megapixel and printing question

scamel · Sep 22, 2006

Now I know a bit about photography and Photoshop (maybe not as much as you people here but more than the average Joe Blow in the street) and I've been visiting some photographers for my own up and coming wedding.

This photographer tried to tell me that it's possible to do a wall print from a photo that is only 2 mb. Is this true or not? I'm not sure what it was shot at.. maybe around 4? mp or so?

But her camera has a max of 10 and she was telling me that it doesn't always shoot at that level, it depends what elements are in the photo and the camera will know (or she will select) the right setting so the photos will all be taken at different mp depending on the composition of the photo and hardly ever at the max of the 10??

is this true?? I found this really hard to believe...

thanks.

scamel · Sep 22, 2006

by wall size I mean at least 20x30"

JDP · Sep 22, 2006

You might be able to squeeze 20x30 out of 10MP at 150dpi. To use an example, a 300dpi 13x20" photo (Which means it looks fantastic when you're right up to it) would need about 23MP, at 150dpi (Looks good from arms length) you'd only need about 6mp

And either she, or I, are confused. As far as I know, picture sizes do vary but 10MP is 10MP. The variance is in the jpeg compression (if taken as such) - large amounts of even color (Like a beige wall) take less space then a mosaic of color, because it's easier to condense that info. Something like "Oh, the color 0xFFF0DE goes from pixel 23:1 to 3005:1, so I'll just make a note of it here, instead of copying every single pixel.

Rob · Sep 22, 2006

She's right.... In my opinion anyway.

If you shoot in jpg, and most wedding photographers I know do.... then you will have (with my 8MP camera for example) file sizes between about 1.8 and 5Mb. It is certainly possible to print a 20x30 image from a 2Mb jpg, BUT as with everything, it depends on the image itself.

If you have a very sharp, quality original at low ISO with no dodgy contrast areas (like silhouetted branches) then you will be able to enlarge it very big without any noticeable problems.

With photography I often find that the maths can be utterly irrelevant - megapixels don't really make a difference UNLESS you are comparing the same shot taken at the same time enlarged beyond the theoretical maximum (which is probably around 240dpi) visible dot pitch. If there's nothing to compare to and you're not running a scientific test.... just try it and see how it looks.

Anyone decent with photoshop and perhaps a copy of genuine fractals or similar would have no problem in producing a 20x30 group shot or portrait from a normal 350D/20D/30D/1D/5D or equivilent (assuming the original photo was decent!)

Rob
EDIT: I suspect what she is doing is switching to RAW+jpg for formals and the switching to high/medium quality jpgs for the candids. Normally candids are only shown at 6x4 or 9x6 or thereabouts not blown up big like the formals are... This method would allow the photographer to take hundreds more candids and not worry about filling the card(s) up too quickly.

D-50 · Sep 22, 2006

20x30 from a 2mp seems a but of a stretch you could print it but I think it would lack resolution. I use a 6mp D-50 and find I can print at 300dpi and get a 13x20 that has good resolution. I routinely crop my original files to about 10x4 and then enlarge them to 8x19 and they turn out fantastic.

Big Mike · Sep 22, 2006

I also suspect that she may be referring to switching between RAW and JPEG. My 8MP camera creates large/fine JPEG files in the 3-5 MB range.

Don't forget about viewing distance. I've made 20x30 prints from a 1.3 MP camera and from poorly scanned 4x6 prints on a cheap flat bed...and I printed them on plain bond paper...they looked OK from 8-10 feet away. Not what I would consider great quality...but a 20x30 from a good camera, on good paper, in a nice frame...will look great.

markc · Sep 22, 2006

Megapixels and megabytes are two very different things.

Megapixel refers to a number of pixels (1,000,000 pixels). This only changes with resolution. 3072x2048 is 6.3 MP.

Megabyte refers to a number of bytes (1,048,576 bytes in terms of memory, or 1,000,000 bytes in terms of hard drives and other storage).

The number of pixels will tell you what kind of print you can make from it. The number of bytes only tells you how much room those pixels are taking up on your HD. They say nothing about the print.

The only way to change the MP of an image while taking it is to set the resolution you are shooting the camera at, often labeled as "small", "large", etc. I don't know of any cameras that do this on the fly based on composition. I think she was mixing up the two based on her file sizes.

usayit · Sep 23, 2006

Although this chart is a simplification of the complexities of printing, it is still a good start.

http://www.bhphotovideo.com/FrameWork/charts/resolutionChartPopup.html

There is a whole lot more involved in getting a good print from a digital picture. Here's just a few that comes to mind....

* megabytes, as in file size, is totally different from megapixels. This is especially true with jpeg compression.
* jpeg is a lossy compression algorithm. I find the "artifacts" it leaves behind more noticeable when printing enlargements.. especially anything larger than 8x10. Storage is cheap and the information lost during jpeg compression is not recoverable... hence I shoot raw perform a series of adjustments and store in the largest tiff i can produce. The large tiff is what I archive. When I'm ready to print, I downsize the tiff to between 150-300dpi (see printer documentation) just before printing.
* the number of megapixels required to print to a certain size is HEAVILY dependent on viewing distance. A 20x30 print mounted high on a wall is going to be quite different from an 8x10 print in a book format.
* The amount of final sharpening applied to a picture just before printing is also heavily dependent on size and viewing distance of the photo.

Several years ago when 3mp cameras were the front edge of digital photography, there was a wonderfully displayed 20x30 print of a model's face at a local photolab (IIRC, it was taken with a Canon D30). It was used to showcase the lab's new service to provide professional quality ink jet prints. Up close... you can see that they were pushing the limit of 3mp but no one looks at a 20x30 print at a viewing angle of just about 1 foot. At a viewing angle of just over an arms length... the print was more than acceptable.

scamel · Sep 23, 2006

Thanks for your thoughts and opinions.

I wish I remembered the image size in pixels but I can't. I think it MAY have been around something like 2000x3000. It was also 180 dpi when opened in photoshop.

Is that possible for a 2 Mb image?

scamel · Sep 24, 2006

anyone?

Tiberius · Sep 25, 2006

To get the size in Megapixels multiply the pixels in the width by the pixels in the height. Basic geometry. A 2000x3000 picture would be 6,000,000 pixels - 6MP. A 2MP image would be 1600x1200 more often than not, I would bet.

usayit · Sep 25, 2006

He said... 2 Megabytes not 2 Megapixels.

Difficult to say once compression is taken into consideration... not all images compress in the same manner.

markc · Sep 26, 2006

You can't go by MB or DPI. Only MP gives you real information. Even then it will vary depending on viewing distance, the viewer's eye and how much they care about details, etc.
http://www.rideau-info.com/genealogy/digital/dpi.html

Here's my rule of thumb: Set the image print size without resampling the image (8"x12" or whatever). Don't change the pixel count. The DPI should now change. If the DPI is near 300 or higher, you should get a great print. If it's above 150, you should get a print good enough at a distance, not so picky people, or some grainy images. If it's 100 or lower, you should probably choose a smaller print size.