Artifacts
Apologies in advance that this post gets a little bit specific and technical. I'm blogging this on the off-chance that some PhotoShop genius wanders this way!
I need advice with a rather strange PhotoShop problem. It's not particularly important, it's just bugging me.
Earlier today, I took this picture with my new camera:
Which I kinda liked, so I wanted to have it as a desktop pattern. I loaded it into Photoshop, and resized it to 1024 pixels in height, to fit the height of my screen. It looked good, but the blurred areas around the stems appeared to have a slight but noticeable mosaic effect.
At first I thought I'd accidentally turned off re-sampling when I resized the image, or some other basic setting. But everything appears to be fine.
Here's a close-up of the effect, I've added two "sharpen more" filters to emphasize it a lot more:
See the mosaic pattern?
Compare to the following picture has exactly the same processing done to it, but I resized to 1152 px height (exactly 50% of the original).
No resampling artifacts! In fact I think they only occur when the resampling is around the 1024 pixel high range (or about 44.44% of the original size).
Has anyone else who uses PhotoShop come across this?
I need advice with a rather strange PhotoShop problem. It's not particularly important, it's just bugging me.
Earlier today, I took this picture with my new camera:
Which I kinda liked, so I wanted to have it as a desktop pattern. I loaded it into Photoshop, and resized it to 1024 pixels in height, to fit the height of my screen. It looked good, but the blurred areas around the stems appeared to have a slight but noticeable mosaic effect.
At first I thought I'd accidentally turned off re-sampling when I resized the image, or some other basic setting. But everything appears to be fine.
Here's a close-up of the effect, I've added two "sharpen more" filters to emphasize it a lot more:
See the mosaic pattern?
Compare to the following picture has exactly the same processing done to it, but I resized to 1152 px height (exactly 50% of the original).
No resampling artifacts! In fact I think they only occur when the resampling is around the 1024 pixel high range (or about 44.44% of the original size).
Has anyone else who uses PhotoShop come across this?
April, the intense shapening was deliberately added by me in PhotoShop. Like I said in the posting, I used two "sharpen more" filters to make the mosaic effect I could see more noticeable in the samples I gave.
I agree, it's a bad idea to do any sharpening pre-processing on the camera. I wouldn't have even touched the sharpen button in this case if I didn't want to highlight the effect. I'm not that much of an amateur. ;-)
hmmm...what version of photoshop are you using? Curious that you are getting the same effect on control images. I found the hi-res orig on flickr and checked the EXIF. ACDSee reports Contrast, Saturation and Sharpening are all set to high - which I think is the default setting for the 300D, so I would imagine that it would be the same for the 350D - but you state this is not a camera problem. Unless my software is reporting wrong. However I looked at the image close up and also resized it and couldn't find any blocking issues apart from slight chromatic abberation which is to be expected and well within limits. Do you get the same issues if you convert original to TIFF and then work on it and export to .bmp for desktop?
oooh - a techie mystery - I love it.
Okay, I downloaded the original from Flickr, resized it with constrain proportions on so it turned to 1536x1024. Then I tried a few other times with the resample image on different settings (nearest neighbor, bilinear, bicubic), and well... I don't see it that bad. I don't know if it's my monitor or I'm blind or your original is 300 pixels/inch and the one I'm using from flickr is 72 pixels/inch or what... If I take the original photo, and use the magnify tool and demagnify it once so it's at 66.7%, i can see the mosaic. SO, here's a crazy idea, if sharpen makes it more obvious, why not blur it just a little until the mosiac goes away? :)
(What?! I teach this sort of stuff. Sod off :p)
The only way I could reproduce the mosaic effect you're showing here, is if I set the resampling in the "Image Size..." dialogue box to "Bilinear". Bilinear isn't good - it's a half-way house between the sumptiousness of "Bicubic", and the quick-and-dirtyness of "Nearest Neighbour". Bicubic samples all the pixels around a pixel to determin its new value, whereas bilinear only samples the ones above and to the left and right of it. It was great in the old days to be able to resize stuff reasonably quickly and reasonably accurately using Bilinear considering we didn't have the processing power we have today. But honestly, if you're resizing something, stick to Bicubic. And perhaps experiment with CS's new "Bicubic Sharper" and "Bicubic Smoother".
This doesn't apply to resizing video BTW - it seems that sizing stuff down in video works out a lot better if you use Bilinear.
Personally, I always use Bisexual resizing. You get the best of both worlds...
Thanks for having a play!
If nothing else this post has taught me to be very detailed when describing Photoshop issues! Otherwise people assume stupidity. ;-)
I was using bicubic, bilinear is naff. It was one of the first things I checked, cos it looked like nearest-neihbour nastiness. Gah, April talking down to me about cameras and now you talking down to me about PhotoShop!
(Kidding, I know you two were talking lowest-common-denominator to make it general advice rather than specific to me.) :-)
I don't take it personally. [lip quivers]
I think this must be an effect that's very specific: any reasonably blurred picture in Photoshop V7 that's resized down to 44% size using bicubic resampling (or worse) will get that effect. The resampling in CS or later must be more effective cos it doesn't appear to do it.
I need to upgrade my PhotoShop. :-)
No, take it personally. We both think you're an idiot :)
I ran into a similar situation at a company that used Photoshop CS1 for making tradeshow graphics.
One phenomenon we ran into was similar to what you described if you try and increase the image size "too much" in one operation. The solution they came up with was to set the image resolution first and then resize the image 105% at a time repeatedly. This was done with bicubic interpolation and constrained proportions.
This worked out pretty well at increasing the photo size without introducing a lot of unwanted pixellations! This can make for some really big files though, so you will want to do a "save for web" to keep things reasonable!
And setting that operation up as an action saves a lot time! Good luck!
SMSapphire
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