "Fit to Screen" size. I have a CRT Dell monitor about 3 years old. Any ideas on this and what can be done if anything to correct this? Also, she is a clay sculptor it appears as if the images that have a lighter finish to them against a darker background are more likely to have this issue than the darker finished pieces of artwork. see attached

Matt · VIP

Hey paulhenri,

It's all to do with how Photoshop renders the screen preview, nothing to do with what the image really looks like!

When you're viewing the image at a view size of 100%, photoshop is using 1 screen pixel to represent 1 image pixel - giving you the most accurate view of image possible. If you zoom out to an irregular zoom ratio then Photoshop has to chop and change pixels around in order to preview them. Unfortunately the interpolation used for this process is a very basic average of pixels that need displaying so you'll notice that at 66% you get jagged edges and harsh transitions - the same goes at 33%, 47%, 86% etc.

The fit to screen view ratio is dependant on the size of the image and the size of your monitor, so usually you'll end up viewing the image at a problematic zoom ratio. I'd always reccommend using a view ratio of 100%, 50% or 25% for these reasons!

Hope this helps

paulhenri · Posted: Thu Apr 17, 2008 3:28 pm Post subject:

Matt, thanks for your time. One thing I didn't mention is that it does not happen with all the images of her work. Mainly with the ones that have a lighter finsih. The darker ones do not show up this pixelated at Fit to Screen size.

why would there be this difference between the lighter ones and the darker ones?

Thanks,

Paul

Matt · VIP

What format are you shooting to? And are you doing any processing before you bring them to Photoshop? I ask this because the issues around the shoulders looks like compression artifacts to me.

Another question while I'm asking lol, are you resampling the image inside Photoshop using the image size command?

paulhenri · Posted: Thu Apr 17, 2008 4:34 pm Post subject:

I shoot everything in Raw-Canon 20D, strobe lights for these types of things. Usually do not do anything in Raw except write them out as Tiff's which is where I do all my PS work, them save them and save them again as Jpeg's for printing purposes.

As far as resizing, sometimes I resize as I write them out from Raw. They are usually sized to original size of something like 10.019 x 6.679 or whatever, I don't exactly remember, but I size them out at 6 x 9 on their way to Tiffdom. And again, sometimes I resize them when I get them into PS because I don't always remember to do it on the way out of Raw, but I never size up from there on my system. Not sure what exactly compression artifacts means-can you explain a bit for me. I appreciate your time.

PH

Matt · VIP

Sounds fine.
The image preview problems will be amplified by areas of high contrast in a photograph, things like a light foreground against a dark background! On a photograph where you notice this occurs, set the view size to 100% and see if it's still a problem.

As far as compression artifacts go, you'll find an image saved into a lossy format (such as JPEG) will suffer from banding when saving with lots of compression - you won't get this with raw or tiff.

On a side note, I'd suggest you try to cut the conversion to JPEG completely out of your workflow if you can. You can use Camera Raw to colour adjust raw images, and if you need to go to tiff, you should be able to print things without converting to JPEG.

Let me know how you get on with the 100% view size?

paulhenri · Posted: Thu Apr 17, 2008 5:03 pm Post subject:

Matt, I really appreciate your help. 100% always looks perfect. But my wife is very particular about how her stuff looks and I needed a good reason to explain to her that at Fit to Screen is not a good representation of the image, so I am copying all your replies to show her. And the only reason I write out to Jpeg is because I do not do my own printing and I send them out via a local print bureau that only accepts Jpegs to their site. As I think about it, the images that she first noticed this jiggedyjaggedy edge was in fact a Tiff file because we were still working on it. And finally, all of these images when printed to 4 x 6 looked fine, and even the ones that we had printed to 6 x 9 loooked fine. I print many of my own photographs at 11 x 17 and they look fine as well.

thanks again,

Matt · VIP

No problems,
Yes if the image looks good at 100% the problem definitely resides with how Photoshop renders the image preview. If you enter the Image Size dialogue box you'll be able to see the 5 resampling methods for when you're actually resizing an image. When Photoshop resamples on-the-fly for viewing purposes it uses the nearest neighbor algorithm - definitely the worst to use for photographic images but because it's only providing you with a screen preview, it uses nearest neighbour for its mathematical simplicity. Instead of averaging 8 pixels for every 1 it previews, you end up with a duplication of 1 pixel which is why things can look jagged and lumpy.

Let me know if you need any more info

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