Mk II File Resolution - Confused

[martcol]

I have just downloaded my first JPEG shots from my 1D Mk II. In Photoshop the Metadata shows File Properties > Resolution: 72 and Camera Data (Exif) > X Resolution: 72.0 then, Camera Data (Exif) > Y Resolution: 72.0.

I take this to mean that the recorded image is 72 Pixels Per Inch. Whatever, the RAW images are shown as File Properties > Resolution: 240 and Camera Data (Exif) > X Resolution: 240.0 then, Camera Data (Exif) > Y Resolution: 240.0.

Can someone explain this for me please? (words of one sylable preferably) It seems to me that the recorded resolution of the JPEGs is low.....

Thanks

Martin

[robertwgross]

The same basic question comes up again and again, but you have asked it a different way.

This is telling you that the JPEG file has 72 dpi print resolution attached to the file, and that doesn't mean anything until you go to print on paper. In your editor, you can change the 72 to be anything. I guess that Canon doesn't think you need to automatically print with any great resolution when you are coming directly from that JPEG.

It is telling you that the RAW file as 240 dpi print resolution attached to the file, and that still doesn't mean anything, and you can edit it to be anything. Canon might think that your RAW would be printed at a finer resolution like 240. For really good prints, you generally like to be at 240-300 or something.

However, those are all print resolutions, and they really don't mean much to the image. You are still shooting at the particular JPEG image resolution, whichever one that is, and you are still shooting at the RAW image resolution, which is the max.

If you felt like it, you could change the JPEG to be 240 and you could change the RAW to be 72, just to be arbitrary.

---Bob Gross---

[Jesper]

Yes, this question gets asked again and again. The meaning of "DPI" and "resolution" is not obvious to most people....

A digital image consists of a matrix of pixels. The only thing that is important is the size of the image in pixels, for example 3504 x 2336 pixels for an image from the 1D Mark II at full size.

The DPI number is not an intrinsic property of the image. It's just a number that's stored along with the image data and it's only a hint that suggests how large the image should be printed in "real world" dimensions (inches). Different programs store a different, arbitrary DPI number in the header of the image file.

When you're finally going to print the image, you'll most likely want to set the DPI number yourself to get it printed at a specific size. The camera software or your RAW conversion software just plugs in an arbitrary number (typically 72, 180, 240, 300), because that software doesn't know at what size you'll be printing the image later.

[robertwgross]

Let me ask the rhetorical question:

What is the best way to solve this problem?

By that, I mean should Canon be asked to change something in the camera settings? Or should Canon re-word something in the manual? Or change something in the menu structure for each camera?

Or, should we here in this forum do something differently to educate new Canon users? The answer is probably hidden in a "sticky" somewhere, but if a new forum member can't find that stuff quickly or easily, then there ought to be a better way.

---Bob Gross---

[martcol]

So, if I can just press this a little further....

The EXIF details are misleading me, right? I do understand the difference between DPI and PPI and that these terms are used incorrectly by some and can be further confused when thinking about Dots Per Inch on an Ink Jet Printer....

It seem as though you are saying that Canon has just attached a number and for some reason chose 72 for the JPEG output. What confused me is that I understand this to be the typical resolution for the computer screen and that this is acceptable because of a VDUs own limitations. No good for printing where nearer 300 DPI seems to be the accepted value.

Is it the case that the image size is what really determines the resolution of the image (i.e. 2544x1696)?

Typical, just when I think I've got my head round something the goal posts get moved!

Thanks for your help.

Martin

[Jesper]

Is it the case that the image size is what really determines the resolution of the image (i.e. 2544x1696)?

Yes. An image is nothing more and nothing less than a matrix of pixels. As I wrote, the DPI or PPI number is not an intrinsic property of the image. Images do not have a resolution in dots or pixels per inch.

When the image is inside the computer or on a memory card, it does not have a "real world" size in inches. Only when you print it, you're getting a print that is X inches wide and Y inches heigh.

