Can we talk about resolution vs compression?

I am hoping to enlist the benefit of the cumulative wisdom of some of you fellow Canon users. Allow me to explain.

I am pondering the question of in camera pixel resolution selection for images to be printed to paper.

Consider a need to keep image size down to increase the number of pictures stored per CF card, and the goal of making the best print with each image, are you better off with a smaller number of pixels at a higher quality mode, or a larger number of pixels at a lower quality mode.

For example: Printing a 4*6 image, which settings will yield a better result.

MedLow size, Super Fine image quality 570Kb
MedHigh size, Fine image quality 558Kb
Large, Normal image quality 556kb

My gut instinct is to think that when printed, each of these will be equivalent because they amount of information in bytes is very close together. I ask the net because so often I find that what I thought was gut instinct is only indigetsion.

Paul

Hi Paul,

Much of the needed resolution and quality depends on what technology and resolution your printer utilizes - and how big are your prints and how far are you watching them.

If you print with an RGB printer at 1440 dpi, each dot can output one dot in _any_ colour so it's very sharp and clear. CMYK printers (most home printers) recreate an RGB pixel of a matrix of several dots (eye mixes these together from a distance), which means 1440 dpi on an Epson home printer means something like 360dpi in an RGB printer if 4 dots on Epson are used to represent one RGB color.

If you print bigger and view from a close distance you'll need more resolution and RAW source photo or a big JPEG. If you print small and view from far you'll need smaller resolution and can get away with lower compression. You can roughly test this behaviour on your computer screen - just walk further from it and you can see a bad looking photo is acceptable from far -- think now the screen as a piece of paper you're holding: how big would that paper be?

And as always test prints are a good idea before doing any real projects.

Pekka, thanks for your reply. After seeing what you did with your G1, I decided to get one. I waited for the G2, since it's release was so close (actually have one now). I sent you an email regarding the serial number of the pictures. Now that I have the software that comes with the camera, I realize what a dopy question it was. Figured that one out! (just uploaded pic 100-015)

My wife tells me I tend to get a bit windy, (see number of words in above paragraph) and I guess that's the problem with my first post.

Let me rephrase entire first post with one sentence.


Given the SAME number of bytes used in a jpg file, what do you think will produce a better printed picture, a smaller picture with less compression, or a larger picture with more compression?

PJ


btw, Thanks again for the website Pekka. Canon should give you photo hardware as a thanks for selling people on their equipment.

PJ

Larger image size (pixels) means it can store more detail. JPEG compression on the other hand kills detail and color smoothness when used too strongly. But even a good JPEG compression can not produce any new detail, so I'd say the bigger image size (more pixels) will always get you a better print -and take into considering also that in-camera JPEG compression levels are never very strong, even in lowest setting.

If you take a photo e.g. of a tree against a blue sky or any detailed item over graduated color using different compression levels, you can see cleary if there's too much blockyness due strong JPEG and when you feel that the quality is not what you need.

One more word, though: It's always a good idea to shoot with best image quality (largest resolution) - you never know when you get that once in a lifetime shot and how big a print you'll need. A shot can always be downsized and saved in different formats and compression levels. But you can not convert a small over-compressed image to a big sharp and smooth one.

Thanks. If you feel like writing them please go ahead! I really could use some sponsors for getting the latest toys (it's said that the next Canon digital SLR model costs twice the D30!)

But this site is not there for selling Canon cameras. You already have a Canon when you get here, right? I hoped this forum would be more practical in content and have more content than quantity (and without flamewars about technical aspects like in some other forums) and I think it really has been so: the quality of discussions has been high and people really share their knowledge willingly (big thanks to all!).

Pekka

I'm new to this forum, and I found it very informative;
could you please explain, how I can downsize the picture, so it can be sent faster through email. Thanks

What photo-manipulation software have you got?

David

I'm going to risk disagreeing with El General.

If all you want to do is print at 6x4, and you are 100% sure that you will never want to print any larger or crop the image, then there is no value to having more pixels than can be seen on a 6x4 print. The usual rule of thumb for small prints is 300ppi, so that would imply there is no need for an image larger than 1800x1200.

I don't know what JPEG options you have on your camera, but on my 350D I can choose between:

1. Large/Fine: 3456x2304 pixels, approx 3.3 MB (JPEG compression factor 6.9)
   
2. Large/Normal: 3456x2304 pixels, approx 1.7 MB (JPEG compression factor 13.4)
   
3. Medium/Fine: 2496x1664 pixels, approx 2.0 MB (JPEG compression factor 5.9)
   
4. Medium/Normal: 2496x1664 pixels, approx 1.0 MB (JPEG compression factor 11.9)
   
5. Small/Fine: 1728x1152 pixels, approx 1.2 MB (JPEG compression factor 4.7)
   
6. Small/Normal: 1728x1152 pixels, approx 0.6 MB (JPEG compression factor 9.5)

I see little point in using anything other than the maximum resolution available. CF cards are cheap now, really cheap, so there is no excuse for not having enough space to store your pictures. You can throw data away but never get it back.

If you want to have smaller pictures for e-mail for example, just save a copy of the original reduced to the appropriate size in PS or any other photo editing program. You can get a presentable 800x600 (approx) in less than 60K.

Kenny,

Keep in mind that this thread is 5 years old. When the question was origianlly asked, CF cards were running about $3 per meg. (I bought a 32 meg card for $75 and was thrilled.) So yes, you are right, NOW they are cheap. But in the context of when the question was asked, the need to keep image size down to increase the number of pictures stored per CF card was very real. Before I had my 10d (June 03) I used that 32 meg card in a Kodak P&S and SOP was shoot, chimp, delelte, repeat till you get one you like.

Rad

I ran into this info the other day and I am wodering how accurit it is ??

Mimimum required resolution for printing

AdoramaPix automatically reviews digital photo resolutions and compares to the minimum size required to achieve a good print. If a digital photo’s resolution is too low to print well at any size, AdoramaPix will flag it with an indicator in the Album, and will not allow you to place it in a Print Order.
The minimum resolution that we will print is 100 dpi; however for best resolution we recommend 300 dpi. The table below shows the minimum and preferred image resolution for some of our standard print sizes. (Note: pixel resolutions generally list the wider dimension of the image aspect ratio first, so our table shows wider dimension for easy comparing.):
Print sizeOptimal resolution for good print quality (300px per inch)Minimum resolution, less optimal image quality (100px per inch)Lower resolution means less detail contained in the original image, so when photos with low resolution are printed at a large photo size, they will appear blurry and pixilated (blocky with jagged rather than straight edges

hope this helps
go to adorama.com site to see the figures for the above info::

Partly accurate.

300ppi is a reasonable upper limit. Assuming the source image is sharp, which isn't always the case! - something that's printed at 300ppi will look sharp even when examined quite closely.

But the larger the print, the less closely you tend to look at it. A useful rule of thumb is that the 'typical' viewing distance is about 1.5 times the diagonal of the picture. So you can get away with lower resolution - i.e. fewer ppi - for larger prints, because in normal circumstances you won't be looking at them so closely. Take a close look at a large billboard poster some time and you'll see only a few ppi - but it looks fine from across the street.

So if you print an image at 100ppi, whether or not it looks OK depends on how far away you view it, which usually depends on how big the image is. I imagine that this company you've found won't print images that are really really huge, so their 100ppi mimum is probably quite sensible for them.