PNG format & DPI

"Jon" wrote in message

If I scan an image at 600 DPI and save it as a Tiff the resolution (as displayed in Bridge) is, as I would expect it to be: 600 DPI. However, if I save it as a PNG the resolution drops to 72 DPI! Is there a way to change this?

Pixel density(resolution) is irrelevant, pixel dimensions are what is important.
Example, if you scan a 10×8 inch image at 600 dpi, you will have an image with a pixel dimension of 6000×4800 pixels.(10 x 8 at 600ppi) If this is then viewed/reduced to 72 ppi, you still have a 6000×4800 image (unless resampled) but instead of being 10×8 it is now 83.3 x 66.7 inches. (600/72) x 10&8
PNG’s are usually used in web design work where transparency and scalability are important and as such 72ppi (screen resolution) is adequate for this application.
Unless your pixel dimensions (not resolution) are reducing accordingly, you have nothing to worry about.

TWK

Toobi-Won Kenobi wrote:

"Jon" wrote in message

If I scan an image at 600 DPI and save it as a Tiff the resolution (as displayed in Bridge) is, as I would expect it to be: 600 DPI. However, if I save it as a PNG the resolution drops to 72 DPI! Is there a way to change this?

Pixel density(resolution) is irrelevant, pixel dimensions are what is important.
Example, if you scan a 10×8 inch image at 600 dpi, you will have an image with a pixel dimension of 6000×4800 pixels.(10 x 8 at 600ppi) If this is then viewed/reduced to 72 ppi, you still have a 6000×4800 image (unless resampled) but instead of being 10×8 it is now 83.3 x 66.7 inches. (600/72) x 10&8
PNG’s are usually used in web design work where transparency and scalability are important and as such 72ppi (screen resolution) is adequate for this application.
Unless your pixel dimensions (not resolution) are reducing accordingly, you have nothing to worry about.

TWK

Thanks, but I’m still not clear on what’s happening here. OK, so I scan a 7" x 5" photo straight into PS at 600dpi. Before I save it I check Image Size which tells me that I have the following:
Pixel dimensions: 4200 x 3000
Document size: 7" x 5"
Resolution: 600DPI

Saved it as a TIFF Bridge shows it as:
Pixel dimensions: 4200 x 3000
Document size: 7" x 5"
Resolution: 600DPI

Saved as a PNG Bridge shows it as:
Pixel dimensions: 4200 x 3000
Document size: 7" x 5"
Resolution: 72DPI

If I open both photos in PS and check Image Size they both state: Pixel dimensions: 4200 x 3000
Document size: 7" x 5"
Resolution: 600DPI

So what’s happening in Bridge? Why is it displaying a different DPI?

Jon

"Jon" wrote in message

Toobi-Won Kenobi wrote:

"Jon" wrote in message

If I scan an image at 600 DPI and save it as a Tiff the resolution (as displayed in Bridge) is, as I would expect it to be: 600 DPI. However, if I save it as a PNG the resolution drops to 72 DPI! Is there a way to change this?

Pixel density(resolution) is irrelevant, pixel dimensions are what is important.
Example, if you scan a 10×8 inch image at 600 dpi, you will have an image with a pixel dimension of 6000×4800 pixels.(10 x 8 at 600ppi) If this is then viewed/reduced to 72 ppi, you still have a 6000×4800 image (unless resampled) but instead of being 10×8 it is now 83.3 x 66.7 inches.
(600/72) x 10&8
PNG’s are usually used in web design work where transparency and scalability are important and as such 72ppi (screen resolution) is adequate for this application.
Unless your pixel dimensions (not resolution) are reducing accordingly, you have nothing to worry about.

