PPI effect on print size?

Robbo

Robbo

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Getting confused yet again....

Basically, the main question is, what is the best setting for PPI when converting from raw to tiff/jpeg etc....

I have tried 150, 240 and 300. None effect the actual pixel size of the picture, but seems to have an effect on the document/print size. And it seems to be backwards...... e.g. 150 gives me a bigger print, 240 smaller, and 300 even smaller again. This is using the 'Print Size' button in CS4.

Now I am confused.

If some one can tell me in thicko terms how PPI has an effect on the picture, if any, and what the 'standard' should be from conversion of raw.

Thanks again.!
:thumbs:
 
Robbo said:
Getting confused yet again....

Basically, the main question is, what is the best setting for PPI when converting from raw to tiff/jpeg etc....

I have tried 150, 240 and 300. None effect the actual pixel size of the picture, but seems to have an effect on the document/print size. And it seems to be backwards...... e.g. 150 gives me a bigger print, 240 smaller, and 300 even smaller again. This is using the 'Print Size' button in CS4.

Now I am confused.

If some one can tell me in thicko terms how PPI has an effect on the picture, if any, and what the 'standard' should be from conversion of raw.

Thanks again.!
:thumbs:
Click to expand...

What you are doing is leaving resample switched on. You are changing the size of the image so that the print size remains consistent.

Look at the number of pixels in the image.

If the number remains the same and only the ppi value changes, that will change only the phyisical print.

So in "Image Size" turn off resample and now you are free to change the ppi value.

An equation I use

Ps = Px/R

Where Ps is the print size, Px is the number of pixels along a single axis and R isd the resolution.

If I have an 1800x1200px image I know that it's a 6x4 @ 300ppi

Do the calc for each axis
Ps = 1800/300 = 6
Ps = 1200/300 = 4

Now if I want to printg at 150ppi

1800/150 = 12
1200/150 = 8

So half the resolution will give double the print size.

Don't resample.
 
Thanks for the replies, it's slowly sinking in.

So, am I best to just leave the ppi at a 'standard' e.g 240

Or do I need to change the ppi depending on what size I am sending off for print?

Also, say I set it to 300ppi it will be say 7x5 inch print, if I wanted a big print over that size won't it naturally spread the pixels out making it the same as say a 200ppi set image?

Can of worms lol
 
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It will depend on the printers. DSCL (for example) print at 300ppi. They totally ignore what you gave set for "dpi". Give them an image that is 3000x3000 and it'll come back 10" square, no matter what your dpi/ppi setting is.
 
Robbo said:
Thanks for the replies, it's slowly sinking in.

So, am I best to just leave the ppi at a 'standard' e.g 240

Or do I need to change the ppi depending on what size I am sending off for print?

Also, say I set it to 300ppi it will be say 7x5 inch print, if I wanted a big print over that size won't it naturally spread the pixels out making it the same as say a 200ppi set image?

Can of worms lol
Click to expand...

It really does not matter as all labs will automaticly alter the ppi to suit the printing machine they are using.



As for home ink jet printing 240ppi is considered the norm, but even this is not critical as the printer driver will alter the ppi if you change the output size in the printing software/photoshop.

So to sum up a digital image does not have a physical size until it is printed and so any ppi you set is arbitary till then.:)
 
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right, so basically I dont really need to mess about with PPI as its not going to make any difference as the print companies are going to change it anyway?

Am I best to just keep it set to 300?
 
arad85 said:
It will depend on the printers. DSCL (for example) print at 300ppi. They totally ignore what you gave set for "dpi". Give them an image that is 3000x3000 and it'll come back 10" square, no matter what your dpi/ppi setting is.
Click to expand...

That's a bad show from a printer if they do that. I would not want to send my images to them if that was the case. I regularly send images at lower ppi (not dpi) values to my lab.

If I set the size to 20x20 and send a 3000 x 3000 @ 150ppi, then IU expect it to be printed at 20x20. The image should still be printed at 300dpi (note DPI) because dpi is a printer resolution setting. It will lay down 300 dots per inch on the paper. But the image I sent is still 150ppi.
 
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Robbo said:
Thanks for the replies, it's slowly sinking in.

So, am I best to just leave the ppi at a 'standard' e.g 240

Or do I need to change the ppi depending on what size I am sending off for print?

Also, say I set it to 300ppi it will be say 7x5 inch print, if I wanted a big print over that size won't it naturally spread the pixels out making it the same as say a 200ppi set image?

