8 Replies Latest reply on Feb 9, 2013 7:50 AM by JJMack

# True Resolution for Image

Hi, as I search the internet for a particular popular image, when it pops up in Google image search, it shows up with a bunch of different resolutions / sizes / whatever you call it. I assume that when the image was originally created, it had one resolution it was created it, the one where it's the best quality. Is there a way in photoshop to figure this out? ie what is the optimal resolution that an image should be displayed at?

For instance, I'm doing an image search on "success kid" which is a popular meme. Of all the images that pop up, should I take the one with the highest resolution? But however could that have meant that it was resized to be very big?

Just a little confused about resolution in general.

• ###### 1. Re: True Resolution for Image

One can only make assumptions that the biggest is the original.  So take the biggest image they have and you can always downsize.  You can not add deail if resolution is too low.

• ###### 2. Re: True Resolution for Image

A digital image (on the web, or on your computer) doesn't have a resolution, it has only a pixel dimension. For instance you see 3000 x 2000 pixels. That is the pixel dimension.

The pixel dimension is so many pixels wide x so many pixels tall. There is no resolution involved, and it doesn't make sense to speak of resolution.

Resolution (pixels per inch =ppi or dots per inch =dpi) comes into the play when you print an image. To get a quality print we need a certain amount of dots per inch (dpi) on the paper - let's say 300 dpi.

So when you have an image with a pixel dimension of - let's say - 3000 x 2000 pixels, and you want to make a print with 300 dpi, your print will be 10" x 6.66" (Divide pixel dimension by wanted resolution).

Now, if you wanted to print this image in a size of 30" x 20", you would have only 100 dpi and the image would not look good: the resolution of 100 dpi is too low. But you can "upsample" the image in Photoshop, that means that Photoshop "invents" new pixel to fill in the missing ones so that you arrive at a higher resolution for the print.

Resolution is not something inherent to an image, it is something the we select for the print.

Monitor screens of today have often have a resolution of about 100 ppi (the CRT monitors of old had 72 ppi). No matter what the pixel dimension of an image is, the monitor will display it with 100 ppi.

So the image of 3000 x 2000 pixels will be (approximately) 30" x 20" on your screen, i.e. it is way to large, and you would see only parts of it. (Modern browser automatically resize the image, so that it will be displayed in full). And if the same image has been downsampled to a pixel dimension of 300 x 200 pixels, it will be displayed on screen with a size of (approximately) 3" x 2".

There is no way of telling which of the sizes you see for an image is the original one. Because the image has most probably been resized, and none of the sizes shown might be the original.

In Photoshop you can downsample an image (make it a smaller pixel dimension) or you can upsample an image (make it a larger pixel dimension). You can do that in other photo editing programs as well. We don't know what happened to the image before it got posted.

You ask: "Of all the images that pop up, should I take the one with the highest resolution?"

That depends on what you want to do with it. Just display it on your screen? Print it, and in what size? Put it on your website? Send it by e-mail?

For each of these purposes a different pixel dimension would be ideal. For instance: The largest size would not be ideal for e-mail. It takes a long time to send and to receive the e-mail.

• ###### 3. Re: True Resolution for Image

Thanks for that long reply. I have an iPhone / iPad app which imports these images and the user can resize them with their finger. I want them to maintain high quality for any size they get resized to. Maybe resolution is the wrong word, but it's the pixel dimension or whatever, where if you go bigger than that size, then the picture starts to become pixelated and look bad. I'm trying to figure that out, how big can I make this picture before it looks bad. I thought that was resolution but I guess I was incorrect.

• ###### 4. Re: True Resolution for Image

I thought that was resolution but I guess I was incorrect.

No, you were using it correctly. The problem is the same term has come to define different things. I agree with web-weaver that pixel dimension and PPI are very different concepts. Where I disagree is that I think the term "resolution" is more appropriate for pixel dimension whereas PPI would be better described as "pixel size" or "pixel density".

Regardless, yes, look for images that have the largest pixel dimensions.

from my friend Merriam:

resolution: a measure of the sharpness of an image or of the fineness with which a device (as a video display, printer, or scanner) can produce or record such an image usually expressed as the total number or density of pixels in the image

total number = pixel dimension

density = PPI

and those two things are different beasts. So you can see the problem with the term "resolution".

I want them to maintain high quality for any size they get resized to.

Ain't no such animal. At a certain point any pixel based image can be enlarged enough to look pixelated.

• ###### 5. Re: True Resolution for Image

Yes PPI is pixel size.  If you have an image x pixel wide and y pixels high you can display that image any size you want. If you use very large pixels like 1 PPI you will see a large boxy image you will see every square pixel.  If you use 1/100" size pixels 100 DPI you may see large soft image. If you use 300DPI pixels the image will be smaller and sharper. If you use 3000DPI size pixels you may only see a dot on the paper.

