At 11:29 PM 10/13/2002 -0700, you wrote: >What is the best way to get the 72 dpi images captured by a typical digi >cam to a more usable 150 or 300 dpi file without losing data or having >the program fill in the blanks? Short Answer: In Photoshop, do an Image -> Image Resize and UNCHECK "Resample Image". and change the DPI to whatever you want. Long Answer: Here is a message I posted to the National Press Photographer's Associaton on the subject. The person asking a question felt there was a resolution difference between JPEGs and TIFFs coming from the Nikon D1's. Its written to that, but it works for any image, scanned or from a digital camera. I really need to turn this into a web page. Now lets look at whats going on inside the camera with the "DPI" issue. There is no standard DPI for anything. 300, while common for magazines and color photo printers isn't whats common for news papers, and even then there is quite a variety. We use 170 dpi. For this tutorial, load in both a D1H TIFF and a D1H Fine JPEG. In Photoshop the Image->Image Size dialog box has two parts. The top half of the dialog box contains the physical dimensions of the file, or as it says "Pixel Dimensions". This is where you should see 2000 x 1312. The bottom half of the dialog is the "Document Size". This is the printed size. For the moment make sure "Resample Image" is unchecked. When you uncheck the box, you loose the ability to edit the Pixel width and height. Now change the width, height, or DPI at your leisure. Lets start with putting 200 dpi into the Resolution. Remember this is the print resolution, not the image resolution. When you put in the 200 dpi, the pixels at the top remain the same, 2000 x 1312. However the width of the printed image changed to 10 x 6.56 inches. Thats because 2000 pixels / 200 pixels per inch = 10 inches. The number if pixels did not change, just how big we chose to make it. Set the DPI to 300 and you get a 6.667 x 4.373 inch image. Again, the image didn't change in any way, just how many pixels we are going to use for each inch at print time. And as you noted, changing to 72 dpi gives you a 27" x 18" picture. Now for fun, change the Width to 8". See how it automagically changed the height to 5.248" (thats the "Contrain Proportions at work, it should pretty much always remain checked) and the DPI adjusted to 250 dpi. Thats because if you want to print 2000 pixels wide at 8", it will need 250 pixels per inch to make that print. Now switch back and forth between the TIFF and the JPEG. No matter what you set the Resolution to, the image stays at 2000 x 1312 pixels. All we have changed is print size. I have an action programmed that when I bring in an image for the news paper, I have it automatically change the document size to 170 dpi and I'm done with it. When I programmed that action, I made sure I had "Resample Image" unchecked because if I did have it checked evil things would happen as we will see next. Now, go back to one of your images and set the Resolution to 72 dpi and let it adjust the print width and height to the 27x18" size. Click on Resample Image. Now notice we can now edit our Pixel Dimensions. We won't at the moment. With Resample Image checked, if you change the pixel width or height, software will add or throw away data from the original to make the image file represent the new size. Lets say you wanted a 200x300 pixel image for a web page, you would check Resample image and make your height 200 pixels and the software would adjust the width to 305 (the D1H is a 6.1 x 4 aspect ratio). Go ahead and try that and see how it affected not only the actual image size, it adjusted the print size as well based on your DPI setting. Now lets be nice and put it back to 1312 pixels high and your width should jump back to 2000 (for that fact, you can set the width to 2000 and it will adjust the height to 1312 for you. Since we haven't clicked <OK> yet, no changes have really happened to our file. Now lets see where resample is evil. You just brought that Fine JPEG from your D1H into photo shop and you do an Image->Image Size. Your resample box is checked and you quickly go and change the width to something managable like 10". Photoshop obeys your wish and since Resample is checked, it changes the image's pixel dimensions along with the print dimensions to 720x472 pixels. You have a 10 x 6.56 inch image but at 72 dpi. But in a hurry you clicked the <OK> button and when it gets into Quark things start going nuts. Of course by this time you have saved over your original with the new smaller version. Now you try to fix things by going back in and changing the DPI and you get a better but not quite as good an image back. So to summarize the tool: With Resample checked, Image->Image Size changes the physical amount of data in the file. With Resample unchecked, it just changes the print characteristics. Now why Nikon picked 300 dpi for TIFFs and 72 for JPEGs is beyond my mind, If they would have picked something insane like 1 or 2000, it would have raised a flag that it needs changed before you print. Ideally, the next ones will be programmed to let you set that. So coming out of this, your image size is always 2000 x 1312. The setting in camera of 72 or 300 dpi is really meaningless. Its just a starting point that Nikon chose. You have to make that print size more meaningful using the Image->Image Size tool in Photoshop, being very careful with the Resample option. It generally should be off unless you know you want to upsample or downsample the image. Thanks, Rob -- Rob Miracle Photographic Miracles 203 Carpenter Brook Dr. Cary, NC 27519 http://www.photo-miracles.com
