Can we talk about MPs and Resolution?

[MikeandReneePlus5]

I've tried to read all I can and have learned a bunch but hoped to bounce some things off you fine folks and get some feedback -

1. Resolution is pixels wide X pixels high. ok. My Canon t2i is 18MP so it shoots 5184 X 3456 or roughly 18 MP....is that how that works? But that's in RAW, correct? So how come the RAW file sizes are rountinely 20+MB?

2. If I shoot JPEG the camera will process the RAW image and throw it away and compress things. Ok. But according to the camera specs that JPEG on L/Fine is still 5184 X 3456 but now it's around 6.5MB. What gives? what gets thrown away?

3. For reasons I don't need to understand (low res medium vs high res medium) it is possible to display a photo beautifully on the computer monitor at a lower "resolution". What does this mean? If I resize a photo to 1024X768 that's a 786kb resolution?

4. What does Flickr, Photobucket, SmugMug do to my photos when I upload them? do they resize upon upload? How does this work if I want prints then? I can't print a 1024*768 and have it look good can I? so how do they do it?

5. I had a free photo book from Adorama so I opened their utility and dragged some stuff from Flickr into it. It wouldn't let me size the photos any bigger than 4*6 or maybe it was 5*7. the warning said the resolution wasn't high enough. these were 6.5MB Jpegs when I uploaded them to Flickr...so I guess my answer to number 4 is they do resize them?

6. I've read a bunch in Scott Kelby's Book on Digital Photography (I think Volume 2) that 10-12MP cameras are really for professionals printing posters. He says resolution is really just a means to convey what you can print at and if you are printing up to 8*10 you don't need anything greater than 8MP. Is this correct? so what's the point of a 18MP camera? Does it just give you more data for editing in LR or Photoshop?

I realize that's a ton of questions. Don't feel the need to answer them all I just thought I'd toss them all out and see if anyone can help me get a little further down the road on any aspect of this.....

 

[wbeem]

1: Don't confuse MegaPixels with MegaBytes. The two aren't the same, meaning that one pixel does not correlate to one byte of storage. Remember there is other data included in that RAW file beyond the pixels.

2: The camera processes the image and applies whatever settings you selected (vivid, B&W, etc) and saves the final product as a JPEG. The size and quality of the JPEG depends upon your settings. The rest of the RAW data captured gets discarded, so it doesn't have to be written to the card.

3: Your computer monitor may look fine at 72 DPI, but a print would look horrible at that resolution. It takes fewer dots per inch to display on screen.

4: Each site may vary. A photo site like SmugMug will want to preserve your file's integrity to sell prints. Facebook, however, will compress the hell out of your photos and destroy quality.

5: Don't know the details of the Adorama free stuff. However, if it says the resolution isn't high enough, it could be referring to DPI rather than pixel dimensions. Just a guess.

6: Yes, it's correct. I shoot with a 12 mp camera and print just fine at 36x48 on metal. Perhaps it could print larger, but I haven't tried. My next camera will likely have 36 MP. It's overkill and uses a lot more space on my card. On the other hand, it gives you plenty of room to crop.

 

[zackiedawg]

1. Resolution is pixels wide X pixels high. ok. My Canon t2i is 18MP so it shoots 5184 X 3456 or roughly 18 MP....is that how that works? But that's in RAW, correct? So how come the RAW file sizes are rountinely 20+MB?

You are mixing up two measurements - megapixels and megabytes. The megapixels are as you listed - the number of pixels high by wide that make up the shot. The megaBYTES are how much data storage space the file takes on your computer. RAW files are always significantly larger MB because of all the additional data stored in the file.

2. If I shoot JPEG the camera will process the RAW image and throw it away and compress things. Ok. But according to the camera specs that JPEG on L/Fine is still 5184 X 3456 but now it's around 6.5MB. What gives? what gets thrown away?

Essentially, the thrown away bits are the unused or deemed unnecessary data - for example, white balance is chosen and applied, so all the optional color balances are thrown out - with RAW, all those are still stored in case you decide to alter them in processing. Many more bits of color information remains so you can alter the desired output more dramatically, whereas in RAW, the color information is decided and applied, and the alternate information that wasn't used is tossed out. This makes the physical dimensions (MP) of the photo identical, but the storage data size much smaller.

3. For reasons I don't need to understand (low res medium vs high res medium) it is possible to display a photo beautifully on the computer monitor at a lower "resolution". What does this mean? If I resize a photo to 1024X768 that's a 786kb resolution?

