resample

PK
Posted By
Petr Kohutek
Feb 18, 2005
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306
Replies
3
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Closed
Hallo

can anybody point me to a function in PhotoShop that will enable me to change the DPI of an image without changing any of the pixels?

I have some screenshots that I need to resample from 96 DPI to 200 DPI without affecting the pixels.
In Corel PhotoPaint I have used command Resample and checked the checkbox "Maintain original size" – then the dimension in inches or millimeters was automatically changing when I changed the DPI (and vice versa). In Photoshop I am not able to change the resolution without changing the dimensions, which always results in resampling (= changing the image a bit). The only way I have figured out was to remember the size in pixels, change the DPI and then write the original size in pixels back. This is quite inconvenient especially if I want to utilize this step in a one click automated process for converting of this kind of images.

Thanks in advance

Petr

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A
arrooke
Feb 18, 2005
Hallo

can anybody point me to a function in PhotoShop that will enable me to change the DPI of an image without changing any of the pixels?
I have some screenshots that I need to resample from 96 DPI to 200 DPI without affecting the pixels.
In Corel PhotoPaint I have used command Resample and checked the checkbox "Maintain original size" – then the dimension in inches or millimeters was automatically changing when I changed the DPI (and vice versa). In Photoshop I am not able to change the resolution without changing the dimensions, which always results in resampling (= changing the image a
bit).
The only way I have figured out was to remember the size in pixels,
change
the DPI and then write the original size in pixels back. This is quite inconvenient especially if I want to utilize this step in a one click automated process for converting of this kind of images.
Thanks in advance

Petr
You have to think about where these extra pixels are going to come from. Your image is currently 96 ppi. That’s all you have. The extra 104 doesn’t just materialize. You can add pixels, but this is a process called interpolating. The computer (Photoshop) averages as best it can from surrounding pixels and adds that to the image. In your instance you are wanting to double the number of pixels you have. Not good. You will be adding colour that really isn’t there to begin with. Obviously this will cause your image to suffer a loss in quality. Half your image will be made up of ‘faked’ colour.
If you want to proceed – I presume you want to reduce jaggies for printing purposes – use:
Image > Image size.
Tick all 3 boxes at the bottom of the dialog box and change the resolution to your hearts desire. This will not change the printed size (dpi and ppi are not one and the same), but will alter the viewing size on the screen. Why? Because you’ve added more pixels per inch – it takes up more screen area.
Keith.

PS/ Often, if you are only printing to a shitty home inkjet, you can increase pixels somewhat without noticing a huge difference. The type of paper used makes a difference too. Good luck.
MJ
Monty Jake Monty
Feb 18, 2005
If you turn Resample off you can change the Resolution but this changes the Print Size. Not the On-screen Size. Your image has "X" amount of pixels. At 100% viewing the computer will display these the same regardless of how you spread them out for print. Now, if you want an image to print out the same size with different Resolutions, i.e. more or less dots per inch, you are going to either add or subtract pixels. There is no getting around it.

Ex.: Image on-screen is 300px x 300px. Printing at 300dpi gives you a 1 inch by 1 inch print. Printing this image at 100dpi will either give you a print 3 inches by 3 inches or, you are going to have to get rid of 80,000 pixels to print a 1 inch by 1 inch pic. Making an image higher resolution at the same print size involves adding pixels at the same rate as subtracting them in the above example. Which is not recommended. There are programs and plugins that perform this task, creating pixels by averaging those in the near vicinity, with varying results. None great.

If all you want to do is change the Resolution without concern as to the print size, then go to Image>Image Size, uncheck Resample near the bottom of the dialog box and enter your new resolution in the Document Size area. You will notice in the dialog box that the print size has changed but not the total number of pixels. Hit OK. This will return you to the main screen. Open the Navigation palette to make sure you are viewing at 100%. Again, this procedure will not change your on-screen size (no change in number of pixels) but will change the print size.

Steve

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From: "Petr Kohutek"
Organization: Nextra CZ
Newsgroups: alt.graphics.photoshop
Date: Fri, 18 Feb 2005 10:57:59 +0100
Subject: resample

Hallo

can anybody point me to a function in PhotoShop that will enable me to change the DPI of an image without changing any of the pixels?
I have some screenshots that I need to resample from 96 DPI to 200 DPI without affecting the pixels.
In Corel PhotoPaint I have used command Resample and checked the checkbox "Maintain original size" – then the dimension in inches or millimeters was automatically changing when I changed the DPI (and vice versa). In Photoshop I am not able to change the resolution without changing the dimensions, which always results in resampling (= changing the image a bit). The only way I have figured out was to remember the size in pixels, change the DPI and then write the original size in pixels back. This is quite inconvenient especially if I want to utilize this step in a one click automated process for converting of this kind of images.
Thanks in advance

Petr

PK
Petr Kohutek
Feb 18, 2005
Wonderful unchecking the checkbox helped!
Now, when I know, it is so obvious.
Being used to see the "maintain original size" made me blind to it.

For Info: I am using the screenshots in technical documentation – and by setting the 200 DPI makes the images exactly the size to fit without having to resize them in the text editor. I know that it will be resampled at printing (the printer having another DPI) – the idea is not to add another transformation in the chain.

Thanks for both responses.

Petr

"Monty Jake Monty" wrote in message
If you turn Resample off you can change the Resolution but this changes the
Print Size. Not the On-screen Size. Your image has "X" amount of pixels. At 100% viewing the computer will display these the same regardless of how you spread them out for print. Now, if you want an image to print out the same size with different Resolutions, i.e. more or less dots per inch, you are going to either add or subtract pixels. There is no getting around it.

Ex.: Image on-screen is 300px x 300px. Printing at 300dpi gives you a 1 inch by 1 inch print. Printing this image at 100dpi will either give you a
print 3 inches by 3 inches or, you are going to have to get rid of 80,000 pixels to print a 1 inch by 1 inch pic. Making an image higher resolution at the same print size involves adding pixels at the same rate as subtracting them in the above example. Which is not recommended. There are
programs and plugins that perform this task, creating pixels by averaging those in the near vicinity, with varying results. None great.
If all you want to do is change the Resolution without concern as to the print size, then go to Image>Image Size, uncheck Resample near the bottom of
the dialog box and enter your new resolution in the Document Size area. You
will notice in the dialog box that the print size has changed but not the total number of pixels. Hit OK. This will return you to the main screen. Open the Navigation palette to make sure you are viewing at 100%. Again, this procedure will not change your on-screen size (no change in number of pixels) but will change the print size.

Steve

— faith \’fath\ n : firm belief in something for which there is no proof.
Webster’s Dictionary

From: "Petr Kohutek"
Organization: Nextra CZ
Newsgroups: alt.graphics.photoshop
Date: Fri, 18 Feb 2005 10:57:59 +0100
Subject: resample

Hallo

can anybody point me to a function in PhotoShop that will enable me to change the DPI of an image without changing any of the pixels?
I have some screenshots that I need to resample from 96 DPI to 200 DPI without affecting the pixels.
In Corel PhotoPaint I have used command Resample and checked the checkbox "Maintain original size" – then the dimension in inches or millimeters was
automatically changing when I changed the DPI (and vice versa). In Photoshop I am not able to change the resolution without changing the dimensions, which always results in resampling (= changing the image a bit).
The only way I have figured out was to remember the size in pixels, change
the DPI and then write the original size in pixels back. This is quite inconvenient especially if I want to utilize this step in a one click automated process for converting of this kind of images.
Thanks in advance

Petr

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