Digital image manipulation

[taimatsu]

Am trying to understand image resolution in Photoshop.

I am producing a book cover at a specific print size - 18.1 cm x 11.1 cm. The resolution should be 300dpi if at all possible, with an absolute minimum of 150dpi.

I have created a canvas in Photoshop with the right cm dimensions and resolution, and I have pasted my photo into it. The photo fits, which is fine, but really I want to resize the photo to focus on a section of it. If I select an area and make it bigger won't I make it look pixellated when it prints?

Can anyone help me get my head round this?

Comments

[brrm.livejournal.com]

Unless I've confused myself, it will be more pixellated than if you hadn't blown it up, but you won't be losing any pixels from the photo, IYSWIM - i.e. you're just making them bigger.

[martling.livejournal.com]

If your photo is on the canvas at 300dpi then you can safely zoom in by a factor of two and still be at 150dpi.

[ewx.livejournal.com]

If you enlarge it too much then yes, it'll start to look bad. How much is "too much" depends on the resolution of the original image.

[simont]

You should probably paste your resized area direct from the original photo rather than the version you've already pasted into your Photoshop canvas, on the grounds that either the version in the canvas will probably have been reduced in resolution (so that it looks unnecessarily coarse when you enlarge again), or have been enlarged already (so that you get slight additional fuzziness from double enlargement).

It may still look pixellated if there really were not enough pixels in the original image to adequately cover the area you want, but if so then that's unavoidable. All you can really do is to avoid avoidable pixellation caused by reducing an image's resolution and then re-enlarging.

(I hope I've got the right idea about what you're trying to do.)

Generally when I'm doing raster image manipulation I try very hard to avoid thinking in physical measurements at all unless absolutely necessary: think entirely in terms of pixels, and then "size" and "resolution" become identical concepts so you don't have to think about them separately :-) I appreciate that in this case you have some need to think in cm in order to get the photo the right final size on the page, but if it were me I'd convert that size into pixels right at the start of the process and not think about cm thereafter until it was printed and I was measuring it to make sure it came out right.

[doctor-frank.livejournal.com]

Generally when I'm doing raster image manipulation I try very hard to avoid thinking in physical measurements at all unless absolutely necessary: think entirely in terms of pixels, and then "size" and "resolution" become identical concepts so you don't have to think about them separately :-)
This is good advice :) Thinking about pixels is much, much easier.

What's the pixel size of the page compared to the pixel size of the image?

[sea-cucumber.livejournal.com]

Depends what resolution the photo was in when it was scanned in or what resolution it came out of from the camera if it's digital, if the original is more than 300dpi you can make it bigger accordingly with no loss of quality...

[undyingking.livejournal.com]

won't I make it look pixellated when it prints

Yes. Although if the photo is in high enough resolution to begin with, maybe not noticeably so.

Best practice is to (a) work out exactly how many x * y pixels you want the part of the iamge you're using to end up, (b) crop out the part of it you want before pasting it into anything, so you can (c) resize that part as required, and then be (d) doing all your image-assembly at the right size.

Other things to note -- (a) if it's a jpg, be sure to save any internediaries at no compression, as otherwise you might find yorself inadvertently applying compression repeatedly which will create nasty artefacts, and (b) it's better to resize in exact simple multiples if you can, to avoid moiré effects.

[bateleur.livejournal.com]

Another relevant point which nobody seems to have noted yet: when Photoshop enlarges things it actually does better than just scaling them up. As such, your image is more likely to blur very slightly than look pixellated for small levels of enlargement.

How bad this looks depends on the image. Some pictures will happily handle a 400% scaling without looking bad.

[randomchris.livejournal.com]

Depends on the size of the section that you want to blow up. Cut it out of the original photo and check its dimensions in pixels, then compare it to the minimum number of pixels that you've got to have for the correct size at 150dpi. If it's below the minimum, you'll definitely get some pixellation; if it's above it by a factor of 2, then there shouldn't be noticeable pixellation; in between, there might be a little.

[spaglet.livejournal.com]

Just to confuse you further: it won't look pixellated, as such, until it's very big relative to its original size, but it will look coarser. When you make it bigger, Photoshop will resample it with a reasonable filter rather than merely duplicating pixels to make it to the size you've asked for.

This will tell you many things you didn't think to ask about (http://www.amazon.com/Real-World-Scanning-Halftones-3rd). One is that dots per inch is a terrible measure unless you know exactly what your printer is doing, and even then it's suspect. ;)

[lovingboth]

Ah, beaten to posting about that book.

[rits-ka.livejournal.com]

oh lol.. so complicated.. i wish u cope with it..

[haggis.livejournal.com]

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[taimatsu]

Yay! Poing! and suchlike excitable noises :)