*** From the Archives ***
This article is from October 21, 2008, and is no longer current.
What’s My Resolution?
First off, I must apologize for not posting at indesignsecrets.com in such a long time. At the beginning of the summer, my wife and I had our second son, Theodore Rocco LoCascio. Since then, it’s been a lot of sleepless nights and extremely busy days as we care for our new little one and our 2 year old son, Enzo. Thankfully, things are starting to get a little easier (only one late night feeding now…yawn), and I now have the time and energy to contribute to my favorite blog site for creative professionals.
A lot has happened during my “maternity leave.” We now have a new and improved site design here at IDS, and we also have a new version of the Creative Suite! How cool is that?
There are a lot of great new features in InDesign CS4, and one that I especially like is the new Link Info section of the Links panel. You can now access a whole bunch of information about a specific link by selecting it in the document or from the Links panel list, and then referring to Link Info.
You can choose which options you’d like to display in the Link Info section by selecting them in the respective Panel Options dialog box. Some of these options include: ICC profile, color space, link path, and layer position. The options that I especially like having quick access to are actual PPI, effective PPI, and scale percentage.
You’ve always been able to access actual PPI and effective PPI readings for a selected link from the Info panel (and still can). However, if you’re like me, and are really bad about referring to the Info panel, then you’ll love the added convenience of being able to determine a scaled image’s resolution right from the Links panel.
The actual PPI reading tells you the resolution of the image at 100%, whereas the effective ppi tells you the resolution of the image when printed at its current scale percentage. Therefore, if you place an image at 100%, then both readings should be the same. Scale the image down and watch the effective ppi value increase.
So let’s say you place an image with an actual ppi reading of 72. At 100% the image resolution would be too low for print. You can tell this by the effective ppi value, which should also be 72. So how far do you need to scale the image down before it’s suitable for high resolution print? Try scaling it down until the effective ppi value is at least 220. When the effective ppi reading is 220 or higher, then you’re safe.
In the old Quark days, I used to calculate resolution by opening my placed images in Photoshop and entering new print size values in the Image Size dialog box, without actually resizing them. This can still be done of course, but why leave InDesign if you don’t have to? And now in CS4 with these ppi values displayed right in the Links panel (which I almost always have open), I always know what my placed image resolution is.
 |
Usually I just enter 24% into the scale input fileds in the control panel, this makes the image 300 dpi.
Of course if you’re not sure what the scale percentage is to take it to 220 dpi, then just divided 72/220*100 which is 32.72% – which you can just type into the scale input field in the control panel.
Of course any knowingly 72 dpi image you’re placing can just be scaled to this percentage. If it’s too big for the page, then scaling it down will increase the effectiveness.
Although if you need it bigger, then you are in trouble.
Where did 220 dpi come from? A few years ago it was 245 dpi, then it was mentioned that it should be 1.5 times the lpi (which is usually 150 lpi * 1.5 = 225 dpi)
Seems the dpi number is shrinking over the years. :)
Great post and I’ve explained this effectiveness ppi vs actual ppi many times to people. I love the way CS4 handles it and can’t wait to get my hands on it.
I use the Info palette. Click on the image with the hollow/white pointer and it will show you the effective and actual ppi, and whether its rgb or cmyk.
Acceptable resolution has definitely dropped over the years. 300 dpi used to be the benchmark, now it is as low as 150 dpi!
Required resolution depends on the image. A ghostly gaussian-blurred image has little detail, so you can get away with 150 ppi or so (something high enough so that the pixels get lost in the halftones). A “high-frequency” image — something with a lot of details in a small amount of space — requires higher resolution.
I have seen the difference between 1.5x- and 2.0xlpi (lpi = the printed halftone screen), but only in high-frequency images. In the vast majority of images, 1.5xlpi is a good amount.
(Technically, 1.414xlpi is probably good enough, as that’s the square root of 2 and should therefore deal with pixels rotated to 45 degrees, but come on… no one wants to multiply by that. ;) )
I just want to reiterate how cool the Links panel is in CS4! It just makes the older links panel look anemic. Seems like a little thing, but it makes a huge difference when dealing with a lot of images.
This feature sounds like exactly what I was looking for, and what everyone should be using! Great!
Ah, David, you know way too much stuff and explain in just the right way. Kudos to you sir.
I like to keep things at 300 dpi anyway, simply because if you’ve got your image as a transparency on the page and your image is at 240 dpi then the High Resolution flattener preset will upsample your image to 300 dpi. And it’s not a very good upsample either.
Unless of course you compensate for this by making a new flattener preset, or of course you change the Spread Flattening Options to Custom from the fly out menu of the Pages Panel.
It’s 300 for me, unless I really really need to make it bigger and I don’t anything else to work with.
I just save (after resizing) everything at 300PPI from Photoshop as TIFF or PSD files, which’ll also help if certain adjustments need to be made as they won’t end up accidentally getting applied to the original files.
Math! Ugh! A designer’s worst nightmare…
David is right. Image contents can make a difference when using lower output resolutions for print. That’s definitely a factor you should consider when placing a detailed image at 100% with effective ppi as low as 150. It would be better to downscale the image until the effective ppi value is above 200. I think everyone’s in agreement that you should never go any lower than 150dpi for high res output.
