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Old Jan 13, 2006, 2:25 PM   #1
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I have heard people in this forum saying in certain topics to make sure the resample box is ticked, and then in others untick the resample box, could someone explain what the resample box does?
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Old Jan 14, 2006, 5:44 PM   #2
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Resampling refers to changing the pixel dimensions (and therefore, display size) of an image. When you downsample (or decrease the number of pixels), information is deleted from the image. When you resample up (or increase the number of pixels), new pixels are added based on color values of existing pixels. You can specify an interpolation method to determine how pixels are added or deleted.

The resample box just turns this process on or off when you want to resize an image.

As to what this does and when to use or not use it, let's take some examples:

Say you have an image that is listed at a resolution of 72ppi (pixels per square inch) and a document size (the physical dimensions to which the image would print at the given resolution) of 20x30 inches.
Now, 72ppi is good enough resolution for web applications, but if you want to get a really good quality print, 72ppi is not enough resolution. For an inkjet printer, you want somewhere around the 240-300ppi range for maximum quality.

Let's say that you then changed the document size of the image in the image size dialog (Photoshop) to 10x15 inches. If you check (turn on) the resample box, what you have would be an image that would print at 10x15 inches but still have a resolution of 72ppi because the program would downsample (delete image information) the image to maintain the same resolution that you started with before you changed the document size. If you uncheck (turn off) the resample box, you would end up with an image that would print out at 10x15 inches at 142ppi. That's because with resampling turned off, the total number of image pixels is not changed, and when you cut the document size in half, all the pixels are squeezed into an area half the size that they occupied before, causing the image resolution to double.

Okay, 142ppi is better for printing than 72 is, but we wanted to go for 240-300ppi for the best results. Repeating the above procedure of halving the document size again with resampling turned off, we get a print of 5x7.5 inches with a resolution of 284. That should be good enough resolution to get the best print you can out of your printer.

What if you want to print an 8x10 at 284ppi resolution? Well, you don't have enough pixels in the image to do it. We've already established that there are only enough pixels to give a 5x7.5 at that resolution. This is where resampling must be used. In this case, you enter the document size (8x10) that you want in the appropriate fields and enter 284 in the resolution field. Now you must check (turn on) the resample box so that the program will create enough additional pixels through a mathematical process called interpolation to give you the specified resolution.

In another example, if you want to post that picture on the web without someone having to scroll all over the place to see the whole thing, the original full size of 20x30 at 72ppi is way too big. The 72ppi resolution, in this case, is good enough. what you want is to reduce the physical borders of the image to a size that will fit onscreen so that someone can see it all at once. You could keep the 8x10 boundaries if you wanted to. (Really, in web applications, you go by pixel dimensions rather than the printing dimensions, but Photoshop usually changes both the pixel dimensions and the document size in the same proportion no matter which one you change manually.)

So, you choose your 8x10 borders, keep the 72ppi resolution and check the resample box. Now what happens is that the program has to downsample -- it has to use a mathematical algorithm to throw out enough pixels to give you the number of pixels specified by your choice of image size/resolution.

Of the two directions in resampling, upsampling (interpolation) is usually more problematic as far as image quality is concerned because the program has to literally "invent" pixels that are not in the original image. It just guesses what "should" be there if the original image was recorded at a higher resolution.
Downsampling just deletes pixels in a manner designed to reduce the image size in an even manner; the end result is still made up of only original information.

I'm sure there's more to be said, here, but I didn't mean to write a novel. If something remains unclear, just ask.

Grant


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Old Jan 15, 2006, 1:55 PM   #3
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Thank you so much for giving up your time to explain what you have made much much clearer an issue for me. What you have explained, to be honest i have not found anywhere, an article on resampling explained so clearly. Once again many thanks. regards. Bev.
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Old Jan 17, 2006, 2:12 PM   #4
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The steps I use to take a 3264 x 2448 image and print it at 4" x 6" is way too complex. Would you let me know the work flow you use? Has to be simpler than what I do!

I use Photo Shop Elements 2 for post processing and a Cannon iP5000.

Thank you

Stan

granthagen wrote:
Quote:
Resampling refers to changing the pixel dimensions (and therefore, display size) of an image. When you downsample (or decrease the number of pixels), information is deleted from the image. When you resample up (or increase the number of pixels), new pixels are added based on color values of existing pixels. You can specify an interpolation method to determine how pixels are added or deleted.

The resample box just turns this process on or off when you want to resize an image.

As to what this does and when to use or not use it, let's take some examples:

Say you have an image that is listed at a resolution of 72ppi (pixels per square inch) and a document size (the physical dimensions to which the image would print at the given resolution) of 20x30 inches.
Now, 72ppi is good enough resolution for web applications, but if you want to get a really good quality print, 72ppi is not enough resolution. For an inkjet printer, you want somewhere around the 240-300ppi range for maximum quality.