Can of worms lol
Click to expand...

It does depend on who you send the images to. I'm quite sure your lab will print a 240ppi image at the size you need but you may need to provide a note when submitting it. Just size it correctly. 10x10 @ 240ppi gives an image that is 2400 x 2400 - The print will then be printed at the printers standard resolution that is 300dpi. So I leave mine at the default setting and use their Remote Online Entry System.

If you want to send a 7x5 @300ppi that is a pretty small image only 2100 x 1500pixels.

If you want a larger print from that same file yes easy but the ppi will fall.

What I will add is that smaller images require a larger ppi value than larger images. The further away you view the image, the less important ppi becomes. Look at billboards. Typically lower than 20ppi

Hence if you print a 20x16 image you woun't look at it from 6" as you would a 7xor 10x8. It would be looked at from a few feet and your eye can't pick out such small detail at those distances.

There's a lot of info on te web regards this. - although yes some misinformation too :)
 
OlyPaul said:
No he is not, read his post again, he is not changing the pixel dimensions but the ppi .:)
Click to expand...

He was resampling.

He said the print size was remaining the same when he changed the ppi value - that means the image was being resampled because with resampling off the print size would have changed.

Cheers
JD
 
OlyPaul said:
It really does not matter as all labs will automaticly alter the ppi to suit the printing machine they are using.



As for home ink jet printing 240ppi is considered the norm, but even this is not critical as the printer driver will alter the ppi if you change the output size in the printing software/photoshop.

So to sum up a digital image does not have a physical size until it is printed and so any ppi you set is arbitary till then.:)
Click to expand...

The lab should not alter your ppi value. The printing machine prints in DPI images are sent in ppi - the two values are totally different.

The home printer driver DOES NOT alter the ppi value of your image - it only changes the amount of ink based on the quality you set in the driver. So you can send a 300ppi print at normal setting and it will probably be poor

Or send it at a higher quality setting and you'll get what you want.... The ppi value of the image has not changed.

JD
 
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EOS_JD said:
He was resampling.

He said the print size was remaining the same when he changed the ppi value - that means the image was being resampled because with resampling off the print size would have changed.

Cheers
JD
Click to expand...

Read it again .;)

I have tried 150, 240 and 300. None effect the actual pixel size of the picture, but seems to have an effect on the document/print size. And it seems to be backwards...... e.g. 150 gives me a bigger print, 240 smaller, and 300 even smaller again.
Click to expand...

If the pixel size (dimensions) is not changing but the document size is then it is not being resampled. :)
 
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Robbo said:
Getting confused yet again....

Basically, the main question is, what is the best setting for PPI when converting from raw to tiff/jpeg etc....

I have tried 150, 240 and 300. None effect the actual pixel size of the picture, but seems to have an effect on the document/print size. And it seems to be backwards...... e.g. 150 gives me a bigger print, 240 smaller, and 300 even smaller again. This is using the 'Print Size' button in CS4.

Now I am confused.

If some one can tell me in thicko terms how PPI has an effect on the picture, if any, and what the 'standard' should be from conversion of raw.

Thanks again.!
:thumbs:
Click to expand...

Don't know how I misread your post :) So sorry! You were not rersampling and what you have is correct.

The reason that higher ppi images are smaller is that you are reducing the size of the pixels.

a pixel in an image at 150ppi is twixe the size it would be if printed at 300ppi. So a 150ppi print will be double the size of a 300ppi image. You are cramming the same number of prints into a smaller area.
 
Starting from the start!

ppi stands for pixels per inch. You can calculate the resolution of a printed picture by dividing the number of pixels across by the width of the picture (or by dividing the number of pixels down by the height of the picture)

Any picture that you have will be a certain number of pixels across and a certain number of pixels down. For example a picture could be 3000 pixels by 2100 pixels.

When you print the picture it will have a certain physical size, for example 10 inches by 7 inches.

Therefore that printed picture will have 300 pixels in every inch across and in every inch down, i.e. it has a resolution of 300ppi. (3000pixels across divided by 10 inches across, or 2100 pixels down divided by 7 inches down)

If you have resampling off and change the resolution from 300ppi to 150ppi then you have 3000 pixels divided by 150 so the printed picture will be 20 inches across and 14 inches down (2100 pixels divided by 150)

Some PP programs still use the term dpi instead of ppi. This can be confusing because when you print you can also set your printer to spray a certain number of dots per inch (dpi) & this has nothing to do with the ppi/dpi figure in the PP program.

