Resolution - will I ever understand this?

Nordic

Hi!

I recorded a little Photoshop action today that was supposed to write my name in the lower right corner of some pictures. I tested it ok on one of them, then let it run over 20 or 30 pictures.

The writing came out correct on some, and it was huge on others. After searching for half an hour or so, I discovered that the pics where it had the right size had an resolution of 72 dpi. They were right out of the camera. (RebelXT).
The other pics had an resolution of 300. They were shot in RAW, and it seems the RAW converter set the resolution to 300 for printing.

Soooo, is this the same as "upsampling" the resolution in Photoshop?
Is this a bad thing to do?
Does this mean the pics right out of the camera will have a terrible low resolution when printed in a lab? Or that they will upsample it automatically?
Does this degrade the quality of the images?
Should I edit my script to set the resolution to 72dpi for web display?
And store them in 300dpi?
Will I ever understand any of this?
:dunno

Thanks a lot for your help!!!

Regards,
Andreas

StevenV

for web display, what matters is how many pixels high & wide the image is. a 100x100 pixel image will be just over a square inch (or so) on my display, no matter what "resolution" it's tagged to be (72dpi, 96dpi, 300dpi -doesn't matter). My display puts 96 dots in each inch. Period.

from what I understand, the same applies to some (most?) printers, though the resulting image will be smaller because it's printing resolution is higher. So a 300x300 pixel image would print at 1square inch, again regardless of what the "dpi" was set to.

there are, perhaps, some devices which try to use the setting - perhaps someone else knows better than I.

When I'm in PS and cropping, I crop to 8 in x 10 in x 300dpi knowing that will give me 2400x3000 pixels, and that's what my printer uses to actually print an 8x10" picture. I could also crop to 16inx20inx150dpi and get the same effect.

or I could be all wrong, but that's the way it works for me

Nordic

So, what would be better?

1) To keep developing RAW files with 300 dpi, and then downsample for web display?

2) To set the RAW converter to 72 dpi, and then upsample those images I want to print?

3) To keep everything at 72 dpi and stop filling this forum with my resolution questions, and reliying on the lab to upsample the files automatically as they need it for their printers?

Is there a difference if I upsample an image in Phase One or in Photoshop?

Thanks a lot!!

Regards,
Andreas

jfriend

Ignore the dpi completely

Nordic wrote:

So, what would be better?

1) To keep developing RAW files with 300 dpi, and then downsample for web display?

2) To set the RAW converter to 72 dpi, and then upsample those images I want to print?

3) To keep everything at 72 dpi and stop filling this forum with my resolution questions, and reliying on the lab to upsample the files automatically as they need it for their printers?

Is there a difference if I upsample an image in Phase One or in Photoshop?

Thanks a lot!!

Regards,
Andreas

Ignore the dpi resolution - I never, ever do anything with it.

It's a made-up, artificial number that has absolutely nothing to do with the quality of your image. All it's ever used for is "hint" for how large to display your image on some output devices when no other size information is specified. It's not used for web display at all since those images are either displayed at 100% (one pixel in the image for one pixel on the display, dpi not used) or a specific image size is specified and it's scaled to that size (again dpi not used).

I never use it when printing because I always tell my print program how large to make my image on the page and it scales the image automatically to that size, ignoring the dpi resolution setting.

Ignore it.

StevenV

Nordic wrote:

So, what would be better?

1) To keep developing RAW files with 300 dpi, and then downsample for web display?

I'd say "keep developing at full size" - whatever the total number of pixels the camera gives you - and then downsample (i.e. crop to the right number of pixels for the right physical size you want) for the web.

Here's what I mean by that. I've got a 2400x3000 pixel image that I want to use as a thumbnail in a forum post or elsewhere on a website. If I just put use the image as-is, I'd rightfully get slapped with a wet fish - it's just too big. so I can "resample" it down to a lower resolution or I can crop it or both.

Here I use Photoshop's crop tool set to 3 in x 2.3 in @ 72dpi, because I know it'll be viewed on computer displays and I want it to be a reasonable size (yea, I know it'll be a little small for people who run at 96dpi). Here it's just math, I know that the image's 2400x3000 pixels would be too much. cropping to 3x2.3"@300dpi would still give us 900x690 which is still too large for this screen. So in combination with cropping to a different aspect ratio I'm having it "resample" to 72dpi - throwing away a lot of the image - to get it to a more reasonable size for a "thumbnail". 3x2.3@72dpi = 216x165:



short version: edit away with all the pixels you've got, then resample to what the output device is (if you need to).


Oh, and when you start dropping text on top of it (which is where your post started), as long as you're consistant then you should be ok.

Nordic

Thanks a lot guys!!! It slowly starts to make sense!

Regards,
Andreas