Contest requirements confusion: pixels vs. DPI

Started 2 months ago | Questions
SunfyreArt Forum Member • Posts: 55
Contest requirements confusion: pixels vs. DPI

Hi everyone!

I'd soon like to enter my first photo contest, but their requirements confuse me a bit:

They want a JPEG image, one side of which needs to be at least 4500 pixels, and its DPI needs to be 300. The winners' photos will be displayed either on a screen or printed at 50 cm x 75 cm or 100 cm x 150 cm.

I know it's possible to change a photo's DPI value without changing its size in pixels.

So, is that really all they want? A garden-variety 72 DPI, (for example) 6240x4160 pixel photo whose DPI has been changed to 300? Ô_o

Thank you!

ANSWER:
NAwlins Contrarian Veteran Member • Posts: 3,577
Stupid requirement but easy to follow
3

I'd soon like to enter my first photo contest, but their requirements confuse me a bit:

They want a JPEG image, one side of which needs to be at least 4500 pixels, and its DPI needs to be 300. The winners' photos will be displayed either on a screen or printed at 50 cm x 75 cm or 100 cm x 150 cm.

I know it's possible to change a photo's DPI value without changing its size in pixels.

So, is that really all they want? A garden-variety 72 DPI, (for example) 6240x4160 pixel photo whose DPI has been changed to 300?

Yes, I think so.

If you edit the file that comes out of the camera, just set it to 300 ppi (incorrectly called dpi by Windows and some other software*) before or when you export the edited file as the JPEG you will submit. If you are submitting a straight-out-of-the-camera JPEG, then check the file's EXIF data, and make sure it's set to 300--again, Widows called it dpi, but it's actually ppi.

This is a stupid, or at least poorly-expressed, requirement from the contest. They ought to say it something like, 'at least 4500x3000 pixels' or whatever. The DPI or even PPI part is needlessly confusing.

*DPI or dpi = dots per inch, and pertains to how inkjet printers spray ink droplets and how certain commercial printing works. PPI or ppi = pixels per inch, and is the correct term to describe the resolution of an image.

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pixelgenius
pixelgenius Senior Member • Posts: 3,063
Re: Contest requirements confusion: pixels vs. DPI
1

PPI has absolutely no role in quality per se. It is simply a resolution tag. The tag could be 72PPI or 180PPI but it doesn't have an inherent meaning, only what you could produce with the number of pixels you have at your disposal. Work with pixels! For example, let us say you have 1000x1000 pixels to keep the math simple. And to simplify this further, let's only consider the horizontal axis. If you have 1000 pixels and divide that by 72, that is, you provide 72 pixels per inch, you could end up with 13.8 inches using that division (1000/72=13.8). Let's now say you divide up your 1000 pixels using 180 instead. 1000/180=5.5. In both cases, you had 1000 total pixels. The document itself doesn't have a size, other than what space it takes up on your hard drive. The sizes above are examples of what could be produced if you divided up the total number of pixels you have, with some number of which is just a tag within the document. In Photoshop, if you use the Image Size dialog, turn resample OFF (do not allow it to create more or remove pixels), you can enter any value, 72, 180, 1000 into the resolution field and the resulting size is calculated for you. But you haven’t changed the document or the data at all. You just changed a theoretical 'size' if you output your 1000 pixels using that resolution. So again, it's meaningless until you output the data. At that point, lets say you print the image, you can decide how big you wish it to appear and/or how many pixels you want to devote to the output. You have 1000 pixels and someone tells you that you must use 300DPI (which isn't true but that's a different story). 1000/300 would produce a 3.3 inch print. You want a bigger print? Lower the DPI (within reason). You set the DPI for output to use 180 of your pixels to produce 180DPI? You get a 5.5 inch print (1000/180=5.5).

Work with pixels. That's a fixed attribute of the data unless of course you resample that data (add or remove pixels).

jrkliny
jrkliny Veteran Member • Posts: 4,092
Re: Contest requirements confusion: pixels vs. DPI

This is a common sort of specification for online submissions.  As mentioned above it is meaningless and whenever I see something like it, I just shake my head at what is often self perpetuating nonsense.  The only true specification is based on pixels.  Usually this is done to limit the number of pixels on the longest side.  Resolution is determined and adjusted by the device used to view or project the images.