Of course it's possible to have less resolution and still have a lovely photo. For example, if you have a hi-def TV, you're looking at only 1080 lines of resolution horizontally, often on a screen 3-5 feet high...you don't hear many complaints of how bad the picture looks. This is because you're usually viewing it from quite some feet away. Even a fairly low res photo, like a 2MB photo filling a computer screen set to a low resolution such as 1024x768, will look lovely from a few feet away. Too many folks get wrapped up in having the most megapixels possible, but they fail to consider how they'll be using the photo. Virtually any monitor made displays far below the actual physical dimensions of a digital photo - even a very high-res LCD panel will be set to a resolution of 1900 or so pixels wide...and your typical 5MP photo is already at 2500+ pixels wide. Where the extra MP comes in handy is for cropping, or for retaining good detail when resizing to adjust to a lower res print or monitor, or in allowing for the rare large print or super-high-res display.

4. What does Flickr, Photobucket, SmugMug do to my photos when I upload them? do they resize upon upload? How does this work if I want prints then? I can't print a 1024*768 and have it look good can I? so how do they do it?

Most of them allow you to upload full size photos - it's up to you to send them whatever file size you want. They will usually then DISPLAY the photos at a lower resolution, but give you the viewing option to see a larger, or even original size, file. When printing, they will always use the largest size file (original) that you sent them. So it's up to you to upload the larger files if you intend to print from them. Note that some folks don't like to load full size photos online for fear others can steal them and sell them for profit...so you need to decide whether or not you want to print from these online places, or if you want to upload your photos to be viewed 'publicly' or just personally. For example, I use PBase to store my online galleries, for display, online sharing, posting to forums, and for getting interest from clients for sale or publication, however I never upload larger than a 1024 pixel wide photo. Therefore, I don't make prints from my online stored versions - I print from the originals that I keep at home stored on my computer or backup drives. The online versions are just a 'display' copy - clients wanting a photo e-mail me and let me know, and I can send them the full size originals or make prints for them.

6. I've read a bunch in Scott Kelby's Book on Digital Photography (I think Volume 2) that 10-12MP cameras are really for professionals printing posters. He says resolution is really just a means to convey what you can print at and if you are printing up to 8*10 you don't need anything greater than 8MP. Is this correct? so what's the point of a 18MP camera? Does it just give you more data for editing in LR or Photoshop?

Well it's generally correct - actually, you can make lovely 8x10 prints even from as little as 5MP. I've even made nice looking 8x10 prints from 2MP. But as I mentioned above, viewing distance is key - if it's going to be analyzed from 5 inches away with a magnifying glass, the 2MP 8x10 prints won't look as nice as the 5MP 8x10 prints. There is a point of diminishing returns, where more MP doesn't improve a smaller print...certainly an 8x10 print isn't going to show an advantage generally for a 24MP photo over an 8MP photo. However, there's more to the increased resolution than that. A 24MP photo for example can be significantly cropped, and still yield enough resolution for an 8x10 print. That lion that is a small spot in the 8MP print can be cropped in tighter, to fill half the print from the 24MP photo and still yield good enough resolution and detail to match the quality. There are also many variables, like how resizing a larger MP photo can often result in clearer details, sharper results, reduced noise, etc. But it's not just about the megapixels...it's about the sensor size AND the megapixels. 24MP on a tiny little P&S sensor means the megapixels are itty bitty little microscopic things...24MP on a full-frame DSLR sensor are many times larger, absorb far more light, and can deliver far better quality.

Others I'm sure can get into the technical details - but hopefully that gives you an overview and some ideas.

 

[hakepb]

I think one of the more obvious examples of more information in RAW vs JPG is blown highlights. Straight out of the camera, those over exposed areas are white. But the sensor is capable of capturing "whiter than white" (more light wavelengths than your eye can process)
If you have a RAW photo, then in post processing, you can recover most of the detail in those "blown" areas by shifting "whiter than white" down to just white.
JPG, on the other hand, only cares about what a typical human can see, so one of the first things JPG does is drops all "whiter than white" information, so it is usually impossible to fully recover areas of blown highlights from jpg's.

It's similiar how a studio mastered CD has more information than a MP3. One of the first things a MP3 drops are the sounds that are above or below the average range of human hearing. That extra information does crate a difference on a high-end system (ie bass you only feel) despite a good MP3 sounding very enjoyable to an average person)

The biggest problem with JPG is it is Lossy compression. Every time you edit a JPG and save it, the newly saved version has less information than the original. That's why people will convert to a TIFF, finish editing, then save as a JPG.

 

[MikeandReneePlus5]

Seriously awesome info guys. Many thanks.

As Homer would say D'OH! on the MP MB confusion thing. I'm actually not THAT bad at tech stuff...I just brain locked there. Now it all clicks.

