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Old Jul 22, 2004, 5:48 PM   #1
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I have worked in photography field for years now and until now have avoided big bad DIGITAL! Photoshop is the closest i get.

So now I have to learn, 21st century and all that! So I thought you professionals could help with some questions.

I have been looking at Canon Digital Cameras mainly the EOS 300D & EOS 10D mainly because I use the Canon EOS 10 on a average day.

The Image Size for the Canon 10D are as follows;

Image Size :

L/F 3,072 x 2,048 2.4 MB
L/N 3,072 x 2,048 1.2 MB
M/F 2,048 x 1,360 1.3 MB
M/N 2,048 x 1,360 0.7 MB
S/F 1,536 x 1,024 0.8 MB
S/N 1,536 x 1,024 0.4 MB
RAW 3,072 x 2,048 8 MB

So I assume that all these sizes are 72dpi?

If so when I put a photo into photoshop and scale it by 300dpi with constrain proportions I end up with a image that is just under A4. Not that impressive in my opinion.

However, have I got this totally wrong? I do hope so.

DPI to me is very important as I work in print, and need high quality images of 300dpi at A4 and above, maybe this is the wrong option for me? Or there could be a work around I just have not thought about?

Thank for your help and sorry about my ignorance!
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Old Jul 22, 2004, 6:02 PM   #2
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This is a common misconception. The cameras don't take photos at 72dpi by default -- that's just how your software is displaying them (it's a size that most image editing packages have standardized on, even though most monitors use a display resolution that'shigher).

The actual size you see on screen will depend on how the image editing package is displaying them, and the resolution of your monitor. Changing the dpi flag in an image, may alter the way it is displayed in some packages.

For example: A typical photo will be taken at around 2560 x 1920 pixels with most 5MP models (the 6 Megapixel Canon EOS-10Dis actually more than this, at 3072 x 2048 pixels).

So, with a typical 5MP Digicam, if you are displaying an image with software, at 72dpi, you get a very large image size on screen (2560/72ppi = 35.555 inches, 1920/72 ppi = 26.666 inches). So, on an older model monitor (as the 72dpi display standard was supposedly based on), a 2560x1920 pixel image would appear to be around 36 x 26 inches large (with monitor size/resolution entering the equation, too).

But, when you send this same image to a printer, the pixels per inch sent, depend on the print size.

For example: if you wanted the "perfect" 300 pixel per inch print , a 2560 x 1920 image would translate to an 8.53" x 6.4" print (2560 pixels/300 = 8.53, 1920 pixels/300 = 6.4).

The Canon EOS-10D uses a slightly large image sizeof 3072 x 2048. So, at 300 pixels per inch, this translates to a print size of 10.24" x 6.8".

However, most users won't see any difference between 200ppi and 300ppi (unless you look at the photo under magnification).

The printer driver should use all of the resolution (as long as you don't have any resize/resample boxes checked).

Actually, what it's really doing, is taking the image you send it, then converting it again, into the actual DPI printed by the printer model. It knows nothing about what your software is displaying it at -- only the actual resolution of the image in pixels (around 2560 x 1920, in the case of many 5MP models).

If you are using a 3rd party printing service, ask them how many Pixels Per Inch (minimum) is needed for the desired print sizes (most don't even care, with the printer software automatically interpolating -- but for very large print sizes, this can be a problem with some printer types).

As far as print sizes, many will argue that 150 pixels per inch is plenty of resolution, with anything more a waste, since the human eye won't be able to tell the difference at normal viewing distances.

Others will argue that 200, or even 300 pixels per inch is necessary for the best quality. Again, I've found 200PPI to be plenty.

Here's a chart that may help.

http://www.cordcamera.com/products/digital/aspect_ratios.html

IMO, anything above about 180PPI is fine for prints up to 8x10", and even less is can be used for larger prints (because you'll be viewing them from further away). The printer used can make a difference, too -- as many ink jet printers "optimize" the input they receive for photos. Dye Sub printers may require more pixels (300 ppi is best for some dye sub printers).

Here's another chart that takes popular digital camera image sizes, and shows how many pixels per inch you'll be sending to the printer driver for popular print sizes:

http://home.earthlink.net/~terryleedawson/dcnotes/tables.htm#ppi

Also, you can interpolate an image using software (you shouldn't need to, unless you are printing VERY LARGE prints). This does not increase the detail captured originally, but it does add pixels (based on the value of adjacent pixels). This lets you print larger images without pixelaton.

