How many megs gives you what size picture?
Discussion
Hi,
I was thinking of ordering some large prints of some of my photos and was wondering if anyone knew if there was a guide that can help me decide what maximum print sizes I can acheive from a certain size photo?
for example 1MB = A4 2MB = A3...etc etc (not that these are right but the type of format I was hoping to find somewhere, up to A0 and maybe higher)
Cheers
Woody
I was thinking of ordering some large prints of some of my photos and was wondering if anyone knew if there was a guide that can help me decide what maximum print sizes I can acheive from a certain size photo?
for example 1MB = A4 2MB = A3...etc etc (not that these are right but the type of format I was hoping to find somewhere, up to A0 and maybe higher)
Cheers
Woody
You can work it out from the DPI (dots per inch)that you intend to print at. So if you want to print at 150 dpi, a 12 meg image is 4272 pixels on the long side (for the canon 450d at least), which then works out as (4272 / 150) = 28 inches. A1 is 33 inches on the long side... A2 is 23 inches.
Working in reverse... A2 at 23 inches, 150 dpi gives a pixel count of 3450 on the long side. Standard sensors have a 1.5 ratio, so the short side is 3450/1.5 = 2300 pixels. Total megapixel count would then be 3450 x 2300 = 7,935,000 or just under 8 megapixels.
The question is what quality you want to print at. For a poster that you stand some distance from, you don't need such a high DPI. A standard photo print is usually around 300 DPI, large advertising hoardings are at something like 40 dpi.
Working in reverse... A2 at 23 inches, 150 dpi gives a pixel count of 3450 on the long side. Standard sensors have a 1.5 ratio, so the short side is 3450/1.5 = 2300 pixels. Total megapixel count would then be 3450 x 2300 = 7,935,000 or just under 8 megapixels.
The question is what quality you want to print at. For a poster that you stand some distance from, you don't need such a high DPI. A standard photo print is usually around 300 DPI, large advertising hoardings are at something like 40 dpi.
depends on the image - for example fine detail at 150dpi will show pixellation, but a softer image would be ok. as mentioned above, the distance you view at is also a big factor, and you won't be looking at an A2 print up close like you do with a 6"x4" photo. So if it's for a wall hanging large-ish print then 150dpi is fine, but for a photobook or something like that I would go higher (ie 250dpi or higher).
Griftwood said:
so taking a random photo out of my work my pictures its only 3.5meg at 4000 x 3000, all its good for in print is 13" x 10"..... would that be about right 
?
Oh, ok... when you say meg you mean megabytes - ie. file size on the computer.? Edited by Griftwood on Wednesday 30th July 14:05
When I was talking about megs, I meant megapixels.
File size is fairly irrelevant - different images will come out at wildly different file sizes(*). The important factor is the pixel count.. 4000 x 3000 = 12 Megapixels and at full photo quality, that would be fine at 13" x 10".
However, it'll probably look pretty good at double that size (ie. 150dpi). I think I'm right to say that 150 dpi is the sort of quality you'd get in a normal magazine - so you can see it's not as good as a photo, but certainly not unpleasant to look at. So, 150 dpi would give you 26 x 20 inch, or A3 quite comfortably.
(*) Unless your file is compressed to hell, in which case it'll look blurred on screen and messy in print.
Tuna said:
(*) Unless your file is compressed to hell, in which case it'll look blurred on screen and messy in print.
oh ok! I guess if I'm taking pictures as RAW nothing will be compressed,the 3.5 meg was a JPEG - compressed RAW btw..only an expample...but why would it keep the same number of pixels if it was compressed? What does it reduce if not the amount of pixels to get to 3.5meg?Griftwood said:
Tuna said:
(*) Unless your file is compressed to hell, in which case it'll look blurred on screen and messy in print.
oh ok! I guess if I'm taking pictures as RAW nothing will be compressed,the 3.5 meg was a JPEG - compressed RAW btw..only an expample...but why would it keep the same number of pixels if it was compressed? What does it reduce if not the amount of pixels to get to 3.5meg?JPEG images use some pretty amazing maths to represent your image in way that looks _almost_ exactly the same to a human as the original in a much smaller filesize:
http://en.wikipedia.org/wiki/JPEG
Compressed RAW files often use 'lossless' compression (like a zip file) which is a way of saying that they represent the exact original data in a way that uses less disk space, but allows the original data to be reconstructed later:
http://en.wikipedia.org/wiki/Lossless_data_compres...
Griftwood said:
so taking a random photo out of my work my pictures its only 3.5meg at 4000 x 3000, all its good for in print is 13" x 10"..... would that be about right ?
I'd say a big no? Edited by Griftwood on Wednesday 30th July 14:05
I have printed 4meg pictures (2289X1712) to a1 and they look great, it all depends on how close you get (have a look at an oil painting close up and then stand back you'll get the idea)
Just to try to clarify things...
The main thing that really decides how big an image can be printed is pixel count, which isn't changed by compression or file format. Pixels translate to detail - the more detail you have, the bigger you can print it.