TWK

Thanks, but I’m still not clear on what’s happening here. OK, so I scan a 7" x 5" photo straight into PS at 600dpi. Before I save it I check Image Size which tells me that I have the following:
Pixel dimensions: 4200 x 3000
Document size: 7" x 5"
Resolution: 600DPI

Saved it as a TIFF Bridge shows it as:
Pixel dimensions: 4200 x 3000
Document size: 7" x 5"
Resolution: 600DPI

Saved as a PNG Bridge shows it as:
Pixel dimensions: 4200 x 3000
Document size: 7" x 5"
Resolution: 72DPI

If I open both photos in PS and check Image Size they both state: Pixel dimensions: 4200 x 3000
Document size: 7" x 5"
Resolution: 600DPI

So what’s happening in Bridge? Why is it displaying a different DPI?

Jon,

Why are you saving it as a PNG? As I said, PNG’s are used primarily for web work which is (obviously) displayed on a monitior, usually at 72 ppi..If you are doing web work, there is no need to scan at such a high res. The fact that you can display both images in PS at your scan resolution suggests that Bridge (which I don’t use) is only showing you what you what you would get on your webpage. After all, there are not many monitors that can display a 58.3 x 41.7 inch image. (4200×3000 at 72ppi). What does it show equivalent JPGs, etc., at?
I wouldn’t lose any sleep over it.
TWK

Toobi-Won Kenobi wrote:

"Jon" wrote in message

Toobi-Won Kenobi wrote:

"Jon" wrote in message

If I scan an image at 600 DPI and save it as a Tiff the resolution (as displayed in Bridge) is, as I would expect it to be: 600 DPI. However, if I save it as a PNG the resolution drops to 72 DPI! Is there a way to change this?

Pixel density(resolution) is irrelevant, pixel dimensions are what is important.
Example, if you scan a 10×8 inch image at 600 dpi, you will have an image with a pixel dimension of 6000×4800 pixels.(10 x 8 at 600ppi) If this is then viewed/reduced to 72 ppi, you still have a 6000×4800 image (unless resampled) but instead of being 10×8 it is now 83.3 x 66.7 inches.
(600/72) x 10&8
PNG’s are usually used in web design work where transparency and scalability are important and as such 72ppi (screen resolution) is adequate for this application.
Unless your pixel dimensions (not resolution) are reducing accordingly, you have nothing to worry about.

TWK

Thanks, but I’m still not clear on what’s happening here. OK, so I scan a 7" x 5" photo straight into PS at 600dpi. Before I save it I check Image Size which tells me that I have the following:
Pixel dimensions: 4200 x 3000
Document size: 7" x 5"
Resolution: 600DPI

Saved it as a TIFF Bridge shows it as:
Pixel dimensions: 4200 x 3000
Document size: 7" x 5"
Resolution: 600DPI

Saved as a PNG Bridge shows it as:
Pixel dimensions: 4200 x 3000
Document size: 7" x 5"
Resolution: 72DPI

If I open both photos in PS and check Image Size they both state: Pixel dimensions: 4200 x 3000
Document size: 7" x 5"
Resolution: 600DPI

So what’s happening in Bridge? Why is it displaying a different DPI?

Jon,

Why are you saving it as a PNG? As I said, PNG’s are used primarily for web work which is (obviously) displayed on a monitior, usually at 72 ppi..If you are doing web work, there is no need to scan at such a high res. The fact that you can display both images in PS at your scan resolution suggests that Bridge (which I don’t use) is only showing you what you what you would get on your webpage. After all, there are not many monitors that can display a 58.3 x 41.7 inch image. (4200×3000 at 72ppi). What does it show equivalent JPGs, etc., at?
I wouldn’t lose any sleep over it.
TWK

Why are you saving it as a PNG?

OK, I convert some images to PNG in order to upload them to Flickr (http://www.flickr.com/photos/skepsis/).
Now, I believe that Flickr accepts TIFFs but there is an upload limit on file size (10mb). So since PNG is lossless I use it to reduce my original file sizes.

I usually scan at 600 DPI as this allows me to crop the image if required and still have a reasonable pixel dimension and hence, larger prints when I send the images off for printing.