A good free package is irfanview. It has a very sophisticated Lanczos Filter based interpolation algorithm (you'll find this option under the resize/resample menu option). You can download the software (free) from this link:

http://www.irfanview.com

Also, you may want to be aware that some print sizes can result in cropping of your digital image. Refer to this chart, to determine the percentage of your image that will be used, at popular digital camera sizes, for standard prints:

http://home.earthlink.net/~terryleedawson/dcnotes/tables.htm#frameutil

Some printing services (like Photoaccess.com) offer "digital size" prints (no cropping of your photos). Others don't. So, you may want to crop your photos for the print size you'll want. But, don't mess around with DPI count (or check any resize/resample option boxes). More resolution than needed is fine to send to a printer.

Now, there is a flag for dpi in the image header, but Changing it is only changing a byte in the image header and doesn't really change the image at all (other than how it may be displayed in some image editors). This has NOTHING to do with the pixels per inch you are printing at.

But, I'd advise to never try and change this setting with Image Editing Software, as some software may try to resize an image based on this flag. Printing software ignores it.

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Old Jul 22, 2004, 6:14 PM   #3
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If you REALLY need the extra detail for much larger prints, there are other options. Digital SLR Cameras are available in resolutions of 8, 11, and 14 Megapixels from some manufacturers now. You can also get even higher resolution "Digital Backs" for Medium Format Cameras.

However, the prices of these models increases substantially over a model like the EOS-10D you are looking at.

I think you'll find that the actual detail captured by a camera like the EOS-10D will rival 35mm Film SLR's, and you can interpolate the image if larger sizes are needed (up to a point). Do keep in mind that it takes 4 times the resolution to capture the same detail in pixels per inch, each time you double the print size. This is because resolution is composed of width x height.

Added:

Here are some articles you may find of interest:

Canon EOS-D30 (3 Megapixels) compared to film:

http://www.luminous-landscape.com/re..._vs_film.shtml

Canon EOS-D60 (6 Megapixels) compared to medium format:

http://www.luminous-landscape.com/re.../d60/d60.shtml

Canon EOS-1Ds (11 Megapixels)- includes comparisons to medium format:

http://www.luminous-landscape.com/re...ds-field.shtml

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Old Jul 22, 2004, 9:08 PM   #4
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grant.smith wrote:
Quote:
... DPI to me is very important as I work in print, and need high quality images of 300dpi at A4 and above, maybe this is the wrong option for me? ...
Keep in mind that DPI has no meaning whatsoever until you print - for the camera and editing software DPI is just a number stored with the image's EXIF data. Image quality (noise, focus, exposure, ...), subject matter (foggy lakeshore, butterfly wing, ...) will be as important as total pixel count in determining how large a print you can make. The combination of DPI and the pixel count (horiz and vertical) will determine how large the print will be, but not how good it will be.
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Old Jul 22, 2004, 11:33 PM   #5
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As Bill stated, DPI is only for printing. Cameras use Pixels instead of Points.

The numbers, 3072x2048, and so on, are the number of rows and columns of light capturing sensors on the camera's chip. If you multiply 3072 * 2048, that is where they get the 6.3 MegaPixel figure.

Looks like Jim has given you some great articles to read about digi cams.

You will also notice with digi cams that there is a lens factor. I think the Canon 10D is 1.6 * the focal length of the lens. So a 200mm lens would actually be 320mm. This is great if you need a telephoto, but not so great if you need a wide angle.


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Old Jul 22, 2004, 11:42 PM   #6
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I have printed 11x14's using my 10D and I am very happy with the results. I upsampled the images to the DPI I was told to use (250 for one shop, 320 in another) and the did some post processing (selective sharpening, halo reduction.)

I was told by someone better at photoshop and printing that the same file that I used for the 11x14 could have been upsampled again and be printed at 13x18 (13x19?). I never saw that but he does know what he's doing, so I believe him.

As other have said DPI has nothing to do with anything until you print. Then it's all about what DPI your printer works best at and if you can get the pictures to something close enough that the printer's print engine doesn't mess it up.

I want to take slight issue with something that JimC said:
Quote:
Originally Posted by JimC
As far as print sizes, many will argue that 150 pixels per inch is plenty of resolution, with anything more a waste, since the human eye won't be able to tell the difference at normal viewing distances.

Others will argue that 200, or even 300 pixels per inch is necessary for the best quality. Again, I've found 200PPI to be plenty.
Well, he doesn't really say it, he's quoting others. But I feel that it totally depends on what your pictures are of. Some things don't have as much detail and won't loose impact if upscaled and printed (An ocean sunset, for example.) On the other hand, a highly detailed forest scene with lots of rough bark, great ferns, and the sun shining through the pollen. Now that has detail, and will probably look worse if you tried to enlarge it without taking proper care.

