BetterPhoto Q&A
Category: New Answers

Image Size for Rebel XT

I have been playing with my new camera and have noticed a few things with image size etc that I haven't been able to work out.

Ok, I took a few pics on the weekend at highest quality setting. Down loaded them on the computer. When I went into Adobe I checked the image size out and it said something like 35inch (I can't remember exactly) but it said 72dpi. WHich I know is not print resolution. So I changed the resolution up to 300dpi (print res)and it obviously changed the size of the print down (to about 8x6 I think). So, I've been told I can print an A2 size no problems. So how do I do that without loosing any unnecessary image quality? I am really a little stuck on the whole size thing. As I want to be able to give my clients enlargements if they want etc.

Or do I just convert the image to 300dpi and then do the upsize by 10%? But that seems like the "cheats way" and the the way you are suppose to do it?

Any help would be greatly appreciated.

Oh, and by the way I AM SO IN LOVE WITH MY REBEL XT!!!!!

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May 15, 2005

Medium and Small (in Fine or Normal) reduces the pixels. I suspect from your question that you had it set for "Medium/Fine" or "Medium/Normal."

Be aware also that bumping up the "ISO" too high will start to reduce resolution of image capture . . . even if the pixel count remains unchanged.

My personal standard is 425 dpi for fine prints although many find 300 dpi acceptable. At your XT's maximum pixel capture for 300 dpi printing, the maximum print size is about 7-2/3 x 11-1/2 inches. The short side doesn't quite make it for an 8 x 10 inch print which means it may look a slight bit rough at hand held viewing distance (about 14 inches) when compared to something that has 300 dpi across both dimensions and certainly compared to something with 425 dpi on both dimensions. Even so, it's more than a Rebel Digital (no XT) with 6.3 megapixels.

-- John Lind

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May 15, 2005

Medium and Small (in Fine or Normal) reduces the pixels. I suspect from your question that you had it set for "Medium/Fine" or "Medium/Normal."

Be aware also that bumping up the "ISO" too high will start to reduce resolution of image capture . . . even if the pixel count remains unchanged.

My personal standard is 425 dpi for fine prints although many find 300 dpi acceptable. At your XT's maximum pixel capture for 300 dpi printing, the maximum print size is about 7-2/3 x 11-1/2 inches. The short side doesn't quite make it for an 8 x 10 inch print which means it may look a slight bit rough at hand held viewing distance (about 14 inches) when compared to something that has 300 dpi across both dimensions and certainly compared to something with 425 dpi on both dimensions. Even so, it's more than a Rebel Digital (no XT) with 6.3 megapixels.

-- John Lind

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May 15, 2005

Thanks for your feedback. I had it set on Fine/medium, but thought that I would of been able to get prints bigger than that, so I am assuming the only way to get bigger prints (ie if you have it set on fine/large) is to upsize by 10% in Adobe afterwards. I did also take some pics in fine/large but still was disappointed with the size the image was at 300dpi. So 425pdi would even be smaller.

If you have a client who wants a big 16x20 print etc, how do you go about making sure your image can print to that size?

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May 15, 2005

If you want to see what a 16x20 would look like from your camera's maximum resolution, print something you have at 150 dpi (let print dimensions fall where they will for the file size).

There are some interpolation algorithms that smooth out the jagged roughness of pixelation when upsizing . . . but none of them can create detail that isn't there in the original file (some "fractal" interpolation algorithms will "fake it" by "guessing" at what would be there in the missing pixels). I cannot help you with some suggestions about the better ones, perhaps someone else can; I've never had to use them (see next paragraph).

I'm a film user, so I'll give you my perspective on prints that size from a film standpoint. If at all possible, I avoid making a 16x20 from 35mm small format! It can be done with great care using a high quality optical enlarger, if the negative or slide film has high resolution (e.g. slow film speed), and if it was exposed with great care regarding camera shake, critical focus and depth of field (appropriate for that scale of enlargement; apparent DOF shrinks some with enlargement). I don't like going any larger than 11x16 inches from 35mm. For prints destined to be enalarged to 16x20 I use medium format (with high resolution film). At that size it makes an obvious difference. One need only put two well-made prints that size from the same film in 35mm and 645 side by side to see it (I can start to see it in well-made 11x14's), and that's using films like Portra 160 NC, Ultra Color 100, Kodachrome 64, Provia 100F and Velvia 50.

