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Old Dec 5, 2003, 5:37 AM   #1
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Default Resolution Confusion - an explanation for beginners...

Resolution?... what size? ...Why 72 dpi??

OK...
This resolution/sizing stuff is very confusing for newbies. In response to a question "bwilly" had, I thought I'd give it a shot. I've wanted to give my take (simplified hopefully!) on this for quite awhile now...

A lot of confusion comes from photo sizing, print resolution, and computer resolution. The first question usually is:
"Why do my pictures show up at 72 dpi when I save them to my computer from my camera?"

First, to keep it really simple, forget the "72 dpi" measurement even exists, as it just causes confusion, and is even wrong (the "inch" part when it comes to computer resolution)...

The best way to think of this unit of measurement is just the "ACTUAL PIXELS" of the photo when viewing on your monitor - e.g. when the photo goes to your computer from your camera, you are seeing each pixel at it's actual size. That's it! That's all this measurement means.

I'll use "bwilly's" cannon G5 as an example...
When you take a picture with your particular camera (at high rez) it captures an image that has a total of 2900 x 1800 pixels. Now look at what your computer monitor resolution is set at. Lets say it's set at the most common monitor setting - 1024 pixels wide x 768 pixels tall***. When you download the pic to your computer, and view "ACTUAL PIXELS" in your software's file menu, the pic will be larger than your monitor running way off the screen. In this case (at 2900 x 1800 pixels) almost 3 times the screen size of 1024x768...Get it?!

For sizing a photo size, you have to think in two completely different ways...Print, and Web/email.

Print:
Now let's say you want to make a 5X7 print (or in this case proportionately a 5x8 without cropping some off the top). In your software, again while viewing in the "actual pixels" mode, choose "image size", then make sure to have "resample image" UNCHECKED**. Resize the print to 5 "INCHES" tall. Then click OK. You know you've done it right if it is instantaneous. It will seem as nothing has happened, because nothing has. You haven't done anything to the photo. The picture hasn't changed in size at all. This is just information for the printer. It will now print your image at 5 inches tall. And all those millions of pixels that run way off your monitor, will be put into that small 5x8. So each pixel will be really, really, really SMALL - making for a very high-resolution print...Get it?!

Web/email:
Now let's say you want to email that same photo or put it on a web site. Again, computer monitors are measured in pixels - regardless of physical screen size. The most common measurement is 1024 pixels wide x 768 pixels tall. This is the resolution on just about all laptops, and most CTR monitors are set this way by default. Now if you email, or put that photo as it is on the web, it will run way off most screens. So in this case you really do want to change the size of the photo. You want to make it SMALLER (the actual pixel size) so it will fit nicely on a monitor. 400-500 pixels tall, by whatever width, is a pretty good size. This will fit nicely in the middle of just about any monitor (even those older ones that only have 640 x 480 pixels). Now under image size, make sure to CHECK "resample" image**. In the resize box you then size by PIXELS, not inches. Lets say you choose 500 pixels tall, which will make it about 800 wide. This will take your multi-million mega-pixel photo and completely redo it "RESAMPLE" it to make it about 400,000 pixels or so, and useless for print! Make sure to "SAVE AS" and not "SAVE", or you will turn your high rez original into a photo only good for web/email.


** IMPORTANT:
So many newbies have ruined photos because of the default setting in PhotoShop (not sure about other software) is set/checked to "RESAMPLE" image. IMO this is not intuitive and is not good. PhotoShop should change this. So many will not understand this and size their photos to 4x6, 5x7, and not UNCHECK "RESAMPLE" image. What happens is they inadvertently reduce the photo's "ACTUAL PIXEL" size and wonder why their prints look so "digital" - being able to see those few thousand "big" pixels on their prints, verses the millions of "small" pixels which you wouldn't be able too see. And the worst case is they "SAVE" and not "SAVE AS" a separate file, thus ruining their originals.