Eric
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Old Jul 23, 2004, 12:17 AM   #7
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eric s wrote:
Quote:
I want to take slight issue with something that JimC said:
JimC wrote:
Quote:
As far as print sizes, many will argue that 150 pixels per inch is plenty of resolution, with anything more a waste, since the human eye won't be able to tell the difference at normal viewing distances.

Others will argue that 200, or even 300 pixels per inch is necessary for the best quality. Again, I've found 200PPI to be plenty.
Well, he doesn't really say it, he's quoting others. But I feel that it totally depends on what your pictures are of. Some things don't have as much detail and won't loose impact if upscaled and printed (An ocean sunset, for example.) On the other hand, a highly detailed forest scene with lots of rough bark, great ferns, and the sun shining through the pollen. Now that has detail, and will probably look worse if you tried to enlarge it without taking proper care.
Eric, I'm confused....This example was not discussing upsampling. It was discussing pixels per inch resolution (as captured by the camera). Yes, I mentioned what other people would argue, so that was quoting them (and my post said that this was what manywould argue, not what I would argue). However, from personal experience, I can see a marked improvement in qualty going from approx.150PPI to approx. 200PPI. After that, I can't see any further improvement with a higher resolution image, which is why I said that I've found 200PPI to be plenty.

For example, if I take an image from a 2MP model and print it at 8x10", then take the same type of photo from a 3MP model and print it at 8X10", I see a marked improvement. However, if I take the same type of photo with a 5MP camera and print it at 8x10", I don't see any further improvement over the 3MP image.

As far as interpolating an image, I agree. Perhaps I need to be clearer in my posts and mention subject type in all of them discussing print sizes..Subject type can make a difference, as I pointed out in this thread:

http://www.stevesforums.com/forums/v...amp;forum_id=9


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Old Jul 23, 2004, 4:36 AM   #8
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Thank you everyone who has replied to my message. Unfortunately I think I'm more confused than when I started! This is obviously going to be a much stepper learning curve than I first anticipated.

So in conclusion, from what I can gather is that, and please correct me if I'm wrong;

Megapixels is actually the area it will cover?;
Everthing I have learnt in print over the years does not apply to digital photography?!;
Photoshop (my preferred picture image package), does not give me a true representation of image size?;
Basically if it covers the area of print, for example A4 it is good enough to be reproduced through a Litho or Digital print process?

Again thanks for your help
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Old Jul 23, 2004, 7:15 AM   #9
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Well...you can make it simple or complex.

Frankly, this is what I do. I do not worry aboutdpi because I have found the largest size I ever have printed was 8 1/2 x 11 border to border. I can't tell with my eyes the difference of the standarddpi of 180, or anything higher for these print sizes. Maybe this is different if your planing on printing larger formats.

I have found that for that size, any camera that is 3 megapixels and up, will get you a fantastic print without having to resample, or play around with the dpi. It does depend upon the printer you use, for it will have a large impact on what your final print will look like.

Besides, if you want to up thedpi of an image, you can easily do so, meanwhile keeping the resolution intact, or you can do so, while resampling it to a smaller or larger size.l

Now, digital cameras have several resolution settings as you have stated in your first post. I always shoot at the highest setting. I do so thinking that I can always downsample an image to fit my needs, as opposed to upsampling one. This pixel resolution translates into the viewing size on your monitor. Thus, if your resolution is larger then your monitor resolution settings, then you can scroll around looking at your photo. Likewise, all digital darkroom programs give you the option to view the photo at your screen resolution to see your whole picture.

Thus, I would not be so concerned about proper resolution. Chances are, you are going to experiment to find out what works best for you. You may find that for your applications, you may never have to play with thedpi settings (small prints up to letter size). If you find this is not good enough, then you can up your dpi and photo resolution to your liking.




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Old Jul 23, 2004, 8:50 AM   #10
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grant.smith wrote:
Quote:
Thank you everyone who has replied to my message. Unfortunately I think I'm more confused than when I started! This is obviously going to be a much stepper learning curve than I first anticipated.
Well, my "long winded" response may have been confusing. Perhaps I should have kept it simpler. My apologies.

Quote:
Megapixels is actually the area it will cover?
Pixel stands for "Picture Element". One Million Picture Elements (Pixels) is commonly called1 Megapixel.2 Million Pixels iscalled2 Megapixels, etc. A Pixel is the smallest portion of an image that can be displayed or printed.

