Question for submitting photos

[Tintype_18]

I have a commission to write an article based on a presentation I gave at a writer's conference recently. I understand the requirements: 4x6 and jpeg format. Need some clarification on two things: required 2mb in resolution (how do I confirm this?), 300dpi (certain of this as dots per inch) but how to confirm this. Hope I have presented this clearly. If not, let me know. Thanks.

[rs-eos]

2 MB in resolution seems to be an odd way to phrase things, however, for a 4 x 6 image at 300dpi, that would be 1200 x 1800 pixels or 2.16 million pixels.

[FloridaDrafter]

I agree, Ricky. I think they, or John, means a 2mb cap on file size.

Newton

[Tintype_18]

Thanks. The 2mb is on their guidelines. Thought it was kind of odd, too.

[ebiggs1]

"...4x6 and jpeg format. ... required 2mb in resolution ..."

Neither 4x6 nor 2mb is a resolution spec. I suspect they want 4x6 photos and they have a limited amount of storage space so they put a 2mb file size limit. I would make my 4x6 photo look the best it can while watching the size limit.

Keep in mind DPI is a printer spec. Folks generally will discuss digital images in terms of DPI which seems to be OK or accepted at least the way things have gone. It is calculated by dividing the total number of pixels wide by the total number of inches wide. In your case you have a digital image that is 1200x1800 pixels and is 4x6 inches in
size.  Your photo has 300 DPI. Divide the number of pixels wide by the number of inches wide. Remember DPI is dots per inch. Whether this results in a 2mb file is not known.

[rs-eos]

Dots and pixels though can be used interchangeably in this context.  And since both physical size and DPI values are given, resolution can be obtained.

Equations become:

4 in x 300 pixels / in and 6 in x 300 pixels / in

The units of inch cancel and the final values (1200 and 1800) are now in pixels.

You're most likely correct that there's also a file size limit of 2 MB.  I know that Adobe Illustrator has in its export options the ability to constrain an image to particular dimensions while also capping the file size.  Other applications may also provide a preview/estimate of the resultant file size based on the JPEG quality setting.

[ebiggs1]

Perhaps this may clear it up a bit more. If you take the very same 4x6 inch photo at 300 DPI and blow it up to 8x12 inch, it now has a DPI of 150. But it is the very same image. Usually for nice looking prints you want to stay in that 150 to 300 DPI range. So, you see DPI is a relative term.

[ebiggs1]

Whether the two are interchangeable or not, technically they are not, software like Photoshop don’t help by confusing the situation including DPI in the Image size box. 

A big reason for all the confusion is how intertwined PPI and DPI are. A whole lot gets lost in translation when moving from screen to paper. Remember these facts. Pixels are not dots and DPI is not the same as PPI.

PPI is the number of pixels per linear inch of a digital monitor. This is the image’s resolution. 

DPI is a measure of the printer’s resolution. Every digital image has a set PPI, but an image doesn’t have a set DPI until it is sized for printing.

There are two ways to increase the size of an image, add more pixels or make the pixels themselves larger. Also, you can reduce an image’s size by shaving off pixels or shrinking pixels. Shrinking and shaving are two different abilities. Resizing an image changes the actual size of its pixels, but not the number of pixels. Resampling changes the image’s size, larger or smaller, by increasing or decreasing its total number of pixels. Photoshop’s Image Size box controls both resizing and resampling.

If you make an image in PS that is 600 pixels wide and 400 pixels high and set the DPI to 72, it is 240,000 pixels. Make another image also 600x400 but at 300 DPI. It is still 240,000 pixels. Because 600x400 remains 240,000 pixels. The DPI doesn’t make a difference because we are not printing the image.

[Tintype_18]

I'm was just passing along what the photography guidelines included. That is why I made this thread to get feedback from the forum members. I'm going to finalize the text today or tomorrow and work on what photos I have. Again thanks to all.

[ebiggs1]

Any place or organization that is photography literate at all will not ask for images by DPI. At least they should not!