Changing DPI

Freddie59

Hope someone can help. I'm trying to change the resolution of a photo from 72dpi (which it was saved at) to 300dpi. The problem is that the file size becomes absolutely huge.

Anyone any suggestions?:)

stcstc

the term is PPI not DPI


DPI is a print term PPI if to do with a file

when you change to 300 your adding more pixels so the file will be bigger

it also depends on the size of print you are trying to achieve

AnCatDubh

as steve says above, but its slightly irrelevant (well its not but in a particular context it is, if i haven't already confused myself by what i'm saying).

if you have an image which has 6000 x 4000 pixels then if using 72dpi (ppi) your print size will be the number of pixels divided by the dpi / ppi here 72 = 83.33inches x 55.55inches. The exact same image 6000 x 4000 pixels in the context of 300dpi (ppi) = 20inches x 13.33inches. Same dimensions - just different divisor.

You won't use 72dpi for print - probably more from 200dpi upwards (300 is often quoted but it will depend on the printer being used and what its technical requirements are).

So what might be more useful to you is to look at the number of pixels in your image (width x height) and divide it by the number of dpi that your printer is expecting, which will give an indication as to the number of inch height and width that you can expect from your current image. Beyond that you are scaling / resizing the image which may be necessary if you haven't enough pixels in the first place.

Freddie59

Thanks for the answers folks. I suppose I'm totally confused! I usually only save the photos to PC or to Flickr/Panoramio (very rarely print) but a competition I'm entering requires the file size to be 3MB max with 300dpi.

Does that help? If so, what adjustments should I make (I can use CS3 on a friend's PC. Used to have PS on the old PC, but not on the Mac).

Thanks again.

Freddie.

stcstc

make it 300 dpi and save as jpg to bring it down to 3mb

stunt_penguin

okay, ignoring the whole compication of comparing sizes and resolutions

1- open your image in whatever version of photoshop you happen to be using.

2 - hit image-> resize

3 - in the resize image dialogue there will be a 'resample image' checkbox (it's either resize/resample image from memory) - uncheck this box so that PS does not change the number of pixels in your image, only how many dots-per-inch your image is.

4 - change the value for dpi in the textbox, and you will see th at the number of pixels in the image stays the same, but the dimensions in cm do change.

hit ok, and then save your image out as a JPEG , ensuring that the compression is sufficient to give you a 3mb file, but not too high as to give you compression artefacts. about '80' or a 9 out of 12 in Photoshop will be about right.

I really need to do a video demo on resolution as it pertains to digital photos,....... to be honest I doubt that the resolution of the file matters in the OP's case- DPI is a very old fashioned way of specifying h ow large to make an image- it's the actual pixel count that matters-


I wrote a competition system for the Federation of European photographers before now and the only stipulation I made was on pixel count on the longest side plus the file size... I wanted i mages at least 1,200 pixels on the longest side and under 3mb..... dpi never ever, ever ever matters on screen as the image is either displayed at 100% scale or squished to fit the screen in some way.

The dpi settting (it's only a piece of metadata) of an image almost never matters in print either, as the image you supply will be scaled to fit the medium regardless of the setting. There are optimum resolutions and pixel counts for different printers but that matters little in normal situations.

Freddie59

stunt_penguin wrote: »

okay, ignoring the whole compication of comparing sizes and resolutions

1- open your image in whatever version of photoshop you happen to be using.

2 - hit image-> resize

3 - in the resize image dialogue there will be a 'resample image' checkbox (it's either resize/resample image from memory) - uncheck this box so that PS does not change the number of pixels in your image, only how many dots-per-inch your image is.

4 - change the value for dpi in the textbox, and you will see th at the number of pixels in the image stays the same, but the dimensions in cm do change.

hit ok, and then save your image out as a JPEG , ensuring that the compression is sufficient to give you a 3mb file, but not too high as to give you compression artefacts. about '80' or a 9 out of 12 in Photoshop will be about right.

I really need to do a video demo on resolution as it pertains to digital photos,....... to be honest I doubt that the resolution of the file matters in the OP's case- DPI is a very old fashioned way of specifying h ow large to make an image- it's the actual pixel count that matters-


I wrote a competition system for the Federation of European photographers before now and the only stipulation I made was on pixel count on the longest side plus the file size... I wanted i mages at least 1,200 pixels on the longest side and under 3mb..... dpi never ever, ever ever matters on screen as the image is either displayed at 100% scale or squished to fit the screen in some way.

The dpi settting (it's only a piece of metadata) of an image almost never matters in print either, as the image you supply will be scaled to fit the medium regardless of the setting. There are optimum resolutions and pixel counts for different printers but that matters little in normal situations.

Thanks for all the help everyone.:)

Freddie.

Cameraman

Freddie59 wrote: »

Thanks for the answers folks. I suppose I'm totally confused! I usually only save the photos to PC or to Flickr/Panoramio (very rarely print) but a competition I'm entering requires the file size to be 3MB max with 300dpi.

Are you doing a print or a digital file ?
Digital files don't have a dpi (or ppi) - so 300dpi, on its own, is meaningless.

OTOH, if they specifiy a print size e.g. 10"x8" @300dpi then you would need to size your file at 3000x2400. As I said, DPI values without print sizes are meaningless.

Freddie59

Cameraman wrote: »

Are you doing a print or a digital file ?
Digital files don't have a dpi (or ppi) - so 300dpi, on its own, is meaningless.

OTOH, if they specifiy a print size e.g. 10"x8" @300dpi then you would need to size your file at 3000x2400. As I said, DPI values without print sizes are meaningless.

Just a digital file to be emailed (3MB max, 300dpi).

Cameraman

Freddie59 wrote: »

Just a digital file to be emailed (3MB max, 300dpi).

OK - right. In that case the main thing is the 3MB file size - the 300 dpi is irrelevant and misleading (but often misused/misquoted/misunderstood).

The relevant items for digital files are :

Dimension in pixels e.g. 900 x 600 px
File Size e.g. 3MB
JPEG save quality (e.g. Photoshop level 10)

Third Eye

I think the easiest way to achieve what you want (in photoshop).

Open image. On main menu bar at the top of programme go to Image
Then Image Size which opens dialogue box. Make sure that Re-sample image is unchecked. Change your ppi to 300 pixels per inch. Your file size will remain the same and if saved as a jpeg it will probably be under the 3mb. If you want to email me the file I can do it for you.

Cameraman

Yes - but why go to all that bother when it doesn't actually do anything

stcstc

because thats what the client is asking for

although it doesnt matter, its what is being asked for

Cameraman

stcstc wrote: »

because thats what the client is asking for

although it doesnt matter, its what is being asked for

Yeah - but the client here is asking for something that doesn't exist - so how can you give it to him