For example, if your image is 2544 x 1696 pixels, and you print it so that your print has a size of 8.48 x 5.65 inches, the print will have a resolution of 2544 / 8.48 = 300 pixels per inch. Note that the print has a certain resolution. Not the image itself.

The DPI number, which is stored in the EXIF info, is just a hint that suggests the size at which the image should be printed. Ofcourse Canon doesn't know in advance at what size you want to print your image, so they just put some arbitrary number in there.

[chris.bailey]

Hopefully not confusing matters but in Photoshop the resolution figure does become important as changing any of the size or resolution numbers ( when cropping or re-sizing) results in a re-sample and therefore potentially lost information. I hope that makes sense. Scottes has a wonderful way with words when it comes to Photoshop tutorials, is it worth asking him to have a bash at a piece?

[Scottes]

Jesper really has this covered very well. I'm not sure that I can do any better. Maybe repeating his words with my own...?

DPI/PPI/Resolution is completely meaningless considering an image - a JPG, TIF, RAW, etc. A monitor will display each pixel as a pixel. The resulting size of the image displayed on the monitor depends on the monitor and it's set resolution (1024x768, etc). If my monitor is set to 1024x768 and I look at an 800x600 image then the image will be about 80% as wide as the monitor display. That's 80% whether I'm on a 15" monitor or a 21" monitor. This is not a measure of pixels per inch, it's a simple relationship between the number of pixels in the image and the number of pixels in the monitor. There are no inches mentioned in that relationship.

Monitors display pixels at the size of 1 pixel per pixel. You can change the size of the image displayed by changing the size of the monitor or by changing the resolution setting of the monitor. This has nothing to do with the image. It's still 1 pixel per pixel. You have no control over the size of the pixel on a monitor, although you can change the number of pixels displayed (1024x768, 1280x1204, etc).


When you go to print an image you now have control over the size of a pixel. You can tell the printer to print 1 pixel per inch, all the way up to 2880 pixels per inch (or higher). You now have control of the size of your print by telling the printer the size of each pixel - 300 PPI means each pixel is 1/300". Your image still remains the same because nothing is happening to the pixels in the image - only the size of the print changes. If you set the PPI to 300 you get a nice print, and if you set the PPI to 3000 then you get a wondeful print the size of a postage-stamp. You're in control of the size of the print because you are finally in control of the size of the pixel.


When resampling you are changing the pixels in an image, making the size of the image larger or smaller. You are adding or subtracting pixels. This will change the size of the print, too, since the number of pixels has changed.

When resizing you are changing the PPI and thus the size of the final print. The pixels are still the same pixels - they have not changed. All you have changed is a printer setting - how many pixels to print per inch.

Note that if change the PPI of an image but never print it then you have done nothing, really. You changed a setting, a printer setting, but then you've ignored it by never printing the image.


Does this help at all?

[OviV]

I think it would further be helpful to others to explain the propper way to change this number when you do want to print. This is how I was taught using Photoshop.

First off, if I am going to print an image on my inkjet printer, I have found that 240 DPI is more then sufficient. If I am going to have it printed somewhere like Costco where they use a Fuji Frontier, I set it at 300 DPI.

Here is what I do in Photoshop:

1) Crop image to the appropriate proportions. I do this with the selection tool, not the crop tool. The crop tool does a number of things automatically that you may not want. Set the selection tool style to Fixed Aspect Ratio and set the width and height to the size you would like (i.e. 4x6). Select the crop area and click on Image --> Crop menu.

2) Set the DPI. Click on Image --> Image Size menu. Make sure Resample is UNCHECKED. Enter new resolution (i.e. 300 DPI). You'll notice the width and height will chage when you do this. Do not worry about it.

3) Set printed size. Click on Image --> Image Size menu. Make sure Resample is checked as well as Constraint Proportions, and Scale Styles. Enter desired width under document size and it should adjust the height to the appropriate size automatically.

You now have an image that is sized to a specific height/width for a given Print Resolution. Don't forget to save it with a different name so as to keep your original. I normally use something like CRW_5555_5x7.JPG or something similar.

Ovi

[Scottes]

I do the exact same thing as OviV in every detail.