Just exactly what do you want to do with these files? Once we’ve got that info, we’ll be in a much better position to offer advice.
Bob
Image>Image Size should do the trick.
Suppose you have a photo that was scanned at 8.5×11, at 300dpi, but you only want to print wallet size pics (roughly 2.3×3)
In the Image size dialog, with "Resample Image" UNchecked, change the Print Size to what you want at the end. In this example, changing the Print size from 8.5×11 to 2.3×3 caused the resolution to jump from 300 to 1108. Now, CHECK the Resample Image box, and change the resolution to 300 at the new size.
The final pixel size in the example changes from 2550×3300 to 690×893.
As a final step, you may wish to apply Unsharp mask to sharpen the details.
You can do all this to the PSD file. No need to change the format to JPG.
Loss of quality comes from 2 places: file compression (used by the JPG format) and insufficient data (fewer pixels per inch than required for output). For output, 300ppi is more than adequate for almost any high-quality print job, and 72-96ppi is appropriate for screen resolution (images to be viewed on the web). Using Save for Web or saving the file as a JPG will not reduce the number of pixels in your image; it will apply compression to your file. Always start by using the appropriate number of pixels for your output. If further space savings is required, then start using compression.
Sorry for the super-detailed directions, if you already knew all this stuff.
72-96ppi is appropriate for screen resolution (images to be viewed on the web).
A small correction to Susan’s excellent post. Resolution is ignored when an image is displayed on the monitor. The monitor just displays pixels and the resolution is fixed to the resolution of the monitor. So image resolution is totally irrelevant for monitor/web images.
bert
Bert
I disagree. Resolution is irrelevent for web display, but it is very relevent in producing images, and Susan is correct in saying that 72-96 ppi is appropriate for producing images that will be displayed on the screen, while 300 is more appropriate for those that will be printed.
I disagree. Resolution is irrelevent for web display, but it is very
relevent in producing images, and Susan is correct in saying that 72-96 ppi is appropriate for producing images that will be displayed on the screen, while 300 is more appropriate for those that will be printed.
Huh? Web display IS "displayed on the screen". If resolution is irrelevant for web display (which it is), then it is also irrelevant for displaying images on the screen. Bert is correct.
Don,
As far as I know, no image display package looks at the resolution tag. Some will resample the image if it is too big (too many pixels) to fit on the screen, but most just put it up with scroll bars. Both types completely ignore the resolution tag. If you know of an image viewer that looks at resolution, please tell us.
Bert
Quentin,
I have a few images that were originally scanned at much too high a level of detail… I want to reduce them in size without degrading the quality of the images noticeably.
You didn’t make it clear whether you also want to have the opportunity to make large prints from these images at a later time. If that is the case, you probably don’t want to downsize the images, and the Image> Image Size operation that Susan suggested may not be what you want to do.
Also, you didn’t say what the Image Mode of the images is. Since these were originally TIFF files, they could conceivably be 16-bit mode images, which would add an additional complication.
If it is your wish to preserve maximum detail for possible future large prints, then your primary need is higher file compression rather than downsizing. I use Genuine Fractals for that because it compresses considerably more than Photoshop’s PSD format with no significant loss of image detail. However, Genuine Fractals cannot do 16-bit mode images yet, so if your images are 16-bit, you might want to change their Image Mode to 8-bit.
Another alternative to JPEG is JPEG-2000, which uses wavelet technology rather than discrete cosine transforms. The wavelets allow you to have both higher compression and higher image quality at the same time. Compression ratios as high as 100-to-1 with decent image quality are possible with wavelets, while JPEGs at that compression ratio would give you garbage.
— Burton —
Quentin,
Burton makes a good point. It really depends on your intended usage for the images. Enlighten us, so we can give you more specific advice.
Bert
"web image" and "screen image" same thing. PPI doesn’t matter.
800×600 pixel image displays exactly same size whether saved at 72 or 7200 ppi.
Mac
Good commentary folks.
Susan (or anyone). I’m not sure I follow your description on the Image / Image Size…. when you say to <"uncheck" the Resample box, put in the smaller size dimensions, re-check the Resample box, and now change the resolution to 300.> If I just leave the Resample box checked and put in the new size and type in 300 on the resolution line it seems to give me the same thing. I don’t see the reason for the step of unchecking unless I’m missing something. Can someone elaborate? Thanks.
Gordon
Hi Bob,
I want to be able to print some of them, but there isn’t enough difference in image quality between a 6 meg file and a 125 meg file to make it worthwhile to keep the huge files. My printer is a HP 960C which prints at 600 X 600.
Someone else asked whether I just wanted wallet sized pictures — no, I want 5X7 and 8X10, but I want smaller file sizes.
Quentin
Susan,
Thank you very much. I’m afraid I created some confusion. The problem arose because the pictures were scanned at a very high resolution (1200 or greater). That’s what made the files sizes so large. I understand what you said about printer resolutions and how the pix should have been scanned.
Quentin
Wow!
Thank you, Burton. What a fount of knowledge there is on this forum.
I do want to preserve the opportunity of making big prints.
Quentin
Burton,
Where do you get Jpeg-2000 compression? I do not see an option like that in "save as" or "save for web". Or is this something new in CS?
Quentin,
If you intend to send your images with a commercial print job, I’d suggest a flattened 8-bit tiff with LZW (lossless) compression. Jpeg is fine for inkjet prints but the quality will erode everytime you open and resave a jpeg. You could always "save as" image-lowres.tif or .jpg with a resampled smaller image size so that you retain the original full resolution.
jpg2000 is available on the PS CS disk (but doesn’t automatically get installed) and also came with ACR1 if that was bought in the past.