Let's say that you then changed the document size of the image in the image size dialog (Photoshop) to 10x15 inches. If you check (turn on) the resample box, what you have would be an image that would print at 10x15 inches but still have a resolution of 72ppi because the program would downsample (delete image information) the image to maintain the same resolution that you started with before you changed the document size. If you uncheck (turn off) the resample box, you would end up with an image that would print out at 10x15 inches at 142ppi. That's because with resampling turned off, the total number of image pixels is not changed, and when you cut the document size in half, all the pixels are squeezed into an area half the size that they occupied before, causing the image resolution to double.

Okay, 142ppi is better for printing than 72 is, but we wanted to go for 240-300ppi for the best results. Repeating the above procedure of halving the document size again with resampling turned off, we get a print of 5x7.5 inches with a resolution of 284. That should be good enough resolution to get the best print you can out of your printer.

What if you want to print an 8x10 at 284ppi resolution? Well, you don't have enough pixels in the image to do it. We've already established that there are only enough pixels to give a 5x7.5 at that resolution. This is where resampling must be used. In this case, you enter the document size (8x10) that you want in the appropriate fields and enter 284 in the resolution field. Now you must check (turn on) the resample box so that the program will create enough additional pixels through a mathematical process called interpolation to give you the specified resolution.

In another example, if you want to post that picture on the web without someone having to scroll all over the place to see the whole thing, the original full size of 20x30 at 72ppi is way too big. The 72ppi resolution, in this case, is good enough. what you want is to reduce the physical borders of the image to a size that will fit onscreen so that someone can see it all at once. You could keep the 8x10 boundaries if you wanted to. (Really, in web applications, you go by pixel dimensions rather than the printing dimensions, but Photoshop usually changes both the pixel dimensions and the document size in the same proportion no matter which one you change manually.)

So, you choose your 8x10 borders, keep the 72ppi resolution and check the resample box. Now what happens is that the program has to downsample -- it has to use a mathematical algorithm to throw out enough pixels to give you the number of pixels specified by your choice of image size/resolution.

Of the two directions in resampling, upsampling (interpolation) is usually more problematic as far as image quality is concerned because the program has to literally "invent" pixels that are not in the original image. It just guesses what "should" be there if the original image was recorded at a higher resolution.
Downsampling just deletes pixels in a manner designed to reduce the image size in an even manner; the end result is still made up of only original information.

I'm sure there's more to be said, here, but I didn't mean to write a novel. If something remains unclear, just ask.

Grant

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Old Jan 18, 2006, 8:08 PM   #5
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Resizing stuff to 4x6 is one of those things that sounds, on the face of it, about as complex as spreading the right amount of peanut butter on your pbj sandwich. But, once you get into it, it can be as frustrating as when the extra-chunky variety rips holes in your bread.

Stan, there are different strategies that can be used depending on whether you want to include all the image in the print or just some of it. You didn't specify, so I feel emboldened to provide a "free range" reply.

The bugger with doing 4x6's is that you're printing to a different aspect ratio (AR) than most digital cameras provide. It's like trying to stuff a square peg into a round hole: you have to either bend the corners of the peg or whittle them down.

If you want to include the whole image in your print, you have to "bend the corners" to shoe-horn a 4:3 AR picture into a 3:2 AR print. This is pretty pain-free. You just open the Image Size dialog box and make sure that the Constrain Proportions box is not checked, the Resample Image box is checked and enter 4 inches and 6 inches in the appropriate boxes under Document Size, choose the resolution you want and click Okay. The picture will be stretched a little bit, but you can usually get away with it on things like landscapes. With subjects that have more regular shapes that people are familiar with, you might find the distortion unacceptable. If that is the case, you have to go with the second option -- whittling down the corners of the peg (cropping).

About the easiest way to crop to a 4x6 that I've found is to click on the Rectangular Marquee Tool and choose Fixed Aspect Ratio from the Style box on the marquee's tool bar. Then put 3 and 2 respectively in the Width and Height boxes. This is cool because it constrains the selection box drawn by the marquee tool to a 3:2 AR and whether you choose to crop out a small portion of the image or get as much of it as you can, the selection box is always giving you the right AR so that once you make the final crop, it's easy to resize the crop either up or down in the image size box to a 4x6!

After you get the Marquee selection box the size that you want, you can click inside the box and drag it around to get the crop area you want. Then, go to Image > Crop to delete the part of the picture outside of the selection box.

After cropping, you just go to the Image Size box, make sure that the Constrain Proportions box is checked, then enter 4 inches and 6 inches in the appropriate Document Size field.Look at the value in the Resolution field after you input the document size. If the resolution is outside the value range that you want, then put a check in the Resample box and enter the resolution you want in the Resolution field.
Click Okay.

The picture should now be resized to print at 4x6 at the resolution you just specified.

Is that less hassle than the method you have been using? If not, post what you do, and I'll do it your way.

Something that could save you some trouble would be if you have one of the cameras that give you a menu option to shoot pictures at the 3:2 AR. That might save you the trouble of cropping if you liked the picture as it was shot.

