Resolution question

[DAG123]

I am very new to photography. I got a Canon EOS 350XT D for Christmas. I was hoping to get some insight on how to make a photo like this brighter. The white in the hood fringe is really very white. This was a snow day. Some questions:


1. This photo was taken at 3456 x 2304 but the resolution is only 72 dpi...I don't understand that, will this affect the quality when I get it developed?

2. Settings were F5, 1/60 shutter, 44mm focal length and ISO 100.

3. What does the term focal length refer to?
4. There is a blurry snowflake falling across her hat, how would I make that in focus...or is that impossible?


Thanks in advance

http://www.salmo.net/picture.htm

[Hellashot]

The only comment I'll make is you should have used a fill flash to brighten up her face when you took the picture.

[Scottes]

1) DPI means nothing until it's time to print. Ignore it for now. When you go to print set the DPI to 300. It will not change anything at all in the picture, it just tells the printer the final size. (Which would make this about an 11.5 x 8.3 picture, so it will probably need to be cropped to 8x10.

2) OK.

3) The length of the lens. Looks like you had zoomed to put the lens at a 44mm length.

4) Pretty much impossible. At least it's so difficult that it's not worth the bother. It's not distracting in my opinion.

Overall the image is good, but could use a little brightening. A flash would have helped when you took the picture, but it's not so bad - a little editing would make this work out well. What image editing package do you use? Photoshop or Elements? If so, pop up Levels and move the middle slider a little to brighten it. It doesn't need much.

[SkipD]

4. There is a blurry snowflake falling across her hat, how would I make that in focus...or is that impossible?The snowflake is not out of focus. It moved during the time the shutter was open, and you're seeing a streak because of that.

If you don't like the snowflake, you can "clone" it out in Photoshop (or other editing software), overlaying other parts of the hat to look like the snowflake isn't there.

[Citizensmith]

DPI affects how large a photo will print, not directly the quality of the image. Your photos are 3456 x 2304 dots across. At 72DPI they would print out at 48x32 inches. Hope you have a big printer. At 300DPI they would print out at 11.5x8 inches. Still pretty big. If your target was a nice 10x8 to hang on the wall you should stick with the 300DPI and then crop and resize the image down to 3000x2400 (resize to 3600x2400 then decide what to crop of the sides).

[DAG123]

Thanks all...

Still confused on the term 'focal length'
Is that the actual physical length of the lens? Sorry for not grasping this.

[Citizensmith]

Its the distance from the focal point of the lens to the image plane (sensor).

It is slightly abstract as a given focal length will have a different appearance depending on the image size. Generally though, for film or full frame digital cameras, 28mm and shorter is wide, 85mm and longer is telephoto, and everything in the middle is normal. For a camera like the XT which has what is refered to as the APS-C size sensor the focal length on the lens (for instance 18-55mm) is multiplied by a 1.6x "crop factor" to give a film equivalent of 28-90mm.

Hopefully that actually explained things rather than increasing confusion. :)

[Jon]

Thanks all...

Still confused on the term 'focal length'
Is that the actual physical length of the lens? Sorry for not grasping this.
It's the distance (simple case - single element lens, like a magnifying glass) from the lens at which an image of an infinitely-distant object will form. For multi-element lenses like in our cameras, there's the notion of front and rear nodal points, which behave as the center of a simple lens would.

[DAG123]

Got it...

Thanks

[Robert_Lay]

DPI affects how large a photo will print, not directly the quality of the image. Your photos are 3456 x 2304 dots across. At 72DPI they would print out at 48x32 inches. Hope you have a big printer. At 300DPI they would print out at 11.5x8 inches. Still pretty big. If your target was a nice 10x8 to hang on the wall you should stick with the 300DPI and then crop and resize the image down to 3000x2400 (resize to 3600x2400 then decide what to crop of the sides).

Have you ever gone into PSCS or PSCS2 and used "File->Print with Preview" ?

You will notice that after choosing Landscape or Portrait in Page setup, that you can then offset from a corner or center on the page.

Printing size is determined only by using the scaling feature. No dpi settings!

[Robert_Lay]

Thanks all...

Still confused on the term 'focal length'
Is that the actual physical length of the lens? Sorry for not grasping this.

The focal length of any lens, fixed or zoom, is the distance from the lens' optical center to the image plane when the lens is focused on infinity. It is normally expressed in millimeters, but is also given in inches on very old lenses.

However, that is usually of no interest in day to day photograpy. What is usually of more interest is the magnification that one lens provides in relation to another. Generally speaking, two lenses of focal lengths f1 and f2 will provide an image from lens 2 in relation to the size of the image from lens 1 that is f2/f1 times as big.

Numeric example:
An 85 mm lens and a 50 mm lens - the image from the 85 mm lens will be 85/50 = 1.7 times as big as the image from the 50 mm lens.

[Citizensmith]

Printing size is determined only by using the scaling feature. No dpi settings!

And just what exactly do you think PS is doing when it scales. :)

[edistoimaging]

In Photoshop, you could use Levels, then use the eyedropper tool on the far right to set a white point. Experiment with different white shades until you get effect you want.