Bert, Don, Rafael, Mac, etc.
I wasn’t very clear in my pixels-to-output resolution description. As someone mentioned, your browser doesn’t care if your image is 300 ppi or 72 ppi. What does matter is the total pixels. If you want the image to be roughly two inches across as viewed in the browser, you only need about 150 pixels total width. If you wanted to print the same image, one that’s 150 pixels across, you could print it 1/2 inch wide (300 ppi) and it would look OK. If you printed it 2 inches wide (75ppi), it would NOT look OK.
I was only using the required resolution standards as a means to achieving the end–the correct number of total pixels required for acceptable output, depending on output destination.
If your image was scanned at 1200ppi, at original size of 8×10, and you want to print 8×10, you still have more pixels than you need, by a factor of 4.
Gordon,
The steps I described accomplish a dual purpose of changing output size and selecting appropriate resolution. If either one or the other of these specifications is already correct, then you can do it the way you described.
If you want the image to be roughly two inches across as viewed in the browser, you only need about 150 pixels total width.
That part is dicey also, though.
Using combinations of 15" to 21" monitors, running at resolutions of 640×480 to 1600×1200, that 150 pixels might actual be 3" to less than 1" actual screen size.
That’s why there’s really no way possible to show an image at even halfway precise "actual known size" on someone’s monitor, unless you know exactly the screen size and resolution that monitor is set for.
Mac
That part is dicey also, though.
Very true, I was only offering a rough estimate, based on more common home monitor sizes, as opposed to the big honkin’ monitors we professionals have at work! We all have to make command decisions about size and placement when we design, and those decisions have to be based on something…
It is a common misconception, shared (surprisingly) by many otherwise knowledgable folks, that resolution should be set to 72 ppi for monitor viewing. As Wayne Fulton points out in his book, "Some Scanning Tips" the only reason to do this is to get a very general idea of its size on the monitor, but as Mac says, it won’t work for all monitors.
It’s really easier to just think of image size in pixels anyway IMO. Bert
True, Bert, but Susan does make a point, in that one must have at least some *general* idea of what physical size x number of pixels is going to appear to the viewer as.
As she says, 150 pixels wide will at least be in the rough ballpark of 2 inches wide on most 17-19" monitors, unless they are running very high or very low screen rez.
Mac
True…see my follow to Bert’s last comment…
Mac
Thanks for the info Susan.
Gordon
I wasn’t suggesting that Susan did not understand the resolution issue. As she explained in her later posts, she clearly does. I was just commenting generally that the "magic 72" is a common misconception. I see posts in these forums all the time that advise people to set the resolution to that for any Web images, etc.
It’s one of my "hot buttons" I guess. I have this reflex action…whenever I see that statement, I correct it. Can’t help myself…it happens automatically. 🙂
Bert
Bert,
You’re right, often people think that setting the resolution, to 72 or 300 or whatever, is an end of itself, when really, it’s just a means for determining the appropriate number of pixels for output size. Setting a 4000 pixel image to 72ppi won’t make it suitable for the web; you’ve got to get fewer pixels. And setting the 150 pixel image to 300ppi won’t make it less suitable for the web, or more suitable for printing to paper.
It took me 4 hours on the phone with my mother to explain this, when she was getting ready to buy a new scanner:
[Output Size] x [Output Factor] = Required pixels
[Required Pixels] divided by [Original size] = Resolution at which the original should be scanned
As we mentioned before, output size is a bit nebulous when you’re talking about web viewing. Multi-purpose Output Factors are 300 for print, and 75 for web. You could go as low as 150 for some home-grown print jobs and still get acceptable results. Your mileage may vary.
Susan,
I know about trying to explain this to people. It never fails to amaze me that some really smart people just can’t get the whole concept of pixels, resolution, printing and the Web. It’s almost like a mental block. Strange…
Bert
It never fails to amaze me that some really smart people just can’t get the whole concept of pixels, resolution, printing and the Web
Especially when they see that changing resolution changes image dimensions (pixels) in the Image|Size… dialog with resampling checked. It’s confusing for many.
Susan,
You spent four hours trying to explain this to your mother??? Good for her if she got it. Most mothers (and fathers, uncles and aunts etc.,) have a hard time opening e-mail. If your mother understands this she’s WAY ahead of the curve.:)
Gordon
My mom is the computer geek of her generation in my family. She doesn’t really do hardware work, but she does know how the different hardware components affect the computer’s functionality. She was doing html before me. She never learned any web languages beyond html, but she does alright. She was needing the new scanner because she hadn’t been able to convince my dad the photographer to get a digital camera, so they had several hundred negatives from their Alaskan road trip to scan. She couldn’t figure out what max scan resolution she needed to buy.
My mom is the computer geek of her generation in my family
Susan,
You must be VERY young! 🙂
Bert
Bert, Thanks, but no! I’m 39 (really!)–my mom is 64.
My folks are retired, and road-trip every year to wherever the road takes them, for 6-9 months. A few years ago they went all the way to St. John’s, Newfoundland, and last year they made it all the way to Barrow, Alaska. Wish I could go!
EDIT: Check last year’s Travelogue at <
http://www.millonig.net/>.
Susan,
LOL! Thanks but YES! 39 is young by my standards. I’m older than your parents…67. Suzanne and I went to Newfoundland a couple years ago. In fact, the most popular album on my website is the Newfoundland one. Check it out.
<
http://community.webshots.com/user/bigelowrs>
Bert
