photoshop newbie question regarding image sizing and pixelation

[crny1]

Hello all,
Pardon the ignorance as I am watching videos and trying to learn PS but its a long process. I have a question regarding a file I am working on. I have a jpg from shutterstock that I have downloaded. The photo is 5632 x 3756 px18.8" x 12.5" (300dpi) when I download it. Using image size in PS I brought the image up to the size I needed. 60" tall and width proportionate. PS resamples it automatically to make this size. Now the picture still looks good in PS. I save the file and now place it onto a artboard in illustrator where I need it and it looks pixelated. Why is this? The whole DPI, resolution and all that has me lost at the moment and I am trying to wrap my head around it but, I think I need someone to help explain it in laymen s terms or something. Can anyone help out by shedding some light before my head explodes? Thanks

 

[Correct Color]

Well, just to start, a digital image is never measured correctly in dots per inch. So to be correct, at its initial size, it was 300 ppi (pixels per inch) not dpi (dots per inch.)

What's the difference? A pixel is the smallest unit of complete color information in a photographic/digital image. A dot is the smallest unit of individual colorant in a printed image. They are not interchangeable terms.

So then, your image is made up out of pixels, and basically if you divide 5632 by 18.8 you get 300. Which gives you 300 pixels per inch, your original image. It works on the other dimension as well.

If you size the image up to 60 inches, you can do the math again: 5632 divided now by 60, and you get 94 pixels per inch. And that's actually usually at the lower end of okay for just about anything you're likely to be doing in large format printing that isn't fine art. In fact, I'd say your image shouldn't look pixelated in Illustrator. That might take a bit more investigation to solve, but this is how the process basically works.

 

[bob]

Most simple resizing upwards of bitmaps such as you describe usually results in some combination of larger and/or duplicated pixels giving the resultant image that dreaded 'pixelated' look. For example if you were to re-sample a 3"x3" bitmap OF ANY RESOLUTION to 6"x6" what you'd likely end up with is each pixel being replicated 3 times thus, for each original pixel, 4 identical pixels would be generated.

Bitmaps are best enlarged with some sort of spline fit algorithm. These will upsize a bitmap with absolutely no pixelization whatsoever. There are other less dramatic secondary effects such as pixel bloom but these are relatively trivial as compared with giant pixels.

The number of proprietary packages out there are legion. I use PhotoZoomPro, which is built into Corel, but any of them will do the job and none of them will make silk purse out of a sow's ear. You have to have a reasonably good image with wich to start.

 

[oksigns]

Hello all,
Pardon the ignorance as I am watching videos and trying to learn PS but its a long process. I have a question regarding a file I am working on. I have a jpg from shutterstock that I have downloaded. The photo is 5632 x 3756 px18.8" x 12.5" (300dpi) when I download it. Using image size in PS I brought the image up to the size I needed. 60" tall and width proportionate. PS resamples it automatically to make this size. Now the picture still looks good in PS. I save the file and now place it onto a artboard in illustrator where I need it and it looks pixelated. Why is this? The whole DPI, resolution and all that has me lost at the moment and I am trying to wrap my head around it but, I think I need someone to help explain it in laymen s terms or something. Can anyone help out by shedding some light before my head explodes? Thanks

I assure you that resized image you have is not 300dpi

An image can become so large that it needs to be saved as a PSB file, otherwise, Photoshop will suggest you save it under a different resolution or smaller dimension.

 

[Fred Weiss]

When dealing with image sizes, the only thing that matters is pixel dimensions. That shows you the actual size of the image so you can evaluate its suitability for your project. Resolution, DPI etc. only come into play when you hit the Print button.

In the following examples, it should be clear how these things can be evaluated. I have created an image in Photoshop that has pixel dimensions of 3,000 x 3,000. If I click on the Image menu > Image Size, the dialog shows me the various numbers. If I uncheck the "Resample Image" check box, I see that the size is 41.667" x 41.667" at a resolution of 72 pixels per inch. If I change the Resolution setting to 100, then the size will be 30" x 30". And if I change the Resolution to 300 PPI, the size drops to 10" x 10".







These changes do not represent any change to the actual image because Resample is unchecked. They simply show you what you have to work with. When you turn resampling back on, any change you make will result in a physical upsizing or downsizing to the image which is where pixelation and other distortions will happen. So if the actual print size needed is 30" x 30", I know that I can print it at a resolution of 100 PPI without resizing it. But if I need to print it at 300 PPI and at 24" x 24", then I will need to enlarge it to 240% of its original size unless my experience tells me that the RIP software and other print settings will produce a satisfactory print without modifying the original image.

Digital imaging, editing, processing and printing is a science ... but it is also an art and a craft. You'll get better with time, practice, experimentation and experience.

 

[peavey123]

If you brought the image into photoshop to only scale, not to edit the image in any other way then you should have just skipped photoshop and scaled the image in illustrator as you didn't change anything by re-sampling the image in photoshop.

So your 5632 x 3756px or 18.8" x 12.5" (300ppi) image scaled up to 60 inches tall would be 62.5ppi. or that 60in tall re-sampled image would also actually be 62.5ppi even though it's saying 300ppi because you resampled it. The re-sampling function cannot add pixels to your image, it more just allows you to reduce resolution when scaling images so you don't end up with an image that is 6"x6" at 2400ppi when you only need it to be 300ppi.

 

[crny1]

Sorry for the delay in responding.
OKSIGNS, sorry if I made it sound like I thought the resampled image was 300 ppi. I knew it was no longer that ppi.

Correctcolor and Fredweiss, Thanks for the math lesson. This helped me to understand more of the process.

bob, I have photozoom pro but my file sizes are HUGE when creating the new resized image and the result usually is a bogged down illustrator due to the large files. This image needed more than resizing in PS is why I opted for that method. I have been told on numerous occasions to skip photozoom and just do it with PS. Maybe its something I am doing with either photozoom or the PS side of it......

Thanks for the info so far. Its starting to make some sense. Unfortunately today life got in the way and I was not able to work with PS more and watch more videos.

 

[jfiscus]

Illustrator/InDesign's on-screen previewing capabilities are not the best, so you can't trust "how stuff looks" in them. You have to know or trust your original image's quality and whether or not is going to work at the intended size; 100+dpi is plenty fine for large format.

Your image sounds like it is good enough quality for what you're intended use is. If you need to enlarge an image I recommend using OnOne's enlargement software.