[Robert_Lay]

And just what exactly do you think PS is doing when it scales. :)

I'm afraid to ask ;)

[Robert_Lay]

And just what exactly do you think PS is doing when it scales. :)

That's such an interesting question that it deserves a better answer. I got to thinking about it when I was doing some printing today and was comparing use of File->Print against File->Print with Preview.

Again, I asked myself just what is it doing in Print with Preview when you set the print size to some physical dimensions?

I think you have an idea of what you think it's doing, but did not say.
I have now made up my mind about what it is and is not doing, but I don't know of any way to find out for sure. I'm convinced that it does not resample. That leaves us with "scaling" as meaning that it simply adjusts the dpi to agree with your requested physical dimensions.

Would you like to share your thoughts on that?

[Citizensmith]

Sorry, missed the previous post.

As far as I'm aware it does exactly what you said, which is why I was trying to make the point that there isn't too much difference between manually adjusting dpi and just printing it and getting PS to make it fit.

I did mention resizing as part of cropping to achieve the correct aspect ratio for your desired print format. Not necessarily the best way, just the way I always do it.

I can think of one issue that could change which works best. Are printers better at certain DPI. For instance my printer is listed as being able to do up to 9600dpi. Is it better at a distinct division of this (say 600dpi) as opposed to a photoshop assigned to get the best fit version (say 574dpi). I've no clue.

[Robert_Lay]

Sorry, missed the previous post.

As far as I'm aware it does exactly what you said, which is why I was trying to make the point that there isn't too much difference between manually adjusting dpi and just printing it and getting PS to make it fit.

I did mention resizing as part of cropping to achieve the correct aspect ratio for your desired print format. Not necessarily the best way, just the way I always do it.

I can think of one issue that could change which works best. Are printers better at certain DPI. For instance my printer is listed as being able to do up to 9600dpi. Is it better at a distinct division of this (say 600dpi) as opposed to a photoshop assigned to get the best fit version (say 574dpi). I've no clue.

In the book, "Photoshop CS Artistry", by Haynes and Crumpler, they have an exhaustive chapter on this issue. I don't know that I believe everything they say, but if you have access to the book, see pages 187 and 188.

Basically what they say is that if you have one of the Epson Stylist Photo Printers with printed dpi's of 720 to 2880, that you should use an image file with about 360 ppi or higher. He bases that on the fact that those Epson printers use the dots a bit differently than do the dye subs or a LightJet 5000.

He also says that when your destination is publishing as a half-tone, the file should have a ppi of twice the line screen frequency. That makes sense with respect to the Nyquist sampling criteria, I guess.

[Bodog]

Sorry, missed the previous post.
I can think of one issue that could change which works best. Are printers better at certain DPI. For instance my printer is listed as being able to do up to 9600dpi. Is it better at a distinct division of this (say 600dpi) as opposed to a photoshop assigned to get the best fit version (say 574dpi). I've no clue.
That's a question for which I would like to see an explainable answer. I've always just sent all my pixels to the printer and let the printer adjust the pixel size on the fly, based on the chosen print size. But I've seen several sources that indicate that printers have a "native" size that produces better prints. I use an Epson 2200. Some posters here have stated they heard that Epsons prefer a 240 ppi file. I recently read a newsletter from another source that stated the Pro Epsons need a 360 ppi file, while the desktops need a 720 ppi file, but even divisibles (180, 270, 360) are OK. It seems to me that any gain in perceived print resolution would be lost in re-sampling the image to the native resolution of the printer. Lately I've been Using only 180 and 360 PPI files for printing, to see if I could see a difference, and frankly I can't. I'd appreciate hearing from anyone who can explain why one size is better than another for a given printer in terms I can understand.

[Robert_Lay]

That's a question for which I would like to see an explainable answer. I've always just sent all my pixels to the printer and let the printer adjust the pixel size on the fly, based on the chosen print size. But I've seen several sources that indicate that printers have a "native" size that produces better prints. I use an Epson 2200. Some posters here have stated they heard that Epsons prefer a 240 ppi file. I recently read a newsletter from another source that stated the Pro Epsons need a 360 ppi file, while the desktops need a 720 ppi file, but even divisibles (180, 270, 360) are OK. It seems to me that any gain in perceived print resolution would be lost in re-sampling the image to the native resolution of the printer. Lately I've been Using only 180 and 360 PPI files for printing, to see if I could see a difference, and frankly I can't. I'd appreciate hearing from anyone who can explain why one size is better than another for a given printer in terms I can understand.

Dear Bodog,

I'm with you 100%, in principle, when it comes to sending all the pixels to the printer and none to the bit-bucket. You probably noted my disclaimer about not necessarily believing everything that Haynes and Crumpler say in their book.

If I am printing to an attached printer and using File->Print instead of File->Print with Preview, then I take the view that the dpi is irrelevant, leave the pixels alone and do a change of the physical dimension in Image->Image Size with resampling not enabled. You have to set the physical dimensions to the desired print size, otherwise it would print exactly as big as the current setting,

It's another story if using File->Print with Preview, because there you can't change the pixels and you can't explicitly change the DPI - all you can change is the physical dimensions, which is what you have to do to get it to print at your desired size.
We have no idea what File->Print with Preview does in secret, but it seems to give good results.