I don't know how many features that PE2 has in common with Photoshop, but if you can create Actions it might end up saving you time if you had a lot of pix to resize. You should be able to record a "Stop" in the Action that would allow you to manually select the crop for each pic, then play the rest of the Action when you were done. If you can execute Actions in Batch mode, it would let you run through whole folders that way.

Grant
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Old Jan 18, 2006, 10:30 PM   #6
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Snkline, as you have a Canon printer, do you not use the Canon EasyPrint software for printing? I find it easy to use, and rarely need to do any resizing for 6 x4 or other print sizes prior to using this Canon EasyPrint.

Briefly in this program, after selecting the image, one selects the paper type & size, then in the layout click on" Trim". This displays a crop square on the image at the exact aspect ratio of the paper size you selected. The crop square can be altered & repositioned as you wish for the print. Multiple images per page can also be printed, bordered or borderless.

AFAIK, this does not alter, resize or resample the original image file at all, and retains the maximum image pixels for the best print PPI.

Maybe you already know of this. If not it's worth a try.
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Old Jan 18, 2006, 11:09 PM   #7
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The easiest way to get a 4 X 6 in Elements or Photoshop is to choose the crop tool and put 6 inches in the width and 4 inches in the height – or the other way round. Put NOTHING in the PPI box. It will constrain the crop to the right ratio and you will end up with 4 X 6 in your print size and keep all the pixels you don't crop out. The crop toolbar shows at the top of the screen when you choose the crop tool.

You can look in the size box to see what PPI you ended up with, but you will have plenty for a 4 X 6 unless you crop out a very small portion of the image. I see no reason to resample if you have plenty of pixels for a print. Resample slightly deteriorates an image because the software has to guess at colors for pixels that don't exactly line up with the original. Not that you would notice on a 4 X 6 print, but it is a good habit to not resample unless you have to.

I find that Canon Easy Photo Print alters the color balance even when I don't have it enhance the image in any way. If I print directly from Photoshop or Irfanview I get the same print and they reflect the color balance I have chosen. But if I print from the Canon software it is slightly different, often in ways I don't like.


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Old Jan 19, 2006, 8:08 AM   #8
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granthagen wrote:
Quote:
Resizing stuff to 4x6 is one of those things that sounds, on the face of it, about as complex as spreading the right amount of peanut butter on your pbj sandwich. But, once you get into it, it can be as frustrating as when the extra-chunky variety rips holes in your bread.

Stan, there are different strategies that can be used depending on whether you want to include all the image in the print or just some of it. You didn't specify, so I feel emboldened to provide a "free range" reply.
Quote:
Grant
Grant: Thanks for taking the time to answer my question. Now another one: How do you 'save as' or is there a way of 'saving' as is without over-writing the original image?

Thanks

Stan
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Old Jan 19, 2006, 8:13 AM   #9
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slipe wrote:
Quote:
The easiest way to get a 4 X 6 in Elements or Photoshop is to choose the crop tool and put 6 inches in the width and 4 inches in the height – or the other way round. Put NOTHING in the PPI box. It will constrain the crop to the right ratio and you will end up with 4 X 6 in your print size and keep all the pixels you don't crop out. The crop toolbar shows at the top of the screen when you choose the crop tool.

You can look in the size box to see what PPI you ended up with, but you will have plenty for a 4 X 6 unless you crop out a very small portion of the image. I see no reason to resample if you have plenty of pixels for a print. Resample slightly deteriorates an image because the software has to guess at colors for pixels that don't exactly line up with the original. Not that you would notice on a 4 X 6 print, but it is a good habit to not resample unless you have to.

I find that Canon Easy Photo Print alters the color balance even when I don't have it enhance the image in any way. If I print directly from Photoshop or Irfanview I get the same print and they reflect the color balance I have chosen. But if I print from the Canon software it is slightly different, often in ways I don't like.

I find Canon Easy Photo Print to change the colors to the red side. I may be doing something wrong in the use of CEPP!!.

Thanks for replying

Stan
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Old Jan 19, 2006, 8:20 AM   #10
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Baz wrote:
Quote:
Snkline, as you have a Canon printer, do you not use the Canon EasyPrint software for printing? I find it easy to use, and rarely need to do any resizing for 6 x4 or other print sizes prior to using this Canon EasyPrint.

Briefly in this program, after selecting the image, one selects the paper type & size, then in the layout click on" Trim". This displays a crop square on the image at the exact aspect ratio of the paper size you selected. The crop square can be altered & repositioned as you wish for the print. Multiple images per page can also be printed, bordered or borderless.

AFAIK, this does not alter, resize or resample the original image file at all, and retains the maximum image pixels for the best print PPI.

Maybe you already know of this. If not it's worth a try.
I find that Canon's Photo Print changes the color from that shown on the monitor. PS Elements prints very much closer to the monitor's image. I just received the iP5000 so I may have set something wrong in it's color settings.
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