Image>Image Size
The Resolution is under Document Size
Larry Berman
Fabienne,
There’s probably nothing wrong with the images. DPI or PPI only matters when printing them: this value tells the printer how close adjecent pixels should be printed.
Also when scanning them it matters: 200 pixels per inch means that the scanner (if possible) divides each inch in 200 parts.
What really matters is the amount of pixels the image has. the larger, the better. You wrote you "took" images… How? did you scan them?
When printing: if the image is quite large, but "only" 72 ppi, then you schould make sure that "fit to page" or somthing similar is active in the printer software.
Correcting the images: in image size change whatever parameter that you want, but make sure resample is off. This way the image is unchanged, only the "printer instruction" is altered.
Rob
Fabienne,
The photos off your digital camera does not have PPI information in them. Photoshop defaults to 72 ppi (or 96ppi if set in prefs) when it finds no resolution info in the images. This is because most monitors have a resolution in that neighbourhood.
The quality difference you are talking about could be either compression (leading to a degraded image) or a smaller image (which means it is smaller in the XY dimensions – this has nothing to do with PPI).
For printing in high quality on an inkjet, you always want to set the PPI to ~240-300 PPI (with resample off).
Mathias
That makes it much clearer. What I get from your response is that the monitor will regardless display the image at 72 (or 96) dpi because that is the limit of its capabilities. PPI is a unit of measure in regard to the printer (which has higher capabilities than a monitor).
The size of the image is measured in vertical and horizontal pixels. Making the image fit into a smaller size gives a denser concentration of pixels and a finer look.
Rob, I "took" the images with my digital camera (a brand new Sony Cybershot at high quality level). That was why I was so shocked to see them listed at 72 dpi. But that was before I knew about dpi vs. number of pixels vertical/horizontal. Thanks for reminding me about the resample box.
So thanks to you all. If I have repeated anything to you in my words and I didn’t get it quite right, please feel free to correct that. But I think you were pretty clear.
I just ran an experiment. I had an image that was 2592 wide x 1728 wide. I took off the resample checkmark and reduced the size of it from 36" x 24" to 8" by about 6". Voila, the size changed the resolution jumped from 72 dpi to 259.2 dpi. So…great.
This means that if I want to take an image of a painting to make a poster at 16 x 20", and I reduce it to that size from 24 x 36 I can keep a good resolution for the printer. It sounds like it all hinges on having a big enough image with enough pixels so that if you reduce it, it will have a good enough resolution to be printed well.
There is one more question that strikes me now. Let’s say that I put my camera on highest quality. I take a picture and it is downloaded at 24 x 36" (which my camera is set up to do). I bring up the image in Photoshop and it reads out at 72 dpi. I need 300 dpi to make the poster well but the size I have to reduce it to is 11 x 14. I resize the image in Photoshop but the resolution is now 185 dpi. How can I bump up the resolution to 300 dpi without degrading the quality, will interpolation be good enough?
Thank you once again for your help. I really appreciate it.
Resampling at a higher resolution will reduce quality, but it might not do so visually. I regularly resize my digital camera files to 16×20 at 300 pixels per inch and make Lambda prints to sell at art shows. That’s 4800×6000 pixels. I even have a body of work created with a 2 megapixel camera (1200×1600 pixels) that I make large prints from.
Don’t let the rules or numbers stop you from experimenting. There are programs like Genuine Fractals that can improve enlargements on some types of files, as can Photoshop CS’s Bicubic Smoother.
Getting back to the original camera file. You can minimize the effects of a degraded image by using good photography basics to begin with. Whenever possible, always use a tripod and bracket for perfect exposure. Having a perfect file to work from will increase your chances of getting a good looking enlargement.
Larry Berman
Photoshop defaults to 72 ppi (or 96ppi if set in prefs)
Is this a new feature in prefs of CS?
Mac
Photoshop 7 and CS read the EXIF data as to the pixels per inch upon opening a digital camera file. What probably is happening is that the manufacturer of his camera programmed 72 pixels per inch into the EXIF.
But the pixels per inch doesn’t mean anything as it’s only the number of pixels that matter. There is no pixels per inch until the file is opened and saved as such. Just make sure to save your original out of camera files for archiving.
Larry Berman
Larry,
I´m pretty sure that it is Photoshop that defaults to 72ppi, not the cameras. Some cameras embed PPI info in their TIFF files though (usually 300ppi).