A good friend of mine uses an Olympus E-300 which has similar resolution (2448 x 3264). He doesn't make anything bigger than 8x10 from it (for all the reasons above). We've had several discussions about it . . . including some experiments he did with larger prints . . . and with the effects he noticed the first few times he bumped the "ISO" high to work with available light in low lighting situations.

-- John Lind

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May 15, 2005

Thanks for that, I am a bit dumbfounded really that you can't enlarge more with a 8.3 megapixel camera.

I wonder how my wedding photographer did it, as she included a 16x20 print in our package (and I know she goes bigger than that too) and has a digital Pentax (not sure which one it is though).

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May 15, 2005

As I posted earlier, I'm using film . . . and to reveal more . . . my personal manifesto is along the lines of Group/F64 for most of my work . . . maximum detail of principal subject . . . to achieve an "in your face" realism. Others, quite legitimately, work to a different one. It's a matter of personal style. If we all did everything the same way photography would be boring.

-- John Lind

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May 15, 2005

Use an interpolation program and try 150-200 DPI. Always shoot RAW and upload to Online Print shops that accept TIFF like Mpix. You should be able to get very acceptable large prints this way. There are MANY MANY pro photographers who get excellent large prints from 8MP SLRs...or even 6MP SLRs. Certainly larger than 8x10!!! I got great 8x10 from a 3.2 MP P&S camera.

Karma

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May 16, 2005

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May 16, 2005

I have the 6.3MP Digital Rebel, so my images at max resolution are 2048 x 3072 pixels. The only time I ever change the image size or dpi is when I upload an image to my BP gallery. I "save as" to a "resized gallery" folder, then change the dpi to 72 and the pixels to 500 x 750.

Otherwise, I don't change the size or resolution of my images. My images are 2:3 ratio, so if I'm printing 4x6 or 8x12, I do nothing. After doing any editing, I upload the image to Mpix and select a print size. If I need an 8x10 or 11x14, I crop the image to that ratio and save as "filename 8x10" etc.

Should I be doing something differently?

I don't use PS, but in Digital Image Pro, the dialog for changing the image format has three settings: Image Size (in inches), Pixel Dimensions (in pixels) and Resolution (in dpi). From what I understand, changing any one of these does NOT actually change the information in the image. So when I change the resolution to 72dpi, it just spreads the pixels out to make the image size larger. But when I also change the Pixel Dimensions to 500x750, it actually "throws away" information and makes the image smaller. Am I on the right track here?

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May 16, 2005

I have made 8x10s from the Digital Rebel without a problem (even from cropped sections of images).

I have even taken the Digital Rebel RAW images to 16x20 for a couple of shots.

I see nothing wrong with the 8x10 prints or 16x20 prints from the Digital Rebel.

Thanks,
Robert

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May 16, 2005

interpolation algorithms - can you explain this to me like I am a 2 year old, sorry John, but you could of been talking Greek to me about half of that stuff!

Karma - yes, the print up close is a little hazy and not "sharp" but it still looks beautiful, and again, they aren't meant to be viewed up close, so maybe when I do large prints, I can reduce the dpi down a little.

Chris - I understand what you are doing, this is what I have been doing most of the time, I don't think there is a right or wrong way, just the way you want to do things, if it is working for you, then stick with it! The only thing I do differently is change all my prints to 300dpi straight away in the computer (which in turn reduces their size)

I have also been told by a pro, that you can almost double the size of a print say a 8x10 @ 300dpi, you should be able to double it without it looking too bad (this is probably what my wedding photographer did).

RAW - I am not really familiar with this and not sure what has to be done to the print afterwards, as I shoot about 200 photos in a photoshoot, I don't want to sit there adjusting 200 photo individually. I have a few actions that help me, but I suppose I just need to learn a little more about RAW before I use it.

Thank you everyone for so much feedback, I was overwhelmed when I came into work today!

I really appreciate all your points of view and advice, it is nice to know you can come to a place like this and ask questions and they get answered!

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May 16, 2005

interpolation algorithms - can you explain this to me like I am a 2 year old, sorry John, but you could of been talking Greek to me about half of that stuff!

Karma - yes, the print up close is a little hazy and not "sharp" but it still looks beautiful, and again, they aren't meant to be viewed up close, so maybe when I do large prints, I can reduce the dpi down a little.

Chris - I understand what you are doing, this is what I have been doing most of the time, I don't think there is a right or wrong way, just the way you want to do things, if it is working for you, then stick with it! The only thing I do differently is change all my prints to 300dpi straight away in the computer (which in turn reduces their size)

I have also been told by a pro, that you can almost double the size of a print say a 8x10 @ 300dpi, you should be able to double it without it looking too bad (this is probably what my wedding photographer did).