I see now on Photobucket/Flickr what you guys are saying. On the FREE accounts you only get web sized images. On the PRO account you can upload up to 20 MB per image and they keep it behind the scenes and display the web sized image.

I think what happened on Adorama is they were probably just somehow linking or grabbing the lower resolution display photo from Flickr, rather than the underlying full version. I'll call them and sort it out. Actually, I probably won't because I'll use Blurb via LR4 from now on and that should grab my full res photos right off my hard drive.

 

[photo_chick]

I know most of what you asked was answered, but you had some questions in there about printing and DPI (or PPI). One thing that hasn't been said is that DPI, for our purposes these days with digital, is mostly used as a translation from pixels to inches (or metric if you swing that way). Understanding how it works comes in handy when you go to print a given size, like 8x10 for example, what size pixel dimensions you'd need. And that's a pretty handy thing to know. There's a formula, inches x DPI = pixels.

Here's a really great article from iStockphoto from a few years ago that talks about DPI and printing that explains it pretty well. Even if it's clicked for you already maybe someone else who comes along will find it useful.

http://www.istockphoto.com/article_view.php?ID=199

 

[boBQuincy]

I've tried to read all I can and have learned a bunch but hoped to bounce some things off you fine folks and get some feedback -

1. Resolution is pixels wide X pixels high. ok. My Canon t2i is 18MP so it shoots 5184 X 3456 or roughly 18 MP....is that how that works? But that's in RAW, correct? So how come the RAW file sizes are routinely 20+MB?

Resolution is by definition the number of pixels. In that regard the RAW and JPG are the same. However, JPG is 8 bits of brightness levels while RAW is usually 12 or 14 bits, either 16x or 64x as much information! Besides less bits JPG also works in 8x8 pixel blocks so even though the files have the same resolution the JPG may have less clarity.

2. If I shoot JPEG the camera will process the RAW image and throw it away and compress things. Ok. But according to the camera specs that JPEG on L/Fine is still 5184 X 3456 but now it's around 6.5MB. What gives? what gets thrown away?

What gets thrown away are any brightness levels that do not fit in the 256 available levels (8 bits). Let's say the file contains a dynamic range of 12 stops and 4096 levels (12 bit RAW). JPG will keep the full 12 stops of range but compress this to 256 levels (8 bits). To simplify things this means each JPG level is now compressed from 16 levels of the RAW file (and this is a big oversimplification). This can lead to banding in areas where the levels are similar, especially in further editing.

3. For reasons I don't need to understand (low res medium vs high res medium) it is possible to display a photo beautifully on the computer monitor at a lower "resolution". What does this mean? If I resize a photo to 1024X768 that's a 786kb resolution?

Monitors are transmissive while prints are reflective, because of this monitors have a much greater dynamic range than a print. The color gamut is generally larger as well although we can print some colors that we can't produce on most monitors (like a bright yellow). Even though the pixels per inch are lower (usually about 96 for monitors) the printer has to mix ink dots to reproduce most colors so the rated DPI is not always what we actually get.

4. What does Flickr, Photobucket, SmugMug do to my photos when I upload them? do they resize upon upload? How does this work if I want prints then? I can't print a 1024*768 and have it look good can I? so how do they do it?

I can't answer that since I don't use those services.

5. I had a free photo book from Adorama so I opened their utility and dragged some stuff from Flickr into it. It wouldn't let me size the photos any bigger than 4*6 or maybe it was 5*7. the warning said the resolution wasn't high enough. these were 6.5MB Jpegs when I uploaded them to Flickr...so I guess my answer to number 4 is they do resize them?

I can't answer that since I don't use those services.

6. I've read a bunch in Scott Kelby's Book on Digital Photography (I think Volume 2) that 10-12MP cameras are really for professionals printing posters. He says resolution is really just a means to convey what you can print at and if you are printing up to 8*10 you don't need anything greater than 8MP. Is this correct? so what's the point of a 18MP camera? Does it just give you more data for editing in LR or Photoshop?

I used to think that, and the rule of thumb is still that 300 pixels per inch is enough to provide all the image quality that is necessary. However, David Dubovoy's essay on resolution (on Luminous Landscape) shows clear evidence that starting with more pixels provides better image quality even when the final image is much smaller than the original. The essay showed how an image from a Phase 1 that originated as 80 MP still looked better at low resolution than an image that originated as 16 MP.

One guess is that the 8x8 pixel crunching that JPG does may be countered by the greater number of pixels, making an 80 MP image that is reduced in JPG about equivalent to a 10 MP RAW (in clarity, not bits). And this is *only* a guess.