Is all of that consistent with your experience?

[Bodog]

Pretty much so. I always use print with preview, so I can't comment on printing directly, but assume the image would be printed full size that way. I normally would not change the ppi in Image> Image size, but have done it on occasion. Like you I would set the size in Print preview an let the PPI take care of itself. (BTW, that's also a quick way to crop without altering the image.) Never had a problem with visible pixelization, etc. But then I don't loupe my prints either. I have a couple of the earlier Photoshop Artistry books. I'll see what they say. I'll be interested in seeing some others' comment on this issue...

[Carzee]

I'm trying to get my head around this.

To date I have learnt (in regard to my Epson R800) to use image resize in PS to make a pic fit best to an A4 paper. The starting point is that A4 is 297 x 210. To make a pic fit I'll resize the pixels down to 3300 x 2200. ( for a typical 20D 8mp image - needs a bit of shrinking to those dimensions mentioned - a 10D 6mp image will need upsizing).

Gives quality as far as I can see. Should I make the res to 360 dpi.

[tzalman]

I'm trying to get my head around this.

To date I have learnt (in regard to my Epson R800) to use image resize in PS to make a pic fit best to an A4 paper. The starting point is that A4 is 297 x 210. To make a pic fit I'll resize the pixels down to 3300 x 2200. ( for a typical 20D 8mp image - needs a bit of shrinking to those dimensions mentioned - a 10D 6mp image will need upsizing).

Gives quality as far as I can see. Should I make the res to 360 dpi.

I'm afraid I don't understand why you do that. Why did you choose those numbers? 3300x2200 retains the proportions of the original image, 1.5. An A4 page is 1.41428. All you've done is throw away pixels and gone from 283 dpi to 266 dpi (assuming a borderless A4). Or 312 to 294 with a 1 cm. margin. Where's the advantage in that?
Elie

[SkipD]

I'm trying to get my head around this.

To date I have learnt (in regard to my Epson R800) to use image resize in PS to make a pic fit best to an A4 paper. The starting point is that A4 is 297 x 210. To make a pic fit I'll resize the pixels down to 3300 x 2200. ( for a typical 20D 8mp image - needs a bit of shrinking to those dimensions mentioned - a 10D 6mp image will need upsizing).

Gives quality as far as I can see. Should I make the res to 360 dpi.Forget setting the "resolution". There's no reason whatsoever to define the resolution for making normal prints. You want the maximum resolution available in the image file. If you start defining resolution, then the software has to change the image - which could cause problems with the image.

Just crop to the ratio of the final print without entering anything in the "resolution" field. In other words, put numbers into the width and height fields, but leave the resolution field empty. Then tell the software what paper size to print to. You'll get the maximum possible resolution for the image.

[Robert_Lay]

Dear tzalman and SkipD,
I am becoming convinced that the single most important deficiency in the understanding of digital imaging is the concept of the virtual image (which has no physical dimensions - only a width and height in pixels) and the distinction between that and the simple inverse proportionality relationship between dpi and physical size.

I keep agonizing over a model that would be easy for people to grasp and would allow people to more quickly visualize how the virtual image (the data file) is so fundamentally different from the rendered image.

[tzalman]

Bob -
I see three major culprits:
1. The camera manufacturers. If they would just delete that stupid dpi line from the Exif life would be so much simpler.
2. Print labs and publishers that demand a certain dpi without explaining that dpi is relative to print size.
3. PS, which in its attempt to serve everbody from snapshooter to graphic artist creates much confusion.
Elie

[Citizensmith]

Just crop to the ratio of the final print without entering anything in the "resolution" field. In other words, put numbers into the width and height fields, but leave the resolution field empty. Then tell the software what paper size to print to. You'll get the maximum possible resolution for the image.

Am I missing something here. If you try (in PSCS) and leave the resolution field blank it gives an error message. If you leave it at the default setting (72dpi in Elements, 180dpi in PSCS, funny) and just change the width/height of the image you are going to be resizing the image.

I always try and leave the image as close to its original pixel size as possible and change the resolution as necessary to get it to the width/height I need. This sounds like the exact opposite of what you do.

[SkipD]

Am I missing something here. If you try (in PSCS) and leave the resolution field blank it gives an error message. If you leave it at the default setting (72dpi in Elements, 180dpi in PSCS, funny) and just change the width/height of the image you are going to be resizing the image.

I always try and leave the image as close to its original pixel size as possible and change the resolution as necessary to get it to the width/height I need. This sounds like the exact opposite of what you do.When using the crop tool in PS CS2 (and I believe it was the same in PS7), I never put a value into the resolution field. It works every time. All that I do is cut off the portions of the image that I don't want without defining a resolution and without causing the program to resize (change the pixel count of) the image.

[Citizensmith]

OK now I see what you are talking about, the crop tool. I tend to do cropping using the image resize/canvas resize menus and that was why what you were saying didn't make sense.