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Philip Eihuyar
Philip Eihuyar Regular Member • Posts: 131
Re: Contest requirements confusion: pixels vs. DPI

SunfyreArt wrote:

Hi everyone!

I'd soon like to enter my first photo contest, but their requirements confuse me a bit:

They want a JPEG image, one side of which needs to be at least 4500 pixels, and its DPI needs to be 300. The winners' photos will be displayed either on a screen or printed at 50 cm x 75 cm or 100 cm x 150 cm.

I know it's possible to change a photo's DPI value without changing its size in pixels.

So, is that really all they want? A garden-variety 72 DPI, (for example) 6240x4160 pixel photo whose DPI has been changed to 300? Ô_o

Thank you!

I hope I can answer this actually not too complex question. The requirements of your image must be 4500 pixels of width per image and 300 dots per inch when printed. The dots per inch are refering to the printer's laying down of microscopic dots of ink of the printed image. The pixels width is for the width of the printed image for instance 13 inches wide or 17 inches wide.

If your image is of a smaller pixel count than required, you will just go into an image editing program and upsample the image to the required 4500 pixels width. Downsample if you have too many pixels. The image length will automatically be scaled to fit. Then, when you or they print the image in your or their printer to whatever size paper you choose, the requirements will be met.  Canon printers natively print at 300 dpi (Dots Per Inch) Since they specify 300 DPI, they probably have a Canon printer (Epsons printer natively print at slightly higher dots per inch -325 dpi I think) BTW, Pixels Per Inch is abbreviated as PPI. If you are printing from an Epson printer, just check with the the hosts of the contest. You should have no problem with these simple rules. Just remember DPI= dots per inch (printer) and PPI= Pixels per inch. Choose how large you want to print out your image and you are set.

edispics
edispics Veteran Member • Posts: 3,894
Re: Contest requirements confusion: pixels vs. DPI
2

Philip Eihuyar wrote:

SunfyreArt wrote:

Hi everyone!

I'd soon like to enter my first photo contest, but their requirements confuse me a bit:

They want a JPEG image, one side of which needs to be at least 4500 pixels, and its DPI needs to be 300. The winners' photos will be displayed either on a screen or printed at 50 cm x 75 cm or 100 cm x 150 cm.

I know it's possible to change a photo's DPI value without changing its size in pixels.

So, is that really all they want? A garden-variety 72 DPI, (for example) 6240x4160 pixel photo whose DPI has been changed to 300? Ô_o

Thank you!

I hope I can answer this actually not too complex question. The requirements of your image must be 4500 pixels of width per image and 300 dots per inch when printed. The dots per inch are refering to the printer's laying down of microscopic dots of ink of the printed image. The pixels width is for the width of the printed image for instance 13 inches wide or 17 inches wide.

If your image is of a smaller pixel count than required, you will just go into an image editing program and upsample the image to the required 4500 pixels width. Downsample if you have too many pixels.

Downscale? OP says AT LEAST 4500 which usually means 4500 or more, no downsampling required.

The image length will automatically be scaled to fit. Then, when you or they print the image in your or their printer to whatever size paper you choose, the requirements will be met.

What requirements. The only stated requirements are at least 4500 pixel width and an internal EXIF data element of 300 dpi in the submitted jpeg file.

OP clearly states he is asked to submit a file, not a print. OP clearly states that the contest organizers will print the winning photo in one of two sizes.

Canon printers natively print at 300 dpi (Dots Per Inch) Since they specify 300 DPI, they probably have a Canon printer (Epsons printer natively print at slightly higher dots per inch -325 dpi I think)

The target sizes specified by OP are 20 by 30 and 40 by 60 cm and there is no requirement for the submitter to upsample to the native print resolution at that target size. The requirement is simply to submit a file with a minimum width specified in pixels.

Native print resolution for Canon is 300/600 and 360/720 for Epson.

BTW, Pixels Per Inch is abbreviated as PPI. If you are printing from an Epson printer, just check with the the hosts of the contest.

