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Old Oct 12, 2004, 12:06 PM   #1
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I have a new 20D. I am not a pro but do have to produce excellent quality 8X10, and some poster - size photos. Sometimes I have to do them enmass. At a homecoming event this last weekend, I had close to 500 photos to PS. My digital Rebel, D30, the family 10D are easy to off load to my card reader for review on and their X and Y resolution show up as 180 unless you are in the raw size. I do not have to interpolate to get excellent prints from these cameras.
Off-loading from the new D20, I was stunned to see the X and Y resolutions come up at 72. I re-read everything, then called Cannon and was told in a very condescending manner, that it doesn't matter what the resolution says, there are more pixels.
I understand that the sensor size is the same as the Rebel, etc., but the pixels ere made smaller so they could say the 20D is putting out 8mp. Reviews seem to feel this may be a handicap as smaller pixels shoved into the same space make for more noise. I do NOT want to have to put every photo into another program to interpolate it up to a 180 resolution. PPI being larger, notwithstanding, a photo from the 72 resolution size, shot at the highest non-raw setting looks like a photo shot at a 72 resoltuion. Not good enough for a print.
In order to get a good print, I had to up-size prior to doing the usualy PS. This makes my work a 2-step process which adds considerably to lengthy photo sessions. No one else seems to be concerned with this which is a very big problem for me. Have I missed something else you all see? Is there no way around this 2-step process?
thanks for any help.
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Old Oct 12, 2004, 1:10 PM   #2
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Isnt JP(E)G allways 72 DPI?

As long as i know the jpeg format cant store DPI informations as most other (mainly lossless as Tiff) do.
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Old Oct 12, 2004, 5:02 PM   #3
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Thedpi flags you see have nothing to do with the resolution of the image. Theseare onlyflags that some editors use for viewing of a photo.

Most cameras actually set them to 72 dpi (which shows you an extremely large image size on screen). As long as you don't check any resample boxes, you can change these flags to anything you want for onscreen viewing, and still maintain the full resolution image for sending to the printer.

The actual resolution you print at will depend on the print size.

For example, if you print an 8x10" print from a 3504 x 2336 resolution image (the 8 Megapixel image size your camera produces), you'd end up with 292 pixels per inch after cropping to 2920 x 2336 for the correct ratio of width to height for an 8x10" print.

When printing, the correct term is actually PPI (Pixels Per Inch) versus DPI (Dots Per Inch), since inkjet printers use multiple dots per inch to represent a single pixel. But, you often see these terms used interchangeably.

2920 pixels / 10 inches= 292 pixels per inch

2336 pixels / 8 inches = 292 pixels per inch


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Old Oct 13, 2004, 12:19 AM   #4
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Thanks for the reply and the explanation, however, I think we are talking about 2 different things together.
The X and Y resolution at 72, pops up on the info for the photo under Photoshop. Under PS, the other cameras I mentioned, come up as 180, unless shooting RAW, which I almost never do. My monitor is a 72 resolution - I don't want to resample artifically with this extra step. Prints from the other Cannon cameras which read at 180 resolutions, print beauts at 8X10 and larger. This 20D, without the extra resampling step, does not. Same lenses. Same set up.
I understand the diff. between ppi and dpi and have not altered the info on the printer. It stays at a standard setting and I use PS 7, without resampling, to print the usual 8X10's that look quite sharp frm the REbel. The information the camera is sending to PS shows this 72 resolution every time I off load from the 20D and it is always 180 from the D10 and the Rebel and the D 30.
I have taken the same photo in the 20D, resampled it, sized it up and changed the resolution--it looks as good as the same photo from both the 10D and the Digital Rebel. I hoped for more.
I can't believe they have wired this baby so I have to resample and size it up with each photo.
I'm very frustrated and distressed I couldn't get Cannon to even understand that I don't shoot RAW, and if I had thought I would have to resize every time I want to do a photo, I would have stayed with the Rebel. I am sorry I 'm not making myself clear, but I really want some help here.
I have done much research and saw another post from someone asking the same thing on another site. They blew the person off with the same junk about - "oh you do'nt know what you are talking about because it has so many more pixels, it's ok." Sounded like the Cannon guy I talked to.
Regardless, from camera to photoshop, with no resizing, the largest available photo, on the Rebel and 20D are not equal. Without resizing and that extra step, the Rebel wins hands down and the 20D is fine IF you resize.
Is this the way it is meant to be used? Resizing each photo? Please try to help me "get it" one more time.
I can get some info wrong, but I know what my eyes see in unresized photo comparisons.
thanks for your patience and help
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Old Oct 13, 2004, 1:44 AM   #5
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omegaman wrote:
Quote:
Thanks for the reply and the explanation, however, I think we are talking about 2 different things together.
The X and Y resolution at 72, pops up on the info for the photo under Photoshop. Under PS, the other cameras I mentioned, come up as 180, unless shooting RAW, which I almost never do. My monitor is a 72 resolution - I don't want to resample artifically with this extra step. Prints from the other Cannon cameras which read at 180 resolutions, print beauts at 8X10 and larger. This 20D, without the extra resampling step, does not. Same lenses. Same set up.
These are only flags in the image header, used by some editors for display purposes.

They are called x andy resolution for the size they'll display the image at (how many dpi to display horizontally and vertically).

The internal layout of the actual image portion of the file is completely independent of the values you are seeing, which are simply 2 fields in the image header to tell the editors what resolution they should be displayed at. Modifying thesevalues does nothing to the image -- whether the camera was putting 300 x 300 in them, or 1 x1 in them.