If I scan at 72DPI the image dimensions come out at 504 x 360 pixels and in Bridge this shows 72DPI. In fact, whatever DPI I scan at, when saved as a PNG, Bridge shows 72DPI (even if I scan at 50DPI) whereas Photoshop (Image Size) always shows the actual DPI.

With JPGs there is no discrepancy between Bridge and PS. Oh, I won’t lose sleep over it, I’m just curious as to why this happens with PNGs and Bridge.

Jon

"Jon" wrote in message

Toobi-Won Kenobi wrote:

"Jon" wrote in message

Toobi-Won Kenobi wrote:

"Jon" wrote in message

If I scan an image at 600 DPI and save it as a Tiff the resolution (as displayed in Bridge) is, as I would expect it to be: 600 DPI. However, if I save it as a PNG the resolution drops to 72 DPI! Is there a way to change this?

Pixel density(resolution) is irrelevant, pixel dimensions are what is important.
Example, if you scan a 10×8 inch image at 600 dpi, you will have an image with a pixel dimension of 6000×4800 pixels.(10 x 8 at 600ppi) If this is then viewed/reduced to 72 ppi, you still have a 6000×4800 image (unless resampled) but instead of being 10×8 it is now 83.3 x 66.7 inches.
(600/72) x 10&8
PNG’s are usually used in web design work where transparency and scalability are important and as such 72ppi (screen resolution) is adequate for this application.
Unless your pixel dimensions (not resolution) are reducing accordingly, you have nothing to worry about.

TWK

Thanks, but I’m still not clear on what’s happening here. OK, so I scan a 7" x 5" photo straight into PS at 600dpi. Before I save it I check Image Size which tells me that I have the following:
Pixel dimensions: 4200 x 3000
Document size: 7" x 5"
Resolution: 600DPI

Saved it as a TIFF Bridge shows it as:
Pixel dimensions: 4200 x 3000
Document size: 7" x 5"
Resolution: 600DPI

Saved as a PNG Bridge shows it as:
Pixel dimensions: 4200 x 3000
Document size: 7" x 5"
Resolution: 72DPI

If I open both photos in PS and check Image Size they both state: Pixel dimensions: 4200 x 3000
Document size: 7" x 5"
Resolution: 600DPI

So what’s happening in Bridge? Why is it displaying a different DPI?

Jon,

Why are you saving it as a PNG? As I said, PNG’s are used primarily for web work which is (obviously) displayed on a monitior, usually at 72 ppi..If you are doing web work, there is no need to scan at such a high res.
The fact that you can display both images in PS at your scan resolution suggests that Bridge (which I don’t use) is only showing you what you what you would get on your webpage. After all, there are not many monitors that can display a 58.3 x 41.7 inch image. (4200×3000 at 72ppi). What does it show equivalent JPGs, etc., at?
I wouldn’t lose any sleep over it.
TWK

Why are you saving it as a PNG?

OK, I convert some images to PNG in order to upload them to Flickr (http://www.flickr.com/photos/skepsis/).
Now, I believe that Flickr accepts TIFFs but there is an upload limit on file size (10mb). So since PNG is lossless I use it to reduce my original file sizes.

I usually scan at 600 DPI as this allows me to crop the image if required and still have a reasonable pixel dimension and hence, larger prints when I send the images off for printing.

If I scan at 72DPI the image dimensions come out at 504 x 360 pixels and in Bridge this shows 72DPI. In fact, whatever DPI I scan at, when saved as a PNG, Bridge shows 72DPI (even if I scan at 50DPI) whereas Photoshop (Image Size) always shows the actual DPI.

With JPGs there is no discrepancy between Bridge and PS. Oh, I won’t lose sleep over it, I’m just curious as to why this happens with PNGs and Bridge.

