Pixel Dimention

[akmu]

What is the difference between pixel dimentions and document size.

Once I know document size I should know pixel dimention.

  Just for a test I have done document size.  I saw certain small size.  Then when I changed pixel dimention in the same output was bigger.   How come?  I have to change pixel dimention also always? 

[John T Smith]

Please post the name of the program you use so a Moderator may move this message to that forum

[akmu]

Name of the program photoshop CS3

[Peru Bob]

Moved to the Photoshop forum.

[JJMack]

Pixel have no dimensions till you specify the document print ppi resolution.  PPI is pixel density in other words Pixel Size 300PPI means 1" contains 300x300 pixels That is 90,000 pixels that are 1/300" by 1/300" each.

An Image has Pixels X pixels wide by  Y pixels the number of  pixels your image canvas.    Pixels data is the bulk of images file sizes. 

When you set the Print resolution you can calculate the size the image will print.

X Pixel/ppi by Y Pixels/ppi

That data is compressed in the files there is no direct correlation between Files size and Canvas size when compression is used.  How well an image will compresses depends on Image content not canvas size.

When Compression is not used images that have the same canvas size. Their file sizes will be very close. Files will contain the same amount of Pixel data the amount of meta-data may vary between images.

[akmu]

Still I did not get th differece between document size and ppi dimension please. 

[D Fosse]

A Photoshop file consists of pixels, that's all. There's nothing more. So many pixels wide by so many pixels high.

The file has no physical size, as in a print size. That's arbitrary and you can spread the pixels out as thinly as you want to produce a bigger print at lower density (pixels per inch). Ppi is not a property of the file.

File size on disk is determined by whether the file format applies compression or not, and how effective that compression is. A file format is a storage format, when the file is open it is decompressed and unpacked and doesn't have a file format at all.

[JJMack]

PPI is Print pixels size. ie 300ppi  pixels size is 1/300 Inch by 1/300 Inch

Document size is the canvas  size  X pixels wide by Y pixel high some number of Pixels like  like X time Y may be 8MP

The document canvas has no physical size till you print the pixels.  And How big the print will be depends on  the Pixel size used  to print the image the print  PPI resolution.

My 8.2MP Canon Image

[NB, colourmanagement net]

Hi

A Photoshop file has a number of pixels, X pixels by X pixels 

It's print or display size is determined by how those pixels are used, that’s what PPI means, "Pixels Per Inch.

How many of the file's pixels will be used to to fill an inch when printed. 

Best not to "invent" pixels in resizing, if you can avoid it. To set print size decide how manu pixels are needed per inch (maybe 240 - 300) and see how it sizes up compares to what printed size you need.

For images online (websites) size is only expressed as pixles. Then the HTML sets the displayed size. 

I hope this helps

if so, please "like" my reply and if you're OK now, please mark it as "correct", so that others who have similar issues can see the solution

thanks

neil barstow, colourmanagement.net

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