When discussing the sensors in a digital camera,each pixel is captured by a photosite (basically, a photosensitive diode, or photodiode). After some complex processes internal to the camera, the values for colorand brightnessare represented digitally in an image file for each individual pixel element.

This is an oversimplification, since most image sensors are actuallymonochrome, so you have color filter arrays in most sensor types, designed so that some photosites (the individual photodiodes in the sensor) aremore sensitive tosome colors, versus others. However, I wouldn't worry about needing to understand this part.

Take the sensor in the Canon EOS-10D you are considering as an example. It's sensor is producing a file representing 3,072 x 2,048 pixels (6,291,456 pixels or picture elements). So,this referred is referred toas 6.2 Million Pixels -- or more often than not, rounded to 6 Megapixels.

Basically, think of the sensor in a Digital Camera as a rectangular wafer, containing rows and columns of photosensitive areas (the photosites for the individual pixels).When you see the dimensions of an image represented, it's referring to the number of rows across, and the number of columns down. When you multiply rows by columns, you determine the total resolution of the sensor in pixels.

Quote:
Everthing I have learnt in print over the years does not apply to digital photography?!;
Sure it does. My first camera was a Canon Rangefinder, given to me by my father, that had no autoexposure, etc. I used a separte light meter with it to help with exposure. What I learnedby usingthat camera, still applies to photography. Since then, I've used numerous film cameras, and I'm now on my 7th Digital Camera. Only the medium has changed. Now, instead of film, you have a sophisticated electronic sensor in it's place.

You will need to make some adjustments with Digital. For example, you will need to make allowances for focal length differences when using a camera with a sensor that is physically smaller than 35mm film. With the EOS-10D, a lens with a focal length of 50mm, will behave like a lens with an 80mm focal length. This is because the image circle from a lens designed for a 35mm camera is larger than the sensor. So, you have to multiply the actual focal length of the lens by 1.6 to get the equivalent focal length when used on this model. This is known as a "Focal Length Multiplier", or more accurately, the "Crop Factor".

In aDigital Camera with a "full frame" sensor (like the EOS-1Ds), the sensor is the same physical size as 35mm film, so no focal length adjustment is needed.

Quote:
Photoshop (my preferred picture image package), does not give me a true representation of image size?;
Photoshop has no way of knowing what the size of your monitor is. The display standards for most image editing packages were developed many years ago, based on very low resolution monitors. For whatever reason, a 72dpi standard was adopted by many of these packages. So, when you tell someimage editors to display a photo at 300 dpi on a lower resolution monitor that is 14 inches diagonally, it will appear to be much larger, than it would be on a larger 19 inch monitor set to a higher display resolution.

So, the answer is no. It is not giving you an accurate representation of true image size. It can't tell your monitor size.

Quote:
Basically if it covers the area of print, for example A4 it is good enough to be reproduced through a Litho or Digital print process?

Again, don't go by what you see on screen, it's not a true representation.

If I may make a suggestion, download a couple ofsample images from reviews, with a couple of different subject types, then print them so you'll see what to expect.

I've printed many an 8x10" photo over the years from digital cameras, including from 2 Megapixel Models like my older Nikon Coolpix 950, thatfriends have been stunned with the quality from. Now, if I take8x10" photos printed with a similiar camera model -- for example,a Coolpix 990, which is a 3 Megapixel model I once owned, then compare them to similiar photos taken with the 2 Megapixel Model, you can see an noticeable increase in detail captured. However, if I compare these photos to 8x10" prints of similiar subjects from my latest 5 Megapixel Camera, I see no further improvement in detail captured, at this print size.

Why not? Because at this print size, my eyes are unable to distinquish the extra detail the image sensor is actually capturing.

Now, you will need to make sure you have sufficient pixel density for the print size you want. Otherwise, the image will "pixelate". This is when you begin to see the individual pixels in an image. With some printer types, this density is more important, compared to other printer types.

As mentioned earlier, you can interpolate an image to increase pixel density to allow larger prints, to prevent this from occuring. This will prevent the pixelation, but will not increase the actual detail captured by the sensor. However, I think you'll find that the actual detail captured by the sensor by a camera like the EOS-10D you are considering, will be as good as most 35mm film. Actually, you'll probably find it better, because larger prints from 35mm film are limited by grain -- especially if youuse higher ISO Film. The images fromthe sensor in the EOS-10D will be much cleaner. Read the articles I mentioned in my original post for some comparisons.

Also, try downloadng some test images,have them printed, and let your own eyes be the judge.

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