Canon EOS Rebel XT Resolution Help - How do you increase resolution of images?
I have an 8 megapixel Canon EOS Rebel XT. It is a very good camera, but I notice that when I open images in my editing program that the resolution of the images is always 72 pixels. The size of the image is huge - 3456 X 2304 - but how can I increase the resolution? Any tips on getting sharper images would also be appreciated. Thanks.
January 6th, 2009 at 8:11 PM
Image pixels, image size, image quality, and DPI(dots per inch) are a bit confusing.
Firstly, the real thing that should concern you is DPI. This is the actual numer of dots of ink per inch that your printer will allow you to put onto a print. Most computer moniters are designed to resolve 72DPI. The average magazine quality picture (like in Sports Illustrated) is 180DPI. Most color printers default at 300DPI and many will allow you to print into much higher ranges than that. DPI is controlled by your image editing software and your printer settings.
Some suggestions. Always take your original camera pictures at the highest resolution your camera will allow. If your camera allows it (yours does) and your image editing program will will accept this format (Adobe Photoshop, Adobe Lightroom, Adobe Elements, and several other better image editing programs do), shoot in RAW format. Always keep your original camera images in a separate folder and NEVER altar them. Always start working from your original images towards whatever your final goal is, and then save the final result in a different folder (and ideally with a different file name) then your original camera image came from. This practice will allow you to get the best possible result for the use you are trying to achieve.
The image size in pixels is what determines the maximum size you can reasonably expect to print your image.
Resolution refers to how sharp your image actually is. Resolution is the maximum image quality your equipment can produce. The main reason for less than sharp results is camera (or subject) movement during exposure. The second most common reason is improper camera focus. These are both camera handling problems which are user correctable. Understanding your camera and using it properly will correct these issues.
Hope this information helps… good luck with your photography.
January 6th, 2009 at 8:11 PM
Don't worry about it. You will note that the image size is sown as something like 48" x 32". You will not be printing at that size. I wrote an answer to a similar question quite a while ago that you will find helpful. Just ignore any part that is not specifically directed at your question. The bottom line is that it will all work out when you resize the picture to print at a real world size.
The best tip for getting sharper images is to hold the camera still and focus. That's the wise guy tip, but you can think beyond human capabilities in accomplishing this goal. A tripod is (seriously) the best way to get extra sharp images. For the times when that is not convenient, using image stabilized lenses is a good way to go, especially with the fine line of lenses than Canon makes. I'll add my "IS without IS" answer after the resolution answer, if I can post that much!
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You can not control the pixels per inch in your camera, as this is a function of the sensor. I have found the following ppi for SOME cameras by the following manufacturers. I wonder if this specification is available anywhere. I have four camera manuals in front of me and I can't find it in any of them.
NIKON - 300 ppi
CANON - 180 ppi, 240 ppi
PENTAX - 72 ppi
We "discussed" this by way of question and answers a while back and decided that the ppi file produced by the camera really did not have any effect on the capability to produce a good print. If I take a photo with my wife's 6 MP Nikon and view the image on the screen, it will start out as 300 ppi. If it's a full frame image of 3008 pixels x 2000 pixels, the SCREEN image would be pretty big if I viewed it full sized, but it would print 10.0" x 6.6". If you crop a 5×7 out of this, keeping it as full-frame as possible, it becomes 400 dpi.
With my brother's 6 MP Pentax, the image is 2816 px x 2112 px, but it's at 72 ppi. If you print this without cropping, it would be 39" x 29"!!! If you crop a 5×7 out of this, though, it becomes 402 dpi resolution, which is virtually identical for the Nikon 6 MP camera.
With my son's 6 MP Canon Powershot A620, the image is 3072 px x 2304 px, but it's at 180 ppi. If you could possibly print this without cropping, it would be 17.1" x 12.8". If you crop a 5×7 out of this, though, it becomes 439 dpi resolution, which is a bit better than either of the other 6 MP cameras.
In other words, regardless of the sensor's pixel-per-inch output, 6 MP cameras produced the same resolution when it came time to print comparable images. How about a camera with more pixels?
If I take a photo with my 10 MP Nikon D200 and view the image on the screen, it will start out as 300 ppi. If it's a full frame image of 3872 pixels x 2592 pixels, the SCREEN image would be pretty big if I viewed it full sized, but it would print 12.9" x 8.6", if I had the right paper. If you crop a 5×7 out of this, keeping it as full-frame as possible, it becomes 516 dpi, or higher resolution than the 6 MP cameras. We knew that is would work out like this, though, didn't we?
The REAL question is, what difference does this make in the real world? If we agree that 300 dpi is an excellent resolution for prints, as long as you end up with at least 300 ppi after you are done cropping on the screen, you will get an excellent print as far as resolution goes. All four cameras exceed that amount. I usually resize "down" to 300 dpi before printing, because you can't tell the difference above that resolution anyway. Most people would be quite happy with a 200 dpi print, so go ahead and crop a bit. If you get a print resolution too much below 200 dpi, you will start to see digital artifact in the print and it will be objectionable.
