Quick question...

BoblyBill · Dec 9, 2006

If a camera (ie. canon 10d for excample) says 6.3 MP, what is the DPI of the print? If I take a RAW picture and I upload it in PS what is the default dpi? 300, 96, 72?

Any help would be greatful.

BoblyBill · Dec 9, 2006

does anybody know? Or am I not asking the question right... confused?

BoblyBill · Dec 9, 2006

The reason that I'm asking is I'd like to get into the digital realm, but I don't have the money for alot... I was looking at the Canon d30 that is 3.1 MP which is a little bigger than what I usually get my files from my scanned negatives. The scanned negatives are 1818x1228 at 96 dpi and I can get a rather good 8x10 out of them... I have scanned some of my slides at home (cause I can't afford to have someone do them for me) and I have gotten 4852x3245 at 600dpi but the image has lost some sharpness. This Canon d30 can do 2160x1440 which will work for me as long as I can get a good 8x10 out of it (since I'm not good enough to sell them the cost of film and developing is killing me.)

oldnavy170 · Dec 9, 2006

Sorry, I can't help but I didn't want you to feel ignored....

BoblyBill · Dec 9, 2006

Thank you Oldnavy, thanks for the reply... I was beginning to wonder.

Torus34 · Dec 10, 2006

You are confusing two different concepts here.

Let's deal with megapixels first. A 6.0Mp image is a matrix of individual 'dots.' The number of individual dots is the number of dots in a row times the number of dots in a column. In the case of 6Mp, the rows are about 3000 dots long and the columns about 2000 dots high ['landscape' image.]

That's the image your camera takes and stores on the chip.

When you print out an image, the printer creates an image of dots, too. This is usually stated simply as dots per inch for each line printed. It depends on the printer and the 'quality' level selected for the print.

So far, so good.

If you print out a picture from your camera, and if it was taken at the 3000x2000 pixel setting [maximum definition], and if you print it as a 10 inch wide by 6.666 inch high print, and if you use a 300 dot per inch [DPI] printer, each pixel in the image will be represented by one 'dot' in the printed image. [10 inches x 300 DPI = 3000 'dots.'] This is the maximum definition you can get from the original stored image. A print larger than this will spread the detail out to make up for the larger image.

If you print out a picture from your camera, and if it was taken at the 3000x2000 pixel setting [maximum definition], and if you print it as a 5 inch wide by 3.333 inch high print, and if you use a 300 dot per inch [DPI] printer, every four pixels in the image will be represented by one 'dot' in the printed image. That's 4 pixels, not 2. That's because you've also compressed the height as well as the width of the print. The print will be 'sharp', but some detail has now been 'averaged' out of the image.

That should be enough to get you started. Mull it over, and then ask again if you need further information.

mysteryscribe · Dec 10, 2006

Now trust me on this Im no expert but when digital was in it's infancy... The best affordable cameas were 3.5 and 4 mega pix. I tried out the idea of digital for my son in law. He had just taken over my studio and I had the time and resources. He was shooting 645 film at the time.

I made several 8x10 prints that were very satisfactory from a full frame 3.5 megapix camera. The 4megapx looked about the same. I even did just a couple of business prints for preachers and real estate types. I think the main problem with low mega pix files comes when you crop them or try to go larger than they are designed to do comfortable. The same is true of 35mm by the way.

DPI comes into play when you print them or when you scan a print or negative. But the explaination above covers the details of it all.

I have also heard a file should be large enough to do the size of the print @ 300 dpi. I never had a customer who seemed to know the difference between 300 dpi prints and 200 dpi prints. At 200 dpi printer file resolution you can get more size from the megapix you have.

Its all rather confusing I know. It is for me and I tinkered with it when it wasn't even popular.

markc · Dec 10, 2006

http://www.rideau-info.com/genealogy/digital/dpi.html

BoblyBill · Dec 10, 2006

Torus34 said:
You are confusing two different concepts here.

Let's deal with megapixels first. A 6.0Mp image is a matrix of individual 'dots.' The number of individual dots is the number of dots in a row times the number of dots in a column. In the case of 6Mp, the rows are about 3000 dots long and the columns about 2000 dots high ['landscape' image.]

That's the image your camera takes and stores on the chip.

When you print out an image, the printer creates an image of dots, too. This is usually stated simply as dots per inch for each line printed. It depends on the printer and the 'quality' level selected for the print.

So far, so good.

If you print out a picture from your camera, and if it was taken at the 3000x2000 pixel setting [maximum definition], and if you print it as a 10 inch wide by 6.666 inch high print, and if you use a 300 dot per inch [DPI] printer, each 'dot' in the image will be represented by one 'dot' in the printed image. [10 inches x 300 DPI = 3000 'dots.'] This is the maximum definition you can get from the original stored image. A print larger than this will spread the detail out to make up for the larger image.