*** If you don't know how to check your monitor’s resolution go here (for PC users):
http://www.techlead.tusc.k12.al.us/f...sol/mresol.htm

I hope my 2-cents worth will help someone!
- Mike H
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Old Dec 5, 2003, 10:54 AM   #2
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That was a nice simple description Mike. I am sure it will help people understand the basics.
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Old Dec 5, 2003, 12:23 PM   #3
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Good theory but not too many beginners want to print 4 X 5 1/3 or 5 X 6 2/3 or 8 X 10 2/3 images. None of the current standard sizes are in the same ratio as most non-DSLR images, and even the DLSRs and a few others are only good for 4 X 6.

Say you want to print a 4 X 6 from a standard 3 X 4 ratio digital image. For Photoshop Elements or Photoshop open the image and select the crop tool. Put 4 and 6 in the appropriate width and height boxes. Put nothing in the resolution box. Drag the cursor across the image and notice it maintains the proportion of 2:3, and that to use as much of the image as possible you have to lose some of the top and/or bottom of the image. You can grab the corners or sides of the crop to pull the crop in or out or grab inside the crop and reposition it. When it is cropped the way you want go Image>Crop. You now have an image that will print 4 X 6 undistorted and that has retained all of the pixels you didn’t crop out.

For most 4 X 6 prints you would have to go no farther as far as sizing. You can just print the image directly from Photoshop or Elements. If you want to save the cropped image to a folder for printing later make sure to “Save as” so you don’t lose the original and save it as a TIFF so you don’t degrade the image with another compression.

If you are printing a larger image or cropped a lot out of the image it is a good idea to go Image>Image Size and see what PPI you ended up with. Everyone has a different threshold for how low a PPI they will print, but I usually upsample if the PPI ends up less than around 150PPI. If the PPI is too low check the “Resample” box and just put 300 pixels/inch in the resolution box. This won’t add detail but it sometimes smoothes out the print. Don’t resample as a standard practice as it slightly degrades the image. Do it only if the PPI is low enough that the print would look grainy.

If you don’t have an editor that lets you crop to a standard print size without a resample someone on another thread came up with some freeware that will do it.
http://ekot.dk/programmer/JPEGCrops/ and
http://www.studioline.net/EN/downloa...ic/default.htm

For any resizing you want to make sure “Constrain Proportions” (Photoshop/Elements), “Preserve aspect ratio” (Irfanview) or something similar is checked so that you don’t distort the image.
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Old Dec 5, 2003, 12:49 PM   #4
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Slipe,
I was just trying to explain resolution/sizing as SIMPLY as possible (and not cropping or upsampling...) so they understand what is happening.
- Mike
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Old Dec 5, 2003, 2:54 PM   #5
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Quote:
So many will not understand this and size their photos to 4x6, 5x7, and not UNCHECK "RESAMPLE" image.
You would have to uncheck Constrain Proportions to do that and end up with a distorted image. You don’t set 4 X 6 or 5 X 7 in the image size box unless the image is already in one of those proportions and they usually aren’t. For printing a fixed size from Photoshop or Elements there is no reason to open the image size box unless one wants to upsample – or check to see if one wants to upsample.

I have no idea what sort of digital image might produce a 5 X 8 without cropping BTW. With a 4:3 ratio setting 5 inches in the height gives 6 2/3 inches width and if one happens to have a 3:2 image 5 inches height gives 7.5 width. To print a 5 X 8 you would have to trim off the top and bottom with any standard digital image or uncheck Constrain Proportions and stretch the image.
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Old Dec 5, 2003, 10:53 PM   #6
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You are creating a debate where their is none. And this is not a "theory". A theory implies it may be true, but I have to prove it!!

I'm just trying to clearify monitor/print resolution with "facts" in a way a beginner can understand (I have a lot of beginner friends now!). If my facts are wrong I don't mind be corrected. If you read my post carefully, I'm not even talking about cropping which you brought up (I wanted to avoid that to create confusion). I'm just trying to give a simple explanation of RESOLUTION (not cropping) and I used bwilly's example (1800x2900 pixels) which proportionatly is 5x8 (8.056 to be exact).
- Mike
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