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So, if your goal is an excellent print with dots that are small enough that they are no longer distinguishable as individual dots without magnification, you need to print at 300 dpi. You can go down in resolution to 200 dpi and still have satisfcatory results. The resolution of 200 or 300 dpi is NOT a function of the camera beyond the degree that I have discussed above. It is determined by the software you are editting your pictures with and you usually have enough size to work with using any camera at or above 6 MP to get decent pictures.
Working this out is easy once you understand the concept of print resolution. If you want 300 dpi, just do the math.
4" x 6"
4 inches x 300 dots per inch = 1,200 dots
6 inches x 300 dots per inch = 1,800 dots
1,200 dots x 1,800 dots = 2,160,000 dots or 2.2 MP
5" x 7"
5 inches x 300 dots per inch = 1,500 dots
7 inches x 300 dots per inch = 2,100 dots
1,500 dots x 2,100 dots = 3,150,000 dots or 3.2 MP
8" x 10"
8 inches x 300 dots per inch = 2,400 dots
10 inches x 300 dots per inch = 3,000 dots
2,400 dots x 3,000 dots = 7,200,000 dots or 7.2 MP
I will let you substitute 200 for 300 and do the math on these charts to see what the minimum acceptable resolutions for the various sizes would be.
4" x 6" - 960,000
5" x 7" - 1,400,000
8" x 10" - 3,200,00
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"IMAGE STABILIZATION" WITHOUT "IS"
This is what you have to know about image blur if you decide to buy a camera that does not have optical image stabilization.
Image stabilization is the real deal and it DOES help your pictures, but it's not essential. In the case of Canon's, it's about a hundred dollar upgrade in the SD (Elph) series. I'll add my stock answer on "IS" (image stabilization) after I'm done talking about some other things here and you can check it out if you want to.
When it was my turn to buy a "pocket" camera to take with me when I didn't want to drag out the SLR, I chose a Canon SD900. There are times when "IS" might help, but overall, I don't really miss it in this camera. If you have longer zoom lenses, any degree of shaking will be magnified and "IS" will cut down or eliminate the blur caused by that shaking. There are a few tricks and techniques that you can use if your camera doesn't have it.
First of all, like the old days, just make a conscious effort to hold still. Try to use the optical viewfinder so you can hold the camera up to your face and not at arm's length. You can turn off the LCD preview if you do this and it will save batteries anyhow. Take a breath and hold your breath while you gently s-q-u-e-e-z-e the shutter, trying to avoid shaking the camera as you push the button.
In any mode on most point and shoot cameras, you will see a "shake warning" if the shutter speed is going to be slow enough that there is more risk of your shaking. There are a few things you can do in this situation to minimize the potential for a blurred image.
You can always force the camera to use a faster shutter speed by selecting a higher ISO (sensitivity) setting. You have a few options with most cameras to accomplish this. First, in the manual mode, you can simply select a higher ISO when the light is low and you are more likely to have trouble holding still for a longer exposure. This will force a faster shutter speed. In any mode, you can use "AUTO ISO," but you can also use "HI ISO" or whatever your model calls it. This will force the camera to go to the next higher ISO than the normal program would select under the existing lighting conditions. If the normal program would use ISO 100, "HI ISO" will bump it up to ISO 200. By doing this, it will make the shutter speed twice as fast so there is less likelihood of blurring due to camera shake.
Some cameras, such as the Canon SD1000, also have an interesting feature called "Auto ISO Shift" that allows you to make a one-touch adjustment to the ISO if the shake warning icon appears.
The down side of increasing the ISO is that higher ISO settings will introduce a roughness to the image called "digital noise." Until you get up to ISO 800, it's not really much of a concern,
You can also use the flash, which would usually eliminate blur, if the subject is within your flash range.
You can also steady the camera on something or use a tripod and then use the self-timer so the shutter will go by itself without you touching the camera, eliminating the possibility for shaking the camera.
January 6th, 2009 at 8:11 PM
Simple answer: you can't change this tag in-camera. It's meaningless really. What counts are the pixel dimensions, the 3456 x 2304. If it bothers you, you can change it in your editing program, but it doesn't affect the inherent quality of your images. For printing hard copies, you might want to change it, depending upon what program you're using to print. I use Qimage to print, and it takes care of this automatically.
Tips on getting sharper images: 1) use a camera support where you can–a tripod, bracing the camera, a monopod, etc. 2) Use a fast shutter speed to prevent blur. 3) Use a flash to help freeze motion. 4) Use as low an ISO as you can go without getting a slow shutter speed. This will reduce image noise. 5) image stabilization helps, if you've got it. 6) don't use digital zoom. 7) optical zoom increases effects of vibration/camera movement as you get more magnification–adjust your camera steadiness accordingly.