Cropping and resolution

[scottleslie]

I have some experience with digital photography, from exposure to .jpg to PhotoShop CS to print (and one show) but have recently moved up to a D70, CS2, and RAW format. I'm finding the resolution part of the learning curve more daunting than the rest (which is considerable).

I'd always heard (read) that it's best not to resample, but to manipulate pixels per inch to resize the image without PhotoShop's messing with the pixels as exposed. That's fine for printing out the shot as shot, but in the real world where I come from most photos are cropped for artistic reasons. What's the optimum method to crop without altering the image's resolution more than absolutely necessary?

My current approach: open an .nef file, 3008 x 2000 @ 300 ppi,  select the crop tool and delete any numbers in the Width, Height and Resolution boxes, and then, using the Info window lower-right as a guide, select a 4x5 inch area (assuming I'm aiming for an 8x10 print).

Then I Shift-drag a corner of the crop area and move the whole thing around until it's covering what I want, and hit Enter (PC). Image Size tells me that it's now 5.587 in by 4.45 inches at 300 ppi (in this case—depending on how the crop area is dragged it could be any size, but the ratio is 8x10).

Two more steps: 1) Turn off Resample in Image Size and experiment with Resolution until the Weight and Height come out right; in this case 166 gives me 10.096 by 8.042, close enough. But 166 is too low for printing on an inkjet, so 2) I turn Resample back on and simply double the 166, to 332. PhotoShop is now doing what photographers more experienced than I seem to hate: stuffing pixels in between the original ones. But at least it should be an optimally even process, with minimal artifacts; at least, that's the way I'm figuring it.

Does this make sense to anyone? Or is there a whole lot simpler way to crop (or resize, for that matter) without messing more than absolutely necessary with the pixels as delivered by the camera?

Scott Leslie
Point Reyes, California

[francois]

I have some experience with digital photography, from exposure to .jpg to PhotoShop CS to print (and one show) but have recently moved up to a D70, CS2, and RAW format. I'm finding the resolution part of the learning curve more daunting than the rest (which is considerable).

I'd always heard (read) that it's best not to resample, but to manipulate pixels per inch to resize the image without PhotoShop's messing with the pixels as exposed. That's fine for printing out the shot as shot, but in the real world where I come from most photos are cropped for artistic reasons. What's the optimum method to crop without altering the image's resolution more than absolutely necessary?

My current approach: open an .nef file, 3008 x 2000 @ 300 ppi,  select the crop tool and delete any numbers in the Width, Height and Resolution boxes, and then, using the Info window lower-right as a guide, select a 4x5 inch area (assuming I'm aiming for an 8x10 print).

Then I Shift-drag a corner of the crop area and move the whole thing around until it's covering what I want, and hit Enter (PC). Image Size tells me that it's now 5.587 in by 4.45 inches at 300 ppi (in this case—depending on how the crop area is dragged it could be any size, but the ratio is 8x10).

Two more steps: 1) Turn off Resample in Image Size and experiment with Resolution until the Weight and Height come out right; in this case 166 gives me 10.096 by 8.042, close enough. But 166 is too low for printing on an inkjet, so 2) I turn Resample back on and simply double the 166, to 332. PhotoShop is now doing what photographers more experienced than I seem to hate: stuffing pixels in between the original ones. But at least it should be an optimally even process, with minimal artifacts; at least, that's the way I'm figuring it.

Does this make sense to anyone? Or is there a whole lot simpler way to crop (or resize, for that matter) without messing more than absolutely necessary with the pixels as delivered by the camera?

Scott Leslie
Point Reyes, California
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Scott,
Have you read Michael's article about resolution ([a href=\"http://luminous-landscape.com/tutorials/understanding-series/und_resolution.shtml]here[/url])?

[Nill Toulme]

...Does this make sense to anyone? Or is there a whole lot simpler way to crop (or resize, for that matter) without messing more than absolutely necessary with the pixels as delivered by the camera?
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As for cropping, yes, simply set your crop ratio, e.g., 4:5, in the Width and Height fields of the crop tool and make sure the Resolution field is blank.  Then just drag to make your crop.  Move it by dragging inside the crop; adjust its size by grabbing the corners; rotate it by clicking and dragging outside the crop; apply it by hitting Enter or by double-clicking inside the crop.

As for resizing, well, no, you can't literally resize the image without changing the number of pixels; that's pretty much by definition, isn't it?  Or do I misunderstand that part of your question.  You can change the resolution of the image without changing the number of pixels, e.g., you can change it from, say, 4" x 6" at 300 dpi to 8" by 12" at 150dpi, but that's really just a form of tagging or labeling — you're not actually changing the image itself at all.  You do this by changing the image size (Image/Image Size) with Resample Image unchecked.

There's little point in doing this however, as your printer driver is going to literally resize the image when it receives it anyway, unless you happen to send it the image at its own native resolution.  That's kind of off on a different topic, though.

Nill
~~
[a href=\"http://www.toulme.net]www.toulme.net[/url]

[scottleslie]

Scott,
Have you read Michael's article about resolution (here)?
[a href=\"index.php?act=findpost&pid=93439\"][{POST_SNAPBACK}][/a]

Yes, I have. He states that resampling "in moderation" to bump up a photo's size gives satisfactory results, but he gives little in the way of guidelines. I guess that's what I was looking for.

By way of the example I gave, if I double resolution, and therefore size, is that too much?

[scottleslie]

As for resizing, well, no, you can't literally resize the image without changing the number of pixels; that's pretty much by definition, isn't it? 
Nill
~~
www.toulme.net
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I guess I was looking for guidelines on that. Thanks for the reply.

Scott

[Nill Toulme]

I guess I was looking for guidelines on that. Thanks for the reply.
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Ah, OK.  As of CS2, PS's interpolation routines are as good as most of the third-party stuff available, and there's no need to do the old 10% stairstep approach either.  In other words, when you need to upsize, just do it using Image/Image Size, with Resample Image turned on and set to either Bicubic or, for some images and very large increases, try Bicubic Smoother.

As a general proposition, you'll get the best results printing if you do your final sharpening *after* upsizing to final print resolution, and you'll also do well to make that final resolution at, or at an even multiple of, the printer's own native resolution.  For Epson printers this means 360ppi, for most others 300ppi.  For example, if you're going to print an 8x10 on an Epson printer, do all your other processing including initial capture sharpening and any additional "creative" sharpening you might want to do, then resize the image to 8x10 at 360ppi, then do final print sharpening, and print.  [a href=\"http://www.pixelgenius.com/sharpener/index.html]PK Sharpener[/url] is an excellent tool for these various sharpening steps, BTW.

Or you could make your life a lot simpler and just get Qimage.  It does all the resizing, print layout and print sharpening for you, quickly and easily, and IMO does a better job than PS, or at least a better job than I myself can do with PS.

Nill
~~
www.toulme.net

[scottleslie]

Ah, OK.  As of CS2, PS's interpolation routines are as good as most of the third-party stuff available...

Nill
~~
www.toulme.net
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Ah, thanks. That's a bunch of sound-sounding advice. I shall pursue it.

Scott