300 Down to 72 — with Same Onscreen Size

S
Posted By
sigerson
Sep 24, 2004
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457
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How do I reduce 300 dpi .jpgs or .gifs to 72 dpi in Photoshop while keeping them the same size on the screen?

For example, say the file is 1024 x 768 at 300 dpi (178 kb). Through "Image Size," I change the resolution to 72, but the picture shrinks to around
247 x 184. Well, I want it at the original screen size, just at a lower dpi. When I restore the pixel width to 1024, while keeping it at 72 dpi, the print dimensions balloon way out so that the file is as huge as when I started. "Save for web" doesn’t help. By the way, do you save website .jpgs as "High?"

I don’t expect to be printing these, but am working with copies of the original files just in case.

Thanks, all.


Steve Holmes
Executive Producer
"The New Ball Game"
"RailFAN"

Master Retouching Hair

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N
nomail
Sep 24, 2004
Steve Holmes wrote:

How do I reduce 300 dpi .jpgs or .gifs to 72 dpi in Photoshop while keeping them the same size on the screen?

For example, say the file is 1024 x 768 at 300 dpi (178 kb). Through "Image Size," I change the resolution to 72, but the picture shrinks to around 247 x 184.

Just deselect ‘Resample image’ in the image size box.

Well, I want it at the original screen size, just at a lower dpi. When I restore the pixel width to 1024, while keeping it at 72 dpi, the print dimensions balloon way out so that the file is as huge as when I started.

From what you say, I understand that you want a lower dpi value because you think that this will decrease the file size. It will not. The file size depends on the number of pixels, not on the resolution. If you want to keep the same number of pixels but at a smaller file size, your only option is more JPEG compression. Do this using ‘Save for the web’, not using ‘Save as’, because ‘Save as’ will keep extra data such as EXIF headers and that will also make files larger than needed for the web.


Johan W. Elzenga johan<<at>>johanfoto.nl Editor / Photographer http://www.johanfoto.nl/
V
Voivod
Sep 25, 2004
On 24 Sep 2004 14:32:40 -0700, (Steve Holmes)
scribbled:

How do I reduce 300 dpi .jpgs or .gifs to 72 dpi in Photoshop while keeping them the same size on the screen?

For example, say the file is 1024 x 768 at 300 dpi (178 kb). Through "Image Size," I change the resolution to 72, but the picture shrinks to around
247 x 184. Well, I want it at the original screen size, just at a lower dpi. When I restore the pixel width to 1024, while keeping it at 72 dpi, the print dimensions balloon way out so that the file is as huge as when I started. "Save for web" doesn’t help. By the way, do you save website .jpgs as "High?"

I don’t expect to be printing these, but am working with copies of the original files just in case.

For education purposes: Here’s two images, they’re both the same pixel dimension, they’re both the same byte size. One’s saved at 5 DPI the other at 5000 DPI. You cannot tell the difference since DPI only applies when PRINTING.
http://s90011794.onlinehome.us/pixels/
S
Scraphead
Sep 26, 2004
geez, Voivod, are those tattoos on you?

"Voivod" wrote in message
On 24 Sep 2004 14:32:40 -0700, (Steve Holmes)
scribbled:

How do I reduce 300 dpi .jpgs or .gifs to 72 dpi in Photoshop while keeping them the same size on the screen?

For example, say the file is 1024 x 768 at 300 dpi (178 kb). Through "Image Size," I change the resolution to 72, but the picture shrinks to around
247 x 184. Well, I want it at the original screen size, just at a lower dpi. When I restore the pixel width to 1024, while keeping it at 72 dpi, the print dimensions balloon way out so that the file is as huge as when I started. "Save for web" doesn’t help. By the way, do you save website .jpgs as "High?"

I don’t expect to be printing these, but am working with copies of the original files just in case.

For education purposes: Here’s two images, they’re both the same pixel dimension, they’re both the same byte size. One’s saved at 5 DPI the other at 5000 DPI. You cannot tell the difference since DPI only applies when PRINTING.
http://s90011794.onlinehome.us/pixels/
U
Uni
Sep 26, 2004
Voivod wrote:
On 24 Sep 2004 14:32:40 -0700, (Steve Holmes)
scribbled:

How do I reduce 300 dpi .jpgs or .gifs to 72 dpi in Photoshop while keeping them the same size on the screen?

For example, say the file is 1024 x 768 at 300 dpi (178 kb). Through "Image Size," I change the resolution to 72, but the picture shrinks to around
247 x 184. Well, I want it at the original screen size, just at a lower dpi. When I restore the pixel width to 1024, while keeping it at 72 dpi, the print dimensions balloon way out so that the file is as huge as when I started. "Save for web" doesn’t help. By the way, do you save website .jpgs as "High?"

I don’t expect to be printing these, but am working with copies of the original files just in case.

For education purposes: Here’s two images, they’re both the same pixel dimension, they’re both the same byte size. One’s saved at 5 DPI the other at 5000 DPI. You cannot tell the difference since DPI only applies when PRINTING.

Not so true. Most people in usenet believe that. However, some image viewers will change what you see on the screen, if you change the aspect ratio resolution of the image.