All pixels do not have the same quality. Some may be very high in quality and other much lower in quality.  Was a good lens used was it focus well was the sensor good was the light good was high ISO used there more to it the just the number and size of pixels.

• ###### 6. Re: True Resolution for Image

Resolution is usually defined as pixels per inch (ppi) or dots per inch (dpi).

This "per inch" brings in a length measurement that makes sense only for prints.

You said "the term "resolution" is more appropriate for pixel dimension".

Well, you have the right to define words in any way you wish. But I think to equate resolution with pixel dimension is not helpful and does not clarify the issue.

Pixel dimension is just the number for the pixels that the image has along its long side and short side.

When we talk of resolution we always say "per inch" or "per centimeter".

Look at how Photoshop defines resolution in >Image >Image Size, see screen shot.

What you see for <Width> and <Height> at the top of the dialog box that is the pixel dimension. And it says so in the header.

Now do a test: Uncheck the box <Resample Image>, and change the Width and Height in inches (Pixel dimension becomes un-editable). Change the Width to a much larger value and see what happens to your resolution. It goes down. But the pixel dimension remains unchanged.

But when the box <Resample Image> is checked, and you increase the Width in inches, the resolution remains the same but the Pixel Dimension goes up.

• ###### 7. Re: True Resolution for Image

Well, you have the right to define words in any way you wish.

No, I don't. (see above Merriam Webster definition)

Resolution describes the detail an image holds. In MLTHO that concept is more accurately described by number of pixels, not size of pixels. The only thing image  PPI indicates is how big pixels will print IF OR WHEN an image is ever printed. Period.

Image PPI describes printed pixel SIZE.

when people talk about "high res" or "low res" images...  99% of the time they are talking about pixel dimension (i.e., total number of pixels)

As you well point out, the Photoshop Image Size dialog contributes to this confusion.

• ###### 8. Re: True Resolution for Image

Well, you have the right to define words in any way you wish.

No, I don't. (see above Merriam Webster definition)

Resolution describes the detail an image holds. In MLTHO that concept is more accurately described by number of pixels, not size of pixels. The only thing image  PPI indicates is how big pixels will print IF OR WHEN an image is ever printed. Period.

Image PPI describes printed pixel SIZE.

when people talk about "high res" or "low res" images...  99% of the time they are talking about pixel dimension (i.e., total number of pixels)

As you well point out, the Photoshop Image Size dialog contributes to this confusion.

There is more to it then number of pixels. You can have billions of pixels if the lens use was not in focus you have no details you have a blur.  PPI is pixel size while different size UXGA displays all display 1600x1200 pixels each display size has a single PPI resolution.  My 20" UXGA  PPI resolution is 100PPI my  15" UXGA PPI resolution is 133PPI the same 1600x1200 image displayed on both is sharper and smaller on the 15" display then on the 20" display. 12"x9" on the 15" display 16"x12" on the 20" display.  Printers can print different size pixels they are not confined to a single pixel size like displays so my Epson 4800 could print both the 12"x9" 133DPI image and the 16"x12" 100ppi image.  PPI is pixel density it applies to displays sensors any device the displays or captures pixels. Resolution is also measured in resolving power how well a lens can focus a point or something like that.  Displaying an image at different sizes on a display is done by scaling the number of pixels used to display the image with the display's single pixel size.

Photoshop Image Size Dialog supports two types of resizing controlled by the RESAMPLE check box.

With RESAMPLE Un-check you will see that the dialog top area is grayed out and can not be changed.  The number of Pixels can not be changed and the Images Aspect Ratio can cot be changed. You will see that the Width, Height and Resolution are linked together in the middle print size area all you need do is to change one of these and Photoshop will calculate the other two.  When RESAMPLE is un-checked the other controls in the bottom section are not relevant.

With RESAMPLE CHECKED the current Document Image will be replaced with a new generated image not a single pixel will remain intact.  The number of pixel in the new imaged depend on the other setting used. The bottom section setting controls the resize operation. Interpolation how the new pixels are generated. Constrain when checked links the Documents Width and Height the Documents Aspect Ratio will not change and the image will not be distorted into a new aspect ratio. Scale Styles may or may not be grayed out. Layer Styles have absolute pixels settings not relative settings if you change the number of Pixels in an image layer style may look quite different if you do not have Photoshop scale the styles setting during an Image Size resize.  With RESAMPLE CHECK it best to also check Constrain to prevent distortion.  If you resizing for the web set the width or height in the top section that you want. Resizing for print first with RESAMPLE UN_CHECKED set the print width or height that you want. If the resolution falls below the resolution you need for printing CHECK RESAMPLE and set in the RESOLUTION you want the image printed at and set the interpolation method you wan used.

Printing:  Your Printer resolution setting is a print quality setting. As long as you image DPI resolution is lower then the Printer's resolution setting all is fine.  Printers use their higher resolution capabilities to paint in you image larger pixels. It like paint by the numbers fill an image pixel with drops of different color inks to produce the correctly colored pixel. There is no one to one correlation.