Help with zooming and sharpening

[jwg1800]

I hope this is the right area of the forum. I'm using photoshop cs and I'm a total newbie. I have several jpeg images of products for a new website and I want to enlarge them. Also most of them need to be rotated about 45 degrees. I've found that some distortion occurs when I rotate arbitrarily and there's definitely distortion when I enlarge the image. I'm assuming the best tool to use to fix this is the unmask sharp tool. Can anyone give me some tips or pointers on this tool or any other tools that might be helpful after I rotate and enlarge my images?

Thank you,
John

[Doug Nelson]

Enlarging from a JPG is hard because JPG (by definition) tosses out a lot of image information to compact the file size. There are some 3rd-party apps that might help with this (someone might be kind enough to recommend some), but I'd recommend simple stair interpolation. Increase the size 10% at a time using bicubic resampling (or bicubic sharper if you have PScs). Resize first, then rotate for best results. And don't rotate more than once, each time is destructive.

Good luck!

[jwg1800]

Thank you for the quick reply. Might I have better results if I first changed the image to a tiff file and then did the resizing and rotating? Also can you explain more about "stair interpolation". Thanks again.

John

[Doug Nelson]

Changing to TIF (or PSD) will prevent further degradation. They are "lossless" formats (as opposed to JPG). You can then export to JPG should you ever need that file format.

"Stair" simply refers to doing it in steps, instead of all at once. And interpolation means it guesses what the new pixels should look like (since that's essentially what enlarging is doing, adding pixels).

[jwg1800]

gotta, appreciate your suggestions. If anyone else has anymore, their definitely welcome here

John

[edgework]

JPEGs work by using a pre-coded set of B&W patterns for detail. Each pattern is an 8x8 pixel grid. That's why, when you zoom in on a JPEG image, particularly one that is low-res to start with, you see those blocky artifacts. When you save with higher quality, multiple patterns are "layered" and combined to simulate the detail from the original image, and a high resolution file saved at highest quality can be difficult to tell from the original. That's why a JPEG that is resaved as a JPEG degrades beyond recognition. It's like recording a audio tape with a microphone off a radio speaker.

The only thing that really matters is the actual size of the image in pixels before it is JPEGed. The greater the pixel depth, the less significant an 8x8 pixel block will be in relation to the whole. But an image that is, say, 4x5 to start with, at 72 dpi resolution, saved with high compression (low quality) will require some creative solutions. Abstracting the image by blurring, adding noise, grain or using the diffuse filter can create interesting results that hide the artifacts, but which move a fair distance away from realism. I've also had some luck actually cloning out the obvious artifacts in areas between light and dark regions.

The best solution is to plan ahead and make sure your images start out as hi-res. Much easier to down sample later.

[jwg1800]

edgework,

thanks for your reply. I don't really know how to do any of the stuff you were talking about, not sure if I said earlier but I'm a newbie. As for starting out with hi-res, I wish I had the option, but the images that I'm having trouble with here are downloaded from the internet from a wholesaler that I buy from.

John

[Ed_L]

Originally Posted by jwg1800

I've found that some distortion occurs when I rotate arbitrarily and there's definitely distortion when I enlarge the image.

What I have to say is something that is not likely to be part of the problem, but it *is* a possibility. I have only noticed this very few times. On very rare occasions I have noticed distortion (eyes slightly misplaced, nose too large, etc.) when viewing a file at other than 100%. But this is only distorted on the monitor. In other words, if I printed the image, it would not be distorted even though it looked that way on the monitor. I never did find out what causes the apparent distortion, and it is very rarely noticed.

Ed

[byRo]

As you are using in Internet image, probably you're going to want enlarge it more than just a couple of 110% steps.
If you are making a 2x enlargement (or more), you can try going direct: Image Size > Width 200%, Constrain Proportions, Resample Image Nearest Neighbor

In normal photo retouching you wouldn't do this. But in this case you're probably working way below the borderline for pixel size, so the (cost of the) blurring introduced by a number of 110% steps may outweigh the (benefit of) enlargement.

A 110% step after the 2x Nearest neighbor helps tame the 'jaggies'. So you could get to 220% total with a decent image.

If that's what you need - it's worth a try.

Good luck,

Roland

[Gary Richardson]

Hi Ed, the only Zoom ratio at which there is no distortion to the image on screen is 100%, at all other times Photoshop is doing an interpolation of your pixels to display your image. At ratios like 50%, 25%, 200%, the interpolation is simple and minimum distortion of your image occurs, but if you use the popular "Fit on screen" command, the zoom ratio can be anything, therefore the interpolation is more difficult, and sometimes distortion is quite noticeable. As you have'nt actually changed any pixels, naturally there is no distortion to the actual image, and it will print OK.