Jon,

Bridge is obviously showing you how the image would look when uploaded to a webpage and giving you the opportunity to view the quality. I have used online photo sites over the years, and have never had any problem (quality wise) using JPG’s. Any loss of quality due to the compression can be suffered by anybody who wants to "borrow" the images for their own use. 😉

TWK

Toobi-Won Kenobi wrote:

"Jon" wrote in message

Toobi-Won Kenobi wrote:

"Jon" wrote in message

Toobi-Won Kenobi wrote:

"Jon" wrote in message

If I scan an image at 600 DPI and save it as a Tiff the resolution (as displayed in Bridge) is, as I would expect it to be: 600 DPI. However, if I save it as a PNG the resolution drops to 72 DPI! Is there a way to change this?

Pixel density(resolution) is irrelevant, pixel dimensions are what is important.
Example, if you scan a 10×8 inch image at 600 dpi, you will have an image with a pixel dimension of 6000×4800 pixels.(10 x 8 at 600ppi) If this is then viewed/reduced to 72 ppi, you still have a 6000×4800 image (unless resampled) but instead of being 10×8 it is now 83.3 x 66.7 inches.
(600/72) x 10&8
PNG’s are usually used in web design work where transparency and scalability are important and as such 72ppi (screen resolution) is adequate for this application.
Unless your pixel dimensions (not resolution) are reducing accordingly, you have nothing to worry about.

TWK

Thanks, but I’m still not clear on what’s happening here. OK, so I scan a 7" x 5" photo straight into PS at 600dpi. Before I save it I check Image Size which tells me that I have the following:
Pixel dimensions: 4200 x 3000
Document size: 7" x 5"
Resolution: 600DPI

Saved it as a TIFF Bridge shows it as:
Pixel dimensions: 4200 x 3000
Document size: 7" x 5"
Resolution: 600DPI

Saved as a PNG Bridge shows it as:
Pixel dimensions: 4200 x 3000
Document size: 7" x 5"
Resolution: 72DPI

If I open both photos in PS and check Image Size they both state: Pixel dimensions: 4200 x 3000
Document size: 7" x 5"
Resolution: 600DPI

So what’s happening in Bridge? Why is it displaying a different DPI?

Jon,

Why are you saving it as a PNG? As I said, PNG’s are used primarily for web work which is (obviously) displayed on a monitior, usually at 72 ppi..If you are doing web work, there is no need to scan at such a high res.
The fact that you can display both images in PS at your scan resolution suggests that Bridge (which I don’t use) is only showing you what you what you would get on your webpage. After all, there are not many monitors that can display a 58.3 x 41.7 inch image. (4200×3000 at 72ppi). What does it show equivalent JPGs, etc., at?
I wouldn’t lose any sleep over it.
TWK

Why are you saving it as a PNG?

OK, I convert some images to PNG in order to upload them to Flickr (http://www.flickr.com/photos/skepsis/).
Now, I believe that Flickr accepts TIFFs but there is an upload limit on file size (10mb). So since PNG is lossless I use it to reduce my original file sizes.

I usually scan at 600 DPI as this allows me to crop the image if required and still have a reasonable pixel dimension and hence, larger prints when I send the images off for printing.

If I scan at 72DPI the image dimensions come out at 504 x 360 pixels and in Bridge this shows 72DPI. In fact, whatever DPI I scan at, when saved as a PNG, Bridge shows 72DPI (even if I scan at 50DPI) whereas Photoshop (Image Size) always shows the actual DPI.

With JPGs there is no discrepancy between Bridge and PS. Oh, I won’t lose sleep over it, I’m just curious as to why this happens with PNGs and Bridge.

Jon,

Bridge is obviously showing you how the image would look when uploaded to a webpage and giving you the opportunity to view the quality. I have used online photo sites over the years, and have never had any problem (quality wise) using JPG’s. Any loss of quality due to the compression can be suffered by anybody who wants to "borrow" the images for their own use. 😉

TWK

OK. Thanks for your comments

Jon