OP clearly states that contest will print winners, contest is not requesting prints.

You should have no problem with these simple rules. Just remember DPI= dots per inch (printer) and PPI= Pixels per inch. Choose how large you want to print out your image and you are set.

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Philip Eihuyar
Philip Eihuyar Regular Member • Posts: 131
Re: Contest requirements confusion: pixels vs. DPI

Hi. My response was to explain what the terms, 'pixels per inch' and 'dots per inch' is in relation to what the requirements were to submit a file which as stated, might be viewed either in printed form or on a monitor. I responded because none of the previous posts addressed what the OP was not clear about. I hope I added to knowledge and not confusion for the OP.

Once the OP gets what those terms are, the specific requirements will make sense when the image file is sent.

David1961
David1961 Contributing Member • Posts: 874
Re: Contest requirements confusion: pixels vs. DPI

SunfyreArt wrote:

Hi everyone!

I'd soon like to enter my first photo contest, but their requirements confuse me a bit:

They want a JPEG image, one side of which needs to be at least 4500 pixels, and its DPI needs to be 300. The winners' photos will be displayed either on a screen or printed at 50 cm x 75 cm or 100 cm x 150 cm.

I know it's possible to change a photo's DPI value without changing its size in pixels.

So, is that really all they want? A garden-variety 72 DPI, (for example) 6240x4160 pixel photo whose DPI has been changed to 300? Ô_o

Thank you!

PPI is meaningless for screen display because a 600px x 1000px, for example, image will look exactly the same on a given screen whether its ppi is set to 72ppi, 300ppi or any other value.  PPI is used solely for sizing prints.

They say they might print the winner's image, but their min. pixel size and ppi requirement is less than their intended print size.  This doesn't make sense to me.

4500px/300ppi = 38.1cm.  Their stated min. print length/width is 50cm.

To meet the contest's requirements I would just do as they say and have one side at least 4500px and then using your image editing software set the image's resolution to 300ppi without resampling.

selected answer This post was selected as the answer by the original poster.
MrScary Veteran Member • Posts: 6,504
Re: Contest requirements confusion: pixels vs. DPI

Lets Keep it Simple shall we---If you use photoshop or whatever, if the ppi (pixels per inch) shows 72 or 96 from your camera just change it in the program to 300ppi. SIMPLES in it. Also stick to 300ppi for printing--Next, change your Tiff image size to whatever the comp are asking for. then change to JPG sRGB at 300ppi. Plenty on internet to show you if you Google it.

So, NO NEED to go pop eyed and go into reams of sentences to tell you everything. Why Complicate a simple answer to a simple question. Good Luck.

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jrkliny
jrkliny Veteran Member • Posts: 4,092
Re: Contest requirements confusion: pixels vs. DPI

MrScary wrote:

Lets Keep it Simple shall we---If you use photoshop or whatever, if the ppi (pixels per inch) shows 72 or 96 from your camera just change it in the program to 300ppi. ......

Even simpler, just ignore the any settings for dpi/ppi.  When the user looks at these images on a screen or uses a print program, those devices will automatically readjust the settings and whatever you submitted will be of no significance.  Those who ask for a specific setting just do not know what they are doing!

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David1961
David1961 Contributing Member • Posts: 874
Re: Contest requirements confusion: pixels vs. DPI

MrScary wrote:

Lets Keep it Simple shall we---If you use photoshop or whatever, if the ppi (pixels per inch) shows 72 or 96 from your camera just change it in the program to 300ppi. SIMPLES in it. Also stick to 300ppi for printing--Next, change your Tiff image size to whatever the comp are asking for. then change to JPG sRGB at 300ppi. Plenty on internet to show you if you Google it.

So, NO NEED to go pop eyed and go into reams of sentences to tell you everything. Why Complicate a simple answer to a simple question. Good Luck.

Thank you for essentially repeating the last paragraph in my previous post.

David1961
David1961 Contributing Member • Posts: 874
Re: Contest requirements confusion: pixels vs. DPI
3

jrkliny wrote:

...

Those who ask for a specific setting just do not know what they are doing!

That might be true, but the competition judges might disqualify the op's entry if they don't see 300ppi in the exif data.

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