72dpi?????

[andrea31419]

I've probably changed something, but for the life of me don't know what. My images, when downloaded are 72dpi? How can I change them to be 300 dpi?

A.

[Jesper]

Andrea,

This is a frequently asked question. The DPI number means nothing - it does not tell you anything about the quality of the photos. The only thing that determines the resolution of a digital photo is the size in pixels, for example 3072 x 2048 pixels.

You don't need to change your photos to 300 dpi.

[jyrgen]

For all practical purposes this dpi means nothing. Your pictures are still the same if you change it.

[jbradc]

I need a little more info to help out, are shoting RAW or JPG? What are using for post processing? (Photoshop, etc...)
DPI does make a big difference if you want to print the photos. See this link for more info...
http://graphicdesign.about.com/library/weekly/aa070998.htm

[andrea31419]

Shooting JPG
Post Processing PS CS

[Hermeto]

Tnx for the link jbradc, cleared out a lot of fog in my head! :D

[PhotosGuy]

I change to 72dpi just in case someone trys to print one. Not sure if it matters, but it makes me feel better! :D

[andrea31419]

I don't want 72dpi, I want to print.

[Curtis N]

We also have an informative thread on the issue in the post processing FAQ sticky.
http://photography-on-the.net/forum/showthread.php?t=83445

[foxbat]

I don't want 72dpi, I want to print.Divide the number of dots along one side of your image by the number of inches along the same side of your printout and cap the result to your printers resolution and that's the dpi you will get at printout.

e.g. a 3072x2048 pixel image printed out at 6"x4" = 512 dpi both horizontally and vertically. If your printer is 600dpi then you'll get a 512 dpi printout. If your printer is 300dpi you'll get 300dpi.

Ignore that 72pi figure you have been given, it's misleading you and is only meaningful to the unresized image shown on your computer monitor.

[SWPhotoImaging]

I think this entire thread is talking about "ppi" (screen resolution), but calling it "dpi", which of course is printer resolution.

[Jon]

I think this entire thread is talking about "ppi" (screen resolution), but calling it "dpi", which of course is printer resolution.
This entire thread is referring to the horizontal and vertical resolution figures which are encoded in the picture's EXIF data, and are reported as "dpi".

[uktrailmonster]

I've probably changed something, but for the life of me don't know what. My images, when downloaded are 72dpi? How can I change them to be 300 dpi?

A.

You've probably just set the print size of your images very large. Check this first.

[Jon]

You've probably just set the print size of your images very large. Check this first.
No, that's what Canon's setting to go into the as-taken EXIF data fields now.

[Titus213]

I change to 72dpi just in case someone trys to print one. Not sure if it matters, but it makes me feel better! :D

Same here.

[robertwgross]

I shoot RAW files exclusively, and my camera can put any sort of DPI tag on them that it wants. At that stage, it makes no difference.

When I do RAW-to-TIF conversion, the converter software is set to change everything to a 300 DPI tag. That may or may not be necessary there, but since my ultimate goal is commonly to print large, then it is convenient to have a 300 DPI tag stuck on them at that stage.

Some printers care about the DPI, and some don't. So, it does not hurt to have a 300 DPI tag or anything else that is sensible, even though it may not be totally necessary.

For contrast, a month or two ago I saw a printing company that wanted customers to set the tag to read exactly 254 DPI. That was kind of interesting.

---Bob Gross---

[Jim_T]

As originally stated, the DPI setting in an image is meaningless..

The DPI setting is recorded in 5 bytes at the header of the image file. There are two bytes used to describe the horizontal resolution (Xdensity) and two bytes used to describe the vertical resolution (Ydensity)...... The fifth byte used to indicate whether these resolutions should be treated as inches or centimters (Units).. If the value of the (Units) byte is zero then it's dots per inch.. If you change the value of this byte to one, then the resolution becomes dots per centimeter.

Changing these 5 bytes has NO effect on the millions of other bytes that actually make up the pixels and ultimately the image.. Changing these 5 bytes does not change the quality of the image or the pixels or anything else... To put it another way.. If you have an image file that's 4 megabytes.. (4 million bytes) and you change the DPI from 72 to 300, all you've changed is 5 bytes in that file.. You've changed nothing else..)

DPI is a PRINTING TERM

These 5 bytes are meant to be read by the software drivers that operate your printer.. They are not an actual part of the image.. They're only a set of instructions that tell your printer how many pixels to spread across each inch of paper... ( The I in DPI stands for inches of paper)...

In other words this is the mechanism that determines the size of the printed output.. DPI is nothing more than pixels divided by inches. A 1000 pixel wide image printed at 100 DPI will be 10 inches wide. A 1000 pixel wide image printed at 200 DPI will be 5 inches wide.. A 1000 pixel wide image printed at 500 DPI will be 2 inches wide............

DPI does NOT have anything to do with how an image looks on a computer monitor.. Rather than explain what's already been explained, I'll post a link to an excellent article on DPI and monitors... http://www.larry-bolch.com/dpi-revealed/


FWIW For the 'C' programers out there, here is the structure of the image header as it's used in JPEG images.


typedef struct _JFIFHeader
{
BYTE SOI[2]; /* 00h Start of Image Marker */
BYTE APP0[2]; /* 02h Application Use Marker */
BYTE Length[2]; /* 04h Length of APP0 Field */
BYTE Identifier[5]; /* 06h "JFIF" (zero terminated) Id String */
BYTE Version[2]; /* 07h JFIF Format Revision */
BYTE Units; /* 09h Units used for Resolution */
BYTE Xdensity[2]; /* 0Ah Horizontal Resolution */
BYTE Ydensity[2]; /* 0Ch Vertical Resolution */
BYTE XThumbnail; /* 0Eh Horizontal Pixel Count */
BYTE YThumbnail; /* 0Fh Vertical Pixel Count */
} JFIFHEAD;

[SWPhotoImaging]

amen

[Titus213]

I change to 72dpi just in case someone trys to print one. Not sure if it matters, but it makes me feel better! :D

FYI - it's what 'Save for the Web' does too.

[UncleDoug]

FWIW For the 'C' programers out there, here is the structure of the image header as it's used in JPEG images.


What did you use to crack the JPEG?

[LittleG.]

Jeez what long, complicated and repetitive answers! :rolleyes:

In PS CS, go to image/image size/, uncheck resample image and make sure constrained proportions are checked (this is important), and replace 72 pixels per inch to 300 pixels per inch (or whatever print res you want). In your printer software you can refine parameter such as 'fit to page', portrait/landscape or whatever. Job done.

If your download software has preference options, then save yourself the trouble on each image, find the relevant options, and choose 300 dpi as default for download. :D

[Jim_T]

What did you use to crack the JPEG?

No, I didn't crack it.. :) Much of the code is available..

Here's a white paper on the JFIF (JPEG) standard if you don't mind technical details and want to read more..

http://www.w3.org/Graphics/JPEG/jfif3.pdf