Crop Resolution in .jpg or .tif

[Kov-Ice]

I take photos with a 5MP camera. They're saved as .jpg files, but with a giant size (like 22" x 16"). I believe their native resolution in 72 dpi.

When cropping in Corel PhotoPaint, I'm given the option of changing the resolution when I change the size. I'm printing these pics out as 8x10s, 5x7s, and 3.5x5s for framing purposes, so I want the best clarity. Do I leave the cropped res at 72? Would increasing the resolution to 150 or 300 make the picture better, or wouldn't it actually increase the pixelation of the image? Thx.

[mairving]

As a general rule, use 300dpi for printing (or the highest res available). If you put them on a website, then you would use 72dpi.

[Kov-Ice]

But if they were taken with 72 dpi resolution and I increase that, won't that extrapolate to add pixels to the image? I'm thinking that might cause the photo print to turn out poorly or pixelated. I don't really know, but I sure want to check before I pay to have this bunch of pictures finished.

[Kov-Ice]

Any other additions? I know when scanning/printing, the higher res the better. But when cropping and saving to a new file, what's the better way to go with the res (lower, same, or higher)? I'd like to get these photos to the camera shop tonight if I can. Thanks.

[Force Flow]

It's when you decrease your dpi that your picture gets pixelated. Increasing it allows you to look at it closer (or zoom in more) without appearing pixelized.

For the web, it's usually 72; for general and small pics 150; for higest quality and large pics 300.

[Kov-Ice]

I guess my confusion stems from the Corel PhotoPaint manual. It says:

You can change the res using two methods - upsampling and downsampling. Upsampling increases res by adding more pixels per unit of measure. Downsampling removes pixels per unit of measure. Because upsampling adds pixels, it can reduce the quality of an image. Downsampling produces better results than upsampling.

Hence my confusion. Seems backwards to me as well, but I don't understand what's up...

[Force Flow]

Upsampling makes the pic appear almost "blurry".

[TwoRails]

Changing DPI is just a setting and does not change the photo or resample. Just don't change the actual photo size, just the print size, or the DPI setting. If you change just the print size / DPI, the photo doesn't get resampled.

HTH

TwoRails

[Kov-Ice]

OK, I found out that if I check Maintain Original Size, then changing the dpi actually constrains (that the right term?) the image by adding pixels proportionally to the amt the photo size is reduced. Like my large size photos are
2560 / 72 pixels = 35.55 inches (when printed)
1920 / 72 pixels = 26.66 inches
Then with that checked, increasing pixels makes
2560 / 300 pixels = 8.5 inches
1920 / 300 pixels = 6.4 inches
Still not sure I'm grasping it or understanding why that's called Maintain Orig Size, but makes a bit more sense, I guess.

My original concern was that in cropping, should I leave the cropped dpi (that's an option I'm given each time) at that same 72 dpi, and I guess that's so. Even tho cropped, the smaller photo (and file size) still has the same res, right? And increasing the dpi when cropping would be upsampling, wouldn't it?

Still learnin' here...
Kov

[TwoRails]

Hopefully, this will help. It seems like you are interchanging things that maybe you shouldn’t, like image size and print size. Image size is the physical size of the photo and therefore is also directly related to the file size on disc and is basically changed by resampling. So, if you wanted to change a photo from 1280x768 to a 800x600, then the physical size is changed and therefore it will be resampled. The DPI remains the same which means that the print size would also be reduced.

“Maintain Original size” normally refers to the Print size. So, if the 1280x768 had a DPI so it would print as 8x10, then the DPI would also change when you reduced the physical size down to 800x600, making the print size remain at 8x10. (These are factious print size numbers for simplicity in the example.)

So, if you want to change the Print size, just change the DPI, Not the physical size of the photo. Keep the pixel size the same and the physical size will remain the same.