For example I can print a picture at 300ppi, which determines the physical size of the printout and at 600dpi which means that my printer sprays 2 dots for each pixel.
 
EOS_JD said:
That's a bad show from a printer if they do that. I would not want to send my images to them if that was the case. I regularly send images at lower ppi (not dpi) values to my lab.

If I set the size to 20x20 and send a 3000 x 3000 @ 150ppi, then IU expect it to be printed at 20x20. The image should still be printed at 300dpi (note DPI) because dpi is a printer resolution setting. It will lay down 300 dots per inch on the paper. But the image I sent is still 150ppi.
Click to expand...
I think printing at a specific ppi is what you would expect of a photo printers. I'd far rather do the resize myself rather than leave any resampling down to the printer. It avoids any issues of quality expectations IMHO.
 
arad85 said:
I think printing at a specific ppi is what you would expect of a photo printers. I'd far rather do the resize myself rather than leave any resampling down to the printer. It avoids any issues of quality expectations IMHO.
Click to expand...

No they print at a specific dpi. To be honest their RIPs will do a better job when they need to resample.
 
Suvv said:
Suvv said:
When you print the picture it will have a certain physical size, for example 10 inches by 7 inches.
Click to expand...

I'd say when you print it it would have a specified resolution as that is what determines the sixe of the print - but I see what you are trying to say.

Suvv said:
Therefore if you want a 10"x7" print that printed picture will have 300 pixels in every inch across and in every inch down, i.e. it has a resolution of 300ppi. (3000pixels across divided by 10 inches across, or 2100 pixels down divided by 7 inches down)
Click to expand...

I'd reword slightly.... See red.

Suvv said:
Some PP programs still use the term dpi instead of ppi. This can be confusing because when you print you can also set your printer to spray a certain number of dots per inch (dpi) & this has nothing to do with the ppi/dpi figure in the PP program.
Click to expand...

dpi for some strange reason is used as the standard term these days which is a shame being as it's wrong and when you rightly show the difference below it becomes confusing for the majotrity of people.

Suvv said:
For example I can print a picture at 300ppi, which determines the physical size of the printout and at 600dpi which means that my printer sprays 2 dots for each pixel.
Click to expand...
Click to expand...
 
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Thanks for all the advice I now understand much more!!

One question remains...

Am I to set the print size of each file going to print at its specific ppi to get the size I need?

Or

If I set everything to 300ppi, (say its print size is 7x5) and I send it off to be printed at 18x12, would the printer automatically 'stretch' it and lower the ppi to a good print, or would this lower the quality?

thanks
 
The answer is the printer doesn't stretch the image at all.

You change the image size in Ps to 18" x 12". Easiest way is to use the crop tool.
When you select the crop tool, fil in the width/height numbers along the bar at the top but leave resolutoin blank.

Be aware that 18x12 is a different ratio to a 7x5 so you will need to crop a few more pixels to get that size. Now you have an 18x12 image @ 116.67ppi

That is pretty low and although it may be fine, I'd probably resample a bit to around 150ppi or maybe 180ppi.

Why do you want to print a 7x5 image at 18x12?

When printed the printer will print at 300ppi - At 117ppi though close up you will probably see a reduction in quality as compared to the 7x5 at 300ppi BUT when it's hung oin the wall and you look at it from a few feet you will be unlikely to see any difference.
 
Could someone tell me what the resampling does please? :help:
 
EOS_JD said:
The answer is the printer doesn't stretch the image at all.

You change the image size in Ps to 18" x 12". Easiest way is to use the crop tool.
When you select the crop tool, fil in the width/height numbers along the bar at the top but leave resolutoin blank.

Be aware that 18x12 is a different ratio to a 7x5 so you will need to crop a few more pixels to get that size. Now you have an 18x12 image @ 116.67ppi

That is pretty low and although it may be fine, I'd probably resample a bit to around 150ppi or maybe 180ppi.

Why do you want to print a 7x5 image at 18x12?

When printed the printer will print at 300ppi - At 117ppi though close up you will probably see a reduction in quality as compared to the 7x5 at 300ppi BUT when it's hung oin the wall and you look at it from a few feet you will be unlikely to see any difference.
Click to expand...

Thanks.

I don't want to print a 7x5 to a 18x12. They were just example figures to show what I meant.
 
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