Uni

http://s90011794.onlinehome.us/pixels/
N
nomail
Sep 26, 2004
Uni wrote:

For education purposes: Here’s two images, they’re both the same pixel dimension, they’re both the same byte size. One’s saved at 5 DPI the other at 5000 DPI. You cannot tell the difference since DPI only applies when PRINTING.

Not so true. Most people in usenet believe that. However, some image viewers will change what you see on the screen, if you change the aspect ratio resolution of the image.

Some programs may display an image at a different enlargement if the resolution is different, but that does not make the images different. They are identical in size, no matter what program you use.

BTW, I know what the resolution is, and I know what the aspect ratio is. But what is the "aspect ratio resolution"?


Johan W. Elzenga johan<<at>>johanfoto.nl Editor / Photographer http://www.johanfoto.nl/
U
Uni
Sep 26, 2004
Johan W. Elzenga wrote:
Uni wrote:

For education purposes: Here’s two images, they’re both the same pixel dimension, they’re both the same byte size. One’s saved at 5 DPI the other at 5000 DPI. You cannot tell the difference since DPI only applies when PRINTING.

Not so true. Most people in usenet believe that. However, some image viewers will change what you see on the screen, if you change the aspect ratio resolution of the image.

Some programs may display an image at a different enlargement if the resolution is different, but that does not make the images different. They are identical in size, no matter what program you use.

Agreed.

BTW, I know what the resolution is, and I know what the aspect ratio is. But what is the "aspect ratio resolution"?

In other words, the X & Y JPEG resolution values can differ, such as 300 x 200 DPI.

Uni
N
nomail
Sep 26, 2004
Uni wrote:

BTW, I know what the resolution is, and I know what the aspect ratio is. But what is the "aspect ratio resolution"?

In other words, the X & Y JPEG resolution values can differ, such as 300 x 200 DPI.

No, they can’t. A scanner can have different resolutions on each axis, but a file cannot have that. You can have 300 x 200 *pixels*, but you cannot have 300 x 200 *dpi*.


Johan W. Elzenga johan<<at>>johanfoto.nl Editor / Photographer http://www.johanfoto.nl/
U
Uni
Sep 26, 2004
Johan W. Elzenga wrote:
Uni wrote:

BTW, I know what the resolution is, and I know what the aspect ratio is. But what is the "aspect ratio resolution"?

In other words, the X & Y JPEG resolution values can differ, such as 300 x 200 DPI.

No, they can’t. A scanner can have different resolutions on each axis, but a file cannot have that. You can have 300 x 200 *pixels*, but you cannot have 300 x 200 *dpi*.

The problem is, you typically see one value in Photoshop. It ASSUMES both X & Y values are the same. However, you can manually change either to whatever pleases your heart. So, yes, you can even have 300 x 001, if you wish.

Uni
U
Uni
Sep 26, 2004
Uni wrote:
Johan W. Elzenga wrote:

Uni wrote:

BTW, I know what the resolution is, and I know what the aspect ratio is.
But what is the "aspect ratio resolution"?

In other words, the X & Y JPEG resolution values can differ, such as 300 x 200 DPI.

No, they can’t. A scanner can have different resolutions on each axis, but a file cannot have that. You can have 300 x 200 *pixels*, but you cannot have 300 x 200 *dpi*.

The problem is, you typically see one value in Photoshop. It ASSUMES both X & Y values are the same. However, you can manually change either to whatever pleases your heart. So, yes, you can even have 300 x 001, if you wish.

Uni

p.s. And it is not known as "resolution", but "density" per the JPEG File Exchange Format, v 1.02, dated September 1, 1992.

I bet you didn’t know that the unit values can be dots per inch or dots per cm.

Uni
U
Uni
Sep 26, 2004
Uni wrote:
Uni wrote:

Johan W. Elzenga wrote:

Uni wrote:

BTW, I know what the resolution is, and I know what the aspect ratio is.
But what is the "aspect ratio resolution"?

In other words, the X & Y JPEG resolution values can differ, such as 300
x 200 DPI.

No, they can’t. A scanner can have different resolutions on each axis, but a file cannot have that. You can have 300 x 200 *pixels*, but you cannot have 300 x 200 *dpi*.

The problem is, you typically see one value in Photoshop. It ASSUMES both X & Y values are the same. However, you can manually change either to whatever pleases your heart. So, yes, you can even have 300 x 001, if you wish.

Uni

p.s. And it is not known as "resolution", but "density" per the JPEG File Exchange Format, v 1.02, dated September 1, 1992.

I bet you didn’t know that the unit values can be dots per inch or dots per cm.

Uni

p.p.s. "Exchange" should be "Interchange".

🙂

Uni
S
sigerson
Sep 27, 2004
(snip)
If you want
to keep the same number of pixels but at a smaller file size, your only option is more JPEG compression.

Thanks for the help, everyone — especially Johan. I’ve been using Photoshop’s preset of "High" when saving for the web. Can I go lower and keep the same quality?


Steve Holmes
Executive Producer
"The New Ball Game"
"RailFAN"

Must-have mockup pack for every graphic designer 🔥🔥🔥

Easy-to-use drag-n-drop Photoshop scene creator with more than 2800 items.

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