In your examples below, it seems like you are missing information. The first number appears to be one half of the photo size, the second number should be the DPI, and the final number is one half of the print size. So the 1920 / 300 part should be 1920x1200 pixels by 300 DPI equals 6.4x8.5 Inches print size. (or are you breaking up one line of info into two lines??)

BUT, it’s all a moot point if you are printing from within your graphics editor program; most (if not all) programs let you change the print size from the print preview window. This does not change the file, and all settings are done for you.

Also, there is two basic ways of cropping. Since digital film is not the same aspect ratio as film film, a digital photo will not fit exactly in film print sizes (unless your camera has a special setting for this). So, if you “crop” using the “fit to” size of 8x10, then all your doing is cutting of the edges of the digital film so it will properly fit into the standard of 8x10. It doesn’t change the DPI and changes only very slightly the physical size (as you are removing part of the photo).

I made several examples for you so you can visually see what I’m talking about.

They will follow after this post.

HTH

TwoRails

Originally posted by Kov-Ice 2560 / 72 pixels = 35.55 inches (when printed) 1920 / 72 pixels = 26.66 inches 2560 / 300 pixels = 8.5 inches 1920 / 300 pixels = 6.4 inches

[TwoRails]

Here is the description of the following examples:

Example 1 is a simple square photo with a round colored area inside. The size is 300x300 pixels with a DPI of 72.

Example 2 is the very same pic, with the only thing changed is the DPI, which is now set to 300 DPI.

The important thing to note is the file (physical) size is the same as nothing changed but the DPI setting.

Example 3 is a screen shot of my Print Preview area, showing that, even though both pics are 300x300 pixels, and are the same physical size, they will print differently.

(Note that you can change the print size in this window without changing the original... making printing photos of different sizes quick and simple)

TwoRails.

Example 1 is attached:

[TwoRails]

Here is Example 2, which is the very same pic as Example 1, but with a DPI of 300 instead of 72: (note that is appears the same size on a computer screen, as computers show pics at a DPI of 72)

[TwoRails]

And here is the screen shot of the ration between the actual print sizes: (the white background represents the standard 8.5x11 inch piece of paper)

PS: also, the little ball on top is the one set to 300 DPI, and the larger, lower one is at 72 DPI.

[Kov-Ice]

Hey Rails, thanks for reply. Before posting this thread, I actuall found another one in which you had some pretty in-depth descriptions of this stuff.

Originally posted by TwoRails It seems like you are missing information. (are you breaking up one line of info into two lines??)

Ya, in my examples I split the horizontal and vertical into two different lines for ease of calculation.

Your top example on the Print Screen =
300x300 pixels/300 dpi = 1 inch x 1 inch

bottom example =
300x300/72 dpi = 4.17 inches

Is that about right? The file size stays the same because the actual image size is packed with more info (pixels) and therefore stays the same on disc. The physical print size changes because you can only print so many pixels per inch. That close to correct?

Originally posted by TwoRails “Maintain Original size” normally refers to the Print size.

That's what I would've thought, but on Corel's Photo-Paint it apparently refers to Maintaining the Original File Size. When I resample images, checking 'Maintain Original Size,' it increase the DPI of the image, while reducing the physical dimensions of the photo when printed as described above. At any rate, I think I have a little better idea of what I'm doing and why it is so. Thanks again!

[TwoRails]

Originally posted by Kov-Ice Your top example on the Print Screen = 300x300 pixels/300 dpi = 1 inch x 1 inch bottom example = 300x300/72 dpi = 4.17 inches Is that about right?

Sound good to me

The file size stays the same because the actual image size is packed with more info (pixels) and therefore stays the same on disc. The physical print size changes because you can only print so many pixels per inch. That close to correct?

Pretty close. The DPI is just an instruction on how to print the photo. So, if you change just that, you are not really changing the photo data inside the file, just part of the heading. The data size doesn't change, therefore the file size is the same.

Sounds like your getting a good handle on things!

Have fun play around with all of it

TwoRails