Now, for display or print purposes, you can change these to whatever you want. But, you don't need to resample the image. You're simply telling the software what size you want to display or print at. That's not changing the internal structure of the image, unless you have resample boxes checked.

Here is an article discussing it:

http://www.photo.co.nz/faq/resolution.htm

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I have taken the same photo in the 20D, resampled it, sized it up and changed the resolution--it looks as good as the same photo from both the 10D and the Digital Rebel. I hoped for more.
I think you are mistaken about what you are actually doing. You should not need to resample the image to a different resolution. Resolution is the heightx width of the image in pixels, and has nothing to do with the dpi values in the header, which is simply instructing the software what pixel density to use for display or print purposes.

Pixels in an image file have no physical size or dimensions. They are simply stored as values (Red, Green, and Blue values for each pixel), with the total number of pixels across and down making up the images resolution.

Again, the X and Y values you see, are simply instructing the software what density to display or print them at. Most cameras actually default this to 72 x 72. Some editors actually let you change these flags independently. However, most only let you set it as one value forDPI (with the x any values changing "behind the scenes" for display or print purposes). Again, this does not modify the actual image.

Quote:
Regardless, from camera to photoshop, with no resizing, the largest available photo, on the Rebel and 20D are not equal. Without resizing and that extra step, the Rebel wins hands down and the 20D is fine IF you resize.
Is this the way it is meant to be used? Resizing each photo? Please try to help me "get it" one more time.
I think you are mistaking changing the dpi boxes to what size you want for printing or viewing with resampling. One has nothing to do with the other.


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Old Oct 13, 2004, 7:33 AM   #6
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Omegaman-

JimC is correct. Read his explanation a couple of times, it is simple but you have to "change gears" in your thinking. It takes a while to have it make sense.
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Old Oct 13, 2004, 10:47 AM   #7
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This is a place where JimC might have used more software than me, but I think he misspoke slightly.

I know of no software (but I haven't used a lot of image editing software) which uses DPI for display purposes. My understanding is that DPI is only used for printing.

I basically agree with everything else JimC said, though.

omegaman, you have a misunderstanding which is effecting your perception of the situation. The 20D produces more data (a larger image) than the 10D. How you tell the printer to print that (what dpi to use... I agree with JimC, though, that ppi is a better term) effects how large a print you want to make. If you tell the printer to use too few pixels per 1 inch of picture it will look bad. If you tell it to use too many pixels per inch it will either not look any better than the "Right amount" for awhile and then it will look bad.

Just as JimC said, you do not have to resample the picture to change the DPI. You can (there is a check box to do so in PS) but you don't have to. I do this quite often. I change the DPI I'm printing at to 180 (some times 200) without resampling and then I use print preview to see how big the print will be. If it's acceptable I print it. If not, THEN I go and resample the image to get the size print I want at the DPI I want (I enlarge the picture in 5% increments as this often produces better results than one large jump... but not always.)

omegaman, this is what I believe is happening to you. The picture appears in PS like this:

20D 72 DPI at 3504 x 2336 = 48.6" x 32.4" (and looks bad but big)
10D 180 DPI at 3072 x 2048 = 17" x 11.4" (and looks good)

But if you just changed the DPI (not resampled) the 20D's picture you'd get:
20D 180 DPI at 3504 x 2336 = 19.5" x 13" (and looks good)

Note that the same number of pixes at a higher DPI produces a smaller picture, but with more data per inch of paper the results should look better. The 20D produces a larger print (by a noticable amount) than the 10D at the same DPI .

Does this help?

BTW, I thought there was a setting in PS that would just relabel a picture to the DPI you requested. It doesn't resample, it just changes the DPI values in the header (as JimC says, the DPI value is just some extra info stored in the header of the picture.) You might want to check what that is set to.... Of course, I could be remembering wrong, but I think I remember seeing that.

Eric
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Old Oct 13, 2004, 1:09 PM   #8
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OK, I am going to re-read these replies 10 times and think and try to re-shape that thinking. I do kindly appreciate your patience and do hope it is wrong-headed thinking over a silly thing that can be quickly amended. I haven't that much money to throw out and be doing another step.
Yes, I was thrown hard for the Photoshop image coming up at 72 while the other cameras show 180 and felt even worse when
I printed a straight print and saw the poor results.
Thanks-I'll be back. You are very kind.

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Old Oct 13, 2004, 1:29 PM   #9
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Eric:
That is very helpful. The inquiry was from my better half. She had a 300D Rebel and wanted the 180 resolution and wondered how she could get that from her 20D without an extra step. Me I cling to my 10D.
RC
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Old Oct 13, 2004, 3:23 PM   #10
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Quote:
Originally Posted by omegaman
Yes, I was thrown hard for the Photoshop image coming up at 72 while the other cameras show 180 and felt even worse when I printed a straight print and saw the poor results.
I'm not surprised you were unhappy with the poor results. at 72 DPI I would expect the results to be bad. My problem is that I really want to crop the picture for better composition and then print at 11x14 or so (with my 10D) and to do that I have to upsample or use a low DPI. If the picture is sharp enough with good detail it can survive the upsampling/interpolation. Other times it can.

Humm... now there is an interesting experiment. Where is the thresh hold (and its probably picture dependent, but maybe there are loose/general rules) where its better to lower the DPI vs. upsampling to get the size print you want.

Oh, its probably printer (and maybe software as well) dependent.

Eric
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