What the standard value should be for high res output has been a topic of debate for a long time now, but yes, the numbers keep dropping. While I was senior designer at NAPP, our staff was instructed to use 212 dpi as the standard value for high res output. This value was recommended by a “resolution expert,” whose name I don’t recall, but we never experienced a problem putting it into practice. 220ppi was later recommended to me by a printing company I was working with, and that’s what I’ve stuck with as it seems very safe, no matter what the image contents are.
Ha ha Ted. I understand some people cringe at the thought of working something out mathematically, but actually that was one of my first lessons, “stick to the maths and you can’t go wrong”.
Sometimes I deal with a print brokers (print management company) and I send them PDFs. Where they try to preflight the PDF to their settings and it flags images under a certain dpi. So, I get an email saying “there are lo-res images, please fix”, and I look and the effective ppi may be 220 or 240 or 290 or 299.
But this whole hoopla costs time. And I have to ring them, they have to send over sign off sheets saying “I said this image on page x is ok to print”.
I can only imagine the thought that would go through their head if they saw a 150 dpi image.
Eugene-
The upsampling point is an interesting one.
In practice I’ve seen objects that only interact with blend modes or reduced opacity are not upsampled.
Objects that interact with anything in the Effects list (drop shadow, feather, etc), are sometimes resampled to the Gradient and Mesh Resolution for flattened output. There seems to be a threshold that triggers the upsample, but I don’t know what it is. (e.g. a 275 ppi image will not upsample to 300, but a 225 ppi image will). The upsampled regions look lousy onscreen, but I haven’t noticed them in print.
Sounds like you avoid the upsample altogether by keeping everything at 300 ppi. Someone who wants to take their images down to 225 ppi could so the same with a new Flattener Preset with Gradient and Mesh Resolution of 225.
Mike, I just don’t think it’s worth the risk. Nothing worse than getting a print back with low res, or blocky images. Not that it has ever happened, but I do take precautions, but I felt the upsampling was worth mentioning, especially when inserting images as low as 150 – 220 dpi.
And I think I remember someone saying something about making an image transparent at 99% on a page to force the page through a flattening, perhaps for making fonts outline or something? But is this enough to trigger this happening?
I’m not sure, but are upsampled images from the flattner flagged as 300 dpi in preflight? If they are then it’s possible that an image placed at 150 dpi being upsampled to 300 dpi and not being caught by preflighting.
It could be 99.9% transparency, is it enough though to force the upsampling?
Sorry, I wasn’t at my computer to test myself. I am now.
And yes, when you put a 99.9% transparent image @72 dpi it is upsampled to 300 dpi when put through the transparency flattner.
And it breaks up the image in the PDF, so you can actually select different pieces etc.
How can the numbers on resolution output be dropping what would be changing this?
Eugene-
I finally had a minute to confirm your results. You’re 100% right, 72ppi images with only opacity lowered get upsampled to the gradient/mesh resolution.
I think I never noticed that before because there’s that threshold lurking somewhere in there, triggering the resample. The only times I’d have a low res version of an image placed is at an early workflow step when I wouldn’t run any preflight checks, or really care what the proof/PDF looked like.
BTW, a 200ppi version of the same image is not resampled when its opacity is lowered. So the threshold is somewhere between 72?200.
This is fascinating to me and if it hasn’t been covered here already, I’m going to do an investigation/post on it. Thanks.
Good stuff Mike. Good to know there is a threshold, if there was way the user could specify the threshold, then that would be good.
Well I had a friend of mine confirm it for 150 dpi, and he said that is definitely something that he wouldn’t be looking for when creating or checking PDFs.
So, it is a pitfall that should be noted.
I look forward to reading your findings in your investigation.
Oh and I checked in Real World InDesign CS3 book today, and there’s a small paragraph about this on p. 740 (I think). Anyone that doesn’t have this book, GET IT. You won’t regret having this by your side. Although I suspect there’s a Real World InDesign CS4 coming soon?
We are working on RW InDesign CS4, but it’s slow-going.
This resolution upsampling thing is a very good point, but the lesson to be learned is: Make a custom flattener setting that uses 150 ppi for the gradient & mesh resolution! The image is only upsampled when its res is lower than that setting. And no one needs a gradient & mesh setting higher than 150 dpi because this is used for things like feathering and drop shadows (where there is no detail).
David, thanks for the clarification. That is really good information.
I’ve been working on a 3oo page book with around 600 images… I know there are a few images in there that are less than 300pdi, but how do i find them WITHOUT going through them all individually? Is there a way to do this with preflight?
@marc: This is easy in CS4, with the Live Preflight feature. But it’s difficult in earlier versions.
But who cares if an image is 280 dpi? Or 250? That’s still almost certainly enough resolution. The whole “it has to be 300 dpi” thing makes me angry — it’s just such a myth in the industry. 1.5 x your screen frequency is almost always enough. So unless you’re printing artbook 200 lpi screens, I wouldn’t worry about it.
The effective ppi doesn’t show up for my EPS images. Is there a reason why?
Also, I am dropping in eps images (with clipping paths for my silos) instead of psd to save on file size for the catalog I’m working on. Is that necessary or am I missing something? PSDs are so much easier to work with for silos.
Quark has always had the effective resolution information as well. Going back to V8.0 at least