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dpi or ppi


Welles said...When you first open the Image Size dialog, note what the pixel dimensions are. Now change the Resolution to 300dpi. See the pixel dimensions increase approximately 4 times. Change the pixel dimensions back to their original size and the resolution doesn't change. Now with the original pixel size and the 300dpi, the Document size is what will print in inches.

Welles

Maybe things have changed in CS, but I'm a little suprised by your approach to changing the dpi. Surely you just uncheck the Resample image check box. This will immediately show the size, in inches, of a print for any dpi you type in. This is certainly the simplest method in PS7.

Sark
 
You're right, Sark. I should have mentioned that. What I was trying to do was provide step by step simple directions which would point out the relationship of image size and resolution while allowing Melissa to print her images. Thanks for your addition, its most welcome.
 
I was under the impression that the 'resampling' was only if you were increasing the image beyond the original????

Thanks
 
Resampling occurs if you change the pixel size either up or down. If you are just changing resolution and have resampling unchecked, the pixel dimensions don't change. I'm glad Sark added that.
 
OH! So if I want to change 'just' the dpi, then I change the resolution and then uncheck the resampling box. That way I do not have to retype the information.
 
Alright you mentioned if I needed to upsize larger from the original that I would need to use a bicubic something.

Can you explain this further, also what is the 10% upsizing method? Do you up it 10% each time and then save and then open and upsize again 10% untill you get to the large document you need?

For example I have a canon 20D My photos come out about 3504X 2336 if I want to increase that so I can print a 16 X 20 what would your recomendations be as to steps?

THANKS!!! :)
Melissa
 
Hey Melissa! I got busy yesterday and never got back to the computer.? ;)

Many pros liked the 10% method which was also called the Stairstep method of upsizing. When Photoshop came out with new algorithms for resampling in PS CS, they had increased in quality enough that returning to a one step resizing became as good or better, so that making all those extra steps (or running an action) seemed just extra effort.

Mostly people suggest using Bicubic Smoother for upsizing and Bicubic Sharper for downsizing. Those options are available immediately to the right of the Resample Image: check box in a dropdown menu. I'd suggest experimenting with each of the different algorithms on copies of the same image. Then zoom in on a particular detail and see how each differs.
 
I'm probably repeating much that has already been said, but it may clarify some points.

All you really need to understand is that the DPI setting has no effect on a displayed image; it only effects the printed image. Think of it as a separate text file that is saved with the image and tells the printer how large the pixels should be printed. This info is only relevant to the printer.

The DPI setting your camera chooses is of no consequence; it is only the number of pixels that matter. The DPI you choose, prior to printing, determines the printed image size.

Even the recommended 72DPI setting for a web image is irrelevant because the web only concerns itself with the number of pixels in an image. You can upload the same image at 72DPI, or 300DPI and it will display identically with no difference in file size.

PhotoShop can confuse beginners because, with Resample image enabled, it lets you increase the number of pixels via the DPI setting. Increase the DPI and the pixels print smaller, but PhotoShop adds pixels (upsamples) to ensure the image prints at its original size in inches.

Basically, for display, you only need worry about the number of pixels. When printing, the size of the pixels (DPI) are important.

Sark

PS...In my experience, standard bicubic upsampling followed by sharpening with Unsharp mask, or similar, does as good a job as any seperate plug-in, and offers more control. I don't have CS, so cannot comment on its ability, but I suspect it is as good as any other method.
 
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