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Old Mar 9, 2006, 1:07 PM   #1
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Please help. I need to make a 28" by 65" poster using a digital image I shot on my Canon 20D. I shot in the RAW+JPG (highest quality) mode, but I don't know much about using RAW images and I know nothing about interpolation.

Any advice on whether it will be possible to print this large and if so, how? I would appreciate simple advice for the non-technically-savvy.



Thanks!!
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Old Mar 9, 2006, 1:19 PM   #2
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What editing and conversion software are you using?
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Old Mar 9, 2006, 1:23 PM   #3
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Just the Canon software that came with the camera and photoshop 7. I also have photoshop elements but haven't used it yet.
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Old Mar 9, 2006, 8:19 PM   #4
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You will be working with 54 PPI. You want to upsample that – I would suggest to 150 PPI. If you have plenty of RAM you might go to 200. All that does is smooth it a little. Better yet, call or email the place that will be printing it and ask for their suggestions. You might find they prefer to do any upsample themselves.

Your first step in Photoshop would be to select the crop tool and put 65 inches in the width and 28 in the height. Don't put anything in the resolution box. Crop the image to the right proportions.

I usually try Auto Levels first. If I don't like what it did I go back a step in the history and use another approach. It is quite sophisticated and works in the separate channels. My preferred approach for any color and saturation adjustments is selective color.

Try using unsharp mask with 16 in the amount and about 150 in the radius. It will make the image crisper. If you don't like it go back a step in the history. For regular sharpening I would use SharpControl if you don't have special sharpening software. It is free and does a great job. Save your image as a TIFF and open it in SharpControl. You can get it here: http://www.photo-freeware.net/category-downloads.php

My favorite upsample method is called stepped interpolation or SI. With that large an image I would upsample in 10% steps. You can make an action that will do 5 steps and repeat the action until the resolution is right. There is a % choice in the size box.

Genuine Fractals is good too, but you have to buy it. Some people like to use Bicubic Smoother, but I wouldn't do that for a poster. Luminous Landscape says the best Photoshop method is to upsample about 20% higher than you need with Bicubic Smoother and then downsample back to the size you want with Bicubic Sharper.

I would work with the raw right in Photoshop if you have a recent version with the conversions installed.

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Old Mar 10, 2006, 10:14 AM   #5
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thanks, slipe. Is my version of photoshop (7.0) able to work directly with Raw files? How do I do the stepped interpolation?
talia
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Old Mar 11, 2006, 3:00 PM   #6
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PS7 won't work directly on RAW files unless it has the Adobe Camera Raw plug-in -- which Adobe doesn't provide for that version anymore. You might be able to use your Canon Raw converter as a PS plug-in, but that still wouldn't allow PS to edit the RAW file.

To do the stepped interpolation, open the image in PS, go to Image>Image Size and make sure that both the Constrain Proportions and Resample Image boxes are checked.
Then click on the little arrow in the Pixel Dimensions dialog box and change the meassuring units from Pixels to Percent. Then just change the 100% figure to 110% and press Enter. Keep doing this until you get the measurments in the Document Size box to where you want them.

If you do this a lot, you can even make it into an Action and automate the whole process or assign the Action a "hot key" on your keyboard so that you can do each iteration by pressing one key.

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