If you print out a picture from your camera, and if it was taken at the 3000x2000 pixel setting [maximum definition], and if you print it as a 5 inch wide by 3.333 inch high print, and if you use a 300 dot per inch [DPI] printer, every four 'dots' in the image will be represented by one 'dot' in the printed image. That's 4 dots, not 2. That's because you've also compressed the height as well as the width of the print. The print will be 'sharp', but some detail has now been 'averaged' out of the image.

That should be enough to get you started. Mull it over, and then ask again if you need further information.

I understand the math behind the dpi. I was asking you guys out there with digital cameras what your files look like when you place them into your computer. Take the Canon 30d for excample, I know that some of you guys have one. So when you place the file onto you computer, the file, in RAW, is a 3504 x 2336 at ? dpi... Do you chose the dpi once you put it into you computer? Or is there a set dpi that all you files come out at as? I ask this because if I had a picture that was a 3000x2000 at 1dpi and I had the same picture but it was 27000x18000 at 18dpi and both were set side by side and both were 1000 ft wide and 666.66 ft heigh, you could get closer to the 1000 ft. x 666.66 ft. picture if it was a file that was 27000x18000 at 18dpi because there is twice the dot per inch. I'm sorry if I'm not making myself clear at what I want. Thanks for all you help. I'll try to explain myself better next time

markc · Dec 10, 2006

DPI means nothing in a file. It only has bearing when you print. A 3504 x 2336 pixel file at 1 dpi is exactly the same as one at 1000 dpi. When printed the 1 dpi file will be 3504 x 2336 inches, while the 1000 dpi file will be 3.5 x 2.3 inches, but they are made up of the same number of pixels. In this case, it really should be labeled PPI, for pixels per inch.

Torus34 · Dec 10, 2006

The image recorded on the memory card of the camera has no, repeat, no inherent DPI. You can convert pixels to DPI only when you define the size of the print you wish to make from the chip data. If you have a chip image of 3504 x whatever pixels, you can get a DPI figure by dividing the 3504 by the width of the print. A 5" wide print would be 700 DPI. A 10" wide print would be 350 DPI. a 20" wide print would be 175 DPI.

The PRINTED image, however, will be printed at the DPI of the printer, regardless of the pixels in the image row and regardless of the size [width] of the print.

You can have a 1000Mp chip image, but if you print it with a 300 DPI printer setting, the image will be 300 DPI.

BoblyBill · Dec 10, 2006

Torus34 said:
The image recorded on the memory card of the camera has no, repeat, no inherent DPI. You can convert pixels to DPI only when you define the size of the print you wish to make from the chip data. If you have a chip image of 3504 x whatever pixels, you can get a DPI figure by dividing the 3504 by the width of the print. A 5" wide print would be 700 DPI. A 10" wide print would be 350 DPI. a 20" wide print would be 175 DPI.

The PRINTED image, however, will be printed at the DPI of the printer, regardless of the pixels in the image row and regardless of the size [width] of the print.

You can have a 1000Mp chip image, but if you print it with a 300 DPI printer setting, the image will be 300 DPI.

That makes a whole lot of sense!!!!!!!!!!!!!!!!!!! I was thinking about this all backwards!!!!!!!!!!!!!!!!!!!!!!! I'm such a retard... Thank you all who have had the patience to explain that to me... So my 3.1 (2160x1440) MP D30 would be able to print out a 12x8 at 180 dpi right? I think I'm getting it now.

Torus34 · Dec 11, 2006

No such thing as a 'retard' -- just people who haven't yet gotten their minds around a particular concept.

You're getting there.

'my 3.1 (2160x1440) MP D30 would be able to print out a 12x8 at 180 dpi'

Yes! That would be the 'quality' measure of the image your 'puter' would feed to the CRT or printer. It is a definition of the 'sharpness' or lack of 'graininess' in the image. [Higher DPI = sharper/less grainy/higher quality image.

If the printer was also set to 180 DPI, one pixel of the image would become one printer 'dot.' If the printer was set for, say, 360 DPI, it would use a square of four ink 'dots' for each image pixel. If the printer was set for, say, 90 DPI, it would use one ink 'dot' to print each square of 4 image pixels.

That's all there is to it.

The_Traveler · Dec 11, 2006

Without having anything substantive to add, I would like to comment that as a noobie here, it is encouraging to read this series of good natured, helpfu and intelligent responses.

TT

Torus34 · Dec 11, 2006

Welcome, Traveler. And for the participants in this thread, I thank you for your nice comment.

Newcomers to photography have all sorts of details to sort out. It isn't necessarily easy. [Consider the shutter speed/lens opening/depth of focus relationship, for example.] Sometimes the 'Aha!' moment doesn't occur for quite a while. I can still remember, years ago, working my way laboriously through the 'Zone' concept in b&w photography. Getting it straight took a while.

Hope you enjoy TPF. Lots of great folks here.