Mac,
Now you made me look! Its under Units and Rulers, screen resolution. A quick test would be to change this info to something obscure, and then open a camera file to check ppi.
Mathias
Its under Units and Rulers, screen resolution.
Had a feeling that’s what you meant.
That is the default for NEW documents. Has no affect at all on opening existing images.
Mac
Mac,
That is the default for NEW documents. Has no affect at all on opening existing images.
Then what happens if you open an image with no PPI information? Have you ever tried to open a GIF file in Photoshop? (Ofcourse you have – and at what ppi does it open?)
Maybe you and Larry are right that it is the camera makers that specify 72ppi as an EXIF default (I chekced, and all my files, coolpix 995 and Canon 10d, has 300ppi embedded in their EXIF). I just wonder WHY the heck they would do such a thing, if.
Photoshop has the old 72ppi default from way-back.
Maybe we should have an engineer ‘splain it.
Mat
That would be great.
I can’t grasp the line of reasoning that Photoshop uses for listing all files as having 72dpi. Ok, I could justify it as a default for a monitor, but why have it there at all if it is always the same, that is until you want to change it? Don’t see the reasoning (except in a convoluted way).
Still seems like such a simple thing, something you wouldn’t question unless you had a special need.
-Fabienne
Photoshop, like most imaging programs, opens an untagged image at 72. A few have ppi options for existing non-tagged images, like PaintShopPro. Of course, if image is tagged as 72, PS will also open it at that, but for a different reason.
Version 7 was the first version to honor EXIF ppi tag also (in addition to header tag in TIFF/PSD/etc).
Mac
Again I am baffled. I opened some images in the file browser that I took with my spiffy new digital camera. They (as usual) were shown at 72 dpi. Then I opened an image on Ben Willmore’s CD (which came with his book on Photoshop)and was surprised to see it listed as 300 DPI. How come he has the resolution listed high and I only have mine listed at the low level?
This is sort of flying in the face of everything I learned from the previous part of this discussion.
Fabienne,
#1: It is PPI not DPI.
#2: IT DOESN’T MATTER!!!
Set your output size when you print. That is the ONLY time you need to worry about it. The quality isn’t going to be any better on the screen while you are working no matter what the resolution is set to.
You could set it to 1 PPI or 6000 PPI and it isn’t going to make a bit of difference.
If you are really that picky change the settings in your camera. Most digital cameras allow you to set the EXIF resolution to whatever you want it to be.
Ignore the 72 dpi!!!!!!!
Question: How large is your file? THAT is the criteria.
First – change the resolution to what your printer likes (I use 280 for my Epson 1280 and wide format Epson 7600). Go to Image, Image Size. Make sure Resample is unchecked.
Second – notice that your document size has now gotten a LOT smaller (mine typically go from 59" wide to 14" wide. Don’t worry.
Third – to make larger prints check resample and pick a size relative to the paper you are using. This is called resampling to a larger print size. My data at 10" x 14" typically prints up to 20" wide with no problem – or even larger if viewing distance will be increased.
Fabienne,
I know it’s confusing. Listen to the folks above – all veterans of this forum. Since PPI really only matters (in a manner of speaking) when you print, only concern yourself with it when you DO print. In that case, you can resize the image, without a destructive resample so that it prints with the appropriate resolution to your printer, as Steve suggested.
If it’s for screen work, it simply doesn’t matter. That is why photoshop is tagging it as a default 72 ppi – because it doesn’t really matter for screen work. In a sense, it’s like asking "how high is water?" We don’t measure water in height, although in some circumstances, it can be useful to do so.
If you really want to get your arms around "resolution", then visit Wayne Fulton’s Site on Scan Tips <www.scantips.com>.
If you want to make it read "correctly" in photoshop without resizing, then as Photo Help said, work on your camera settings so that it embeds the resolution in the image (EXIF info). Then Photoshop will read it. But if you do that, you will not see any difference in your image <whispering> because it doesn’t matter.
Rest assured you aren’t the first to have these questions, however, some time at waynes site should help.
Peace,
Tony
Thank you, Tony. I suppose that the idea of ppi (dpi) had gotten so entrenched in my vocabulary that thinking about these things in another way gets daunting. I wlll visit the Wayne Fulton Site and read it very thoroughly. His address has changed, it is <
http://www.scantips.com/> now. It looks like a very good place to research. Thanks again.
Tony’s got a way of explaining things… good on Tony! 🙂