The second factor is compression. If the image is saved as JPEG, the compression will introduce small changes in the image. That's particularly visible around sharp edges and areas of high contrast. Here are a couple of examples (magnified so you can see the detail):
The image should look like this:
But JPEG adds in the speckles and mushyness you can see here:
If you turn JPEG compression up high, you get smaller file sizes (still the same numbers of pixels though), but the noise gets worse. Editing and resaving a JPEG image multiple times has the same effect (each save will add more noise). File size does not indicate compression level though - the more detail there is in the original picture, the harder it is to compress it, so the larger the file tends to be. The compression level is something you can set in most photo editing software, and is usually fairly conservative - and good enough for casual printing. Once an image is saved though, the noise is in there, so reducing the compression and resaving won't help you.
The end result of all this is that high compression can mean that the image gets mushy, which will be visible if you print it large enough. On the whole though it's unlikely to be bad enough to worry about if you're printing at around 150 DPI or higher. Photo professionals will probably be sighing in disgust at that, but for the casual amateur I think it's a fair enough rule of thumb.
The main thing that really decides how big an image can be printed is pixel count, which isn't changed by compression or file format. Pixels translate to detail - the more detail you have, the bigger you can print it.
The second factor is compression. If the image is saved as JPEG, the compression will introduce small changes in the image. That's particularly visible around sharp edges and areas of high contrast. Here are a couple of examples (magnified so you can see the detail):
The image should look like this:
But JPEG adds in the speckles and mushyness you can see here:
If you turn JPEG compression up high, you get smaller file sizes (still the same numbers of pixels though), but the noise gets worse. Editing and resaving a JPEG image multiple times has the same effect (each save will add more noise). File size does not indicate compression level though - the more detail there is in the original picture, the harder it is to compress it, so the larger the file tends to be. The compression level is something you can set in most photo editing software, and is usually fairly conservative - and good enough for casual printing. Once an image is saved though, the noise is in there, so reducing the compression and resaving won't help you.
The end result of all this is that high compression can mean that the image gets mushy, which will be visible if you print it large enough. On the whole though it's unlikely to be bad enough to worry about if you're printing at around 150 DPI or higher. Photo professionals will probably be sighing in disgust at that, but for the casual amateur I think it's a fair enough rule of thumb.
Edited by Tuna on Thursday 31st July 22:45
Tuna said:
You can work it out from the DPI (dots per inch)that you intend to print at. So if you want to print at 150 dpi, a 12 meg image is 4272 pixels on the long side (for the canon 450d at least), which then works out as (4272 / 150) = 28 inches. A1 is 33 inches on the long side... A2 is 23 inches.
Working in reverse... A2 at 23 inches, 150 dpi gives a pixel count of 3450 on the long side. Standard sensors have a 1.5 ratio, so the short side is 3450/1.5 = 2300 pixels. Total megapixel count would then be 3450 x 2300 = 7,935,000 or just under 8 megapixels.
The question is what quality you want to print at. For a poster that you stand some distance from, you don't need such a high DPI. A standard photo print is usually around 300 DPI, large advertising hoardings are at something like 40 dpi.
Sorry Tuna you are getting DPI confused with PPI. PPI is what determines the size of the print from the oringinal resolution. DPI refers to the quantity of ink laid down by the printer.Working in reverse... A2 at 23 inches, 150 dpi gives a pixel count of 3450 on the long side. Standard sensors have a 1.5 ratio, so the short side is 3450/1.5 = 2300 pixels. Total megapixel count would then be 3450 x 2300 = 7,935,000 or just under 8 megapixels.
The question is what quality you want to print at. For a poster that you stand some distance from, you don't need such a high DPI. A standard photo print is usually around 300 DPI, large advertising hoardings are at something like 40 dpi.
See article.
http://www.digicamguides.com/print/ppi-print-size....
Peter
Road2Ruin said:
Sorry Tuna you are getting DPI confused with PPI. PPI is what determines the size of the print from the original resolution. DPI refers to the quantity of ink laid down by the printer.
See article.
http://www.digicamguides.com/print/ppi-print-size....
Peter
Hmmm.. if you're a print professional, that's true. See article.
http://www.digicamguides.com/print/ppi-print-size....
Peter
However, most photo editing software refers to DPI, and your computer screen settings refer to DPI. In these cases the 'dot' in dots per inch is accepted as meaning a pixel, so DPI is directly equivalent to PPI. Try it in Windows - right click your screen, select properties, then the settings tab, then click advanced. On the general tab you tell windows the DPI for your monitor, not PPI. I followed that convention because discussing the subtle differences between the two would only confuse matters.
If you send something to be printed, or set up your printer to print something, you will find yourself specifying 'dots per inch', and most people (and software) will understand that in this case the dot being described is a pixel in your original image.
The term PPI is really being pedantic about something that doesn't really have to be made any more complicated than it already is :-)
Gassing Station | Photography & Video | Top of Page | What's New | My Stuff