RAW - I am not really familiar with this and not sure what has to be done to the print afterwards, as I shoot about 200 photos in a photoshoot, I don't want to sit there adjusting 200 photo individually. I have a few actions that help me, but I suppose I just need to learn a little more about RAW before I use it.

Thank you everyone for so much feedback, I was overwhelmed when I came into work today!

I really appreciate all your points of view and advice, it is nice to know you can come to a place like this and ask questions and they get answered!

To love this comment, log in above
May 16, 2005

interpolation algorithms - can you explain this to me like I am a 2 year old, sorry John, but you could of been talking Greek to me about half of that stuff!

Karma - yes, the print up close is a little hazy and not "sharp" but it still looks beautiful, and again, they aren't meant to be viewed up close, so maybe when I do large prints, I can reduce the dpi down a little.

Chris - I understand what you are doing, this is what I have been doing most of the time, I don't think there is a right or wrong way, just the way you want to do things, if it is working for you, then stick with it! The only thing I do differently is change all my prints to 300dpi straight away in the computer (which in turn reduces their size)

I have also been told by a pro, that you can almost double the size of a print say a 8x10 @ 300dpi, you should be able to double it without it looking too bad (this is probably what my wedding photographer did).

RAW - I am not really familiar with this and not sure what has to be done to the print afterwards, as I shoot about 200 photos in a photoshoot, I don't want to sit there adjusting 200 photo individually. I have a few actions that help me, but I suppose I just need to learn a little more about RAW before I use it.

Thank you everyone for so much feedback, I was overwhelmed when I came into work today!

I really appreciate all your points of view and advice, it is nice to know you can come to a place like this and ask questions and they get answered!

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May 16, 2005

Karma

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May 16, 2005

There's a lot of math there . . . but don't worry about it as much as looking at his examples of the effects. I have the advanced education to follow the math, and the scientific principles he discusses, but I know most people don't. In actuality, 300ppi printing is considered at the high end of moderate detail. From a standpoint of human visual acuity, it peaks at about 600ppi. However, the improvement from 300ppi to 600ppi is incremental (i.e. not much) compared to the noticeable improvement made from going from 200ppi to 300ppi. Can one "get away with" 150ppi? Certainly, but don't sit it next to one at 300ppi or 400ppi . . . and display it so as to discourage close viewing. I agree with his printing remarks (having worked out a lot of the human visual acuity limits, print sizes and viewing distances myself). I disagree some with his conclusions about 35mm film comparisons with digital because of the lens he used and its optical limitations for measuring some of the 35mm format limits (lenses have resolution limits) and the aperture at which he used it (f/11; f/5.6 and/or f/8 might have been better). I've found finer detail in 35mm slides than he measured.

Interpolation:
An algorithm is a set of mathematical equations used in a specific manner as a process . . . input information, crank through the math equations, and get output information. An interpolation algorithm as applied to upsizing digital images is a set of equations in a computer program to make the digital file bigger. If you have a 100 x 100 pixel image and want to make it 200 x 200 pixels, you need to add a new pixel between all the existing ones. An interpolation algorithm decides what color and intensity to make the new pixel, based on the colors and intensities of the existing pixels surrounding the area where the new one will be added. The following dpreview article describes the most common ones used for this:
http://www.dpreview.com/learn/?/Glossary/Digital_Imaging/Interpolation_01.htm

The "nearest neighbor" method is by far the simplest, but it's also the worst with photographs as it increases the "jaggies" (makes it look ragged). Bilinear does much better, and bicubic is usually better yet. The most complex are the fractal algorithms. See the excellent examples in the dpreview article that show the effect each of these have when used to upsize a digital photograph. I encourage you to look at using one of the higher end interpolation methods to upsize for larger prints, and maintain a 300ppi printing instead of simply printing a larger print at a lower ppi. I presume it's why you posted your question.

Karma is correct that RAW gives you the greatest flexibility in adjusting contrast, color balance, etc. It's also the most memory intensive. When you shoot a wedding, keep this in mind and plan accordingly with having enough memory to hold it all or with being selective about what you shoot using RAW. Also check out the lag time to record a RAW into memory versus a JPEG. If there is much difference, there may be times with rapid sequences that you cannot afford the delay between shots.

-- John Lind

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May 16, 2005