pixel dimension

GG
Posted By
Glaucio Garcia
Nov 25, 2003
Views
658
Replies
11
Status
Closed
Hi there,
I have a set of hi resoltion images files with pixel dimension mixed, and now, I have to convert to a set of images files with exactly pixel dimension = 3MB. How can I do it?
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L
larry
Nov 25, 2003
The quickest way would be to use the Crop Tool. Input your desired pixels per inch (resolution) and your desired pixel dimensions. Then drag diagonally across the images.

Larry Berman
GG
Glaucio Garcia
Nov 26, 2003
Hi Larry,

Thanks for your tip, but it did not help me. I have tryed to drag diagonally across the images, but I can not select the total area of image. Do you have other idea?

Glaucio Garcia.
GH
Gernot_Hoffmann
Nov 26, 2003
Glaucio,

if dragging across the the diagonal doesn´t show the total pixel number then it can´t be avoided to apply some simple calculations (go to formula in dotted lines …).

For the moment I´’m assuming that you don´t want to crop. Then the aspect ratio will be retained and we have to calculate the scale factor.

newX = Scale*oldX
newY = Scale*oldY

newSize = newX * newY * 3byte = 3 MB

Scale^2 * oldX * oldY = 1Mill

Scale = Squareroot ( 1Mill / (oldX*oldY )

Can be simplified:
————————————————–
newX = 1000*Squareroot(oldX/oldY)
and use old aspect ratio
————————————————–

1. Example:
oldX=1500, oldY=1000
newX = 1000*Sqrt(1.5) = 1252
and as a check
newY = 1252/1.5 = 815
Size=3*1252*815 =2.995 MB

2. Example:
oldX=4000, oldY=4000
newX=1000

Best regards –Gernot Hoffmann
GG
Glaucio Garcia
Nov 27, 2003
Gernot,
I did´t get your tip. I´ll explain my problem again:
I have thousends of images in different sizes. And I need all of them to have 3MBsize (aprox. 11 x 17 inches / 72 dpi – without loosing any information – that´s why the crop is not worthy).
Is it possible to use the Photoshop 7 to automate this work, so that I can leave Photoshop doing it for me (ex.: opening the images and "resizing" it alone)?
If it is possible, can you explain me it step by step?
Thank you.
Best Regards,
Glaucio
L
larry
Nov 27, 2003
Create a batch operation by resizing to 72 pixels per inch and Fit Image to 17×17 inches. That will resize everything to fit so the long dimension is no greater than 17 inches. Then add canvas to all the images filling out the other dimension. Your resulting files will be exactly 11×17 at 72 pixels per inch.

Larry Berman
GH
Gernot_Hoffmann
Nov 27, 2003
Yes – this is much simpler, but based on the assumption that the source images have also the aspect ratio 11:17 (approximately, a tolerance of +-10% is probably allowed).

I thought that the source images could have any arbitrary aspect ratio. If a source image has the aspect ratio 1:1 then the file will become larger than 1Mill pixels = 3MB .

Best regards –Gernot Hoffmann
L
larry
Nov 27, 2003
You can’t have it both ways. Either the images will be the same physical size (pixel dimensions) or the same weight (megabytes). I’d go for a uniform size. Dropping into a 17×17 Fit Image will retain the proportions of the individual pictures, adding the canvas will make them close to a uniform megabyte size.

It’s difficult answering as we don’t know what the purpose of the resize action is. How are the images to be used?

Larry Berman
S
surena
Sep 30, 2005
forgive me for this elementary question.
What is the number in image size/pixel dimension stands for?For example I have a picture in JPG format with pixel dimension of 800*536, resolution 72 pixel/inch. The size of it is 346 kilobytes. In front of pixel dimension and also in status bar the number 1.23M is written. What is this number?

Surena.
P
PiT
Sep 30, 2005
hi surena,

jpg is a compressed fileformat (like e.g. *.zip). the filesize info in status bar shows the amount of working space (ram) during working on image. the resolution of 72 dpi (almost produced with digicams) targets to an output on screen – an output to a desktop printer requires a minimum of roundabout 200 dpi.

—
PiT

"surena" schrieb im Newsbeitrag
forgive me for this elementary question.
What is the number in image size/pixel dimension stands for?For example I have a picture in JPG format with pixel dimension of 800*536, resolution 72 pixel/inch. The size of it is 346 kilobytes. In front of pixel dimension and also in status bar the number 1.23M is written. What is this number?

Surena.

T
Tacit
Sep 30, 2005
In article ,
"surena" wrote:

What is the number in image size/pixel dimension stands for?For example I have a picture in JPG format with pixel dimension of 800*536, resolution 72 pixel/inch. The size of it is 346 kilobytes. In front of pixel dimension and also in status bar the number 1.23M is written. What is this number?

Your picture is 800 pixels wide and 536 pixels high. Each pixel is a square of color that is 1/72 of an inch wide. The picture is 1.23 megabytes in size.

The JPEG file format is compressed. Your picture is 1.23 MB in size, but when it is compressed, it takes up 346 kilobytes of disk space.

JPEG compression is "lossy." The file is made smaller on disk because image detail is deliberately and permanently thrown away, and the quality of the image is degraded. This is why you should never save a file as JPEG unless you have some specific reason why it has to be JPEG and no other file format will work; JPEG was intended for situations where file size is critical and image quality is not important, such as for the Web.

—
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FJ
Frank Jones
Oct 27, 2005
On Fri, 30 Sep 2005 15:05:43 GMT, tacit wrote:

In article ,
"surena" wrote:

What is the number in image size/pixel dimension stands for?For example I have a picture in JPG format with pixel dimension of 800*536, resolution 72 pixel/inch. The size of it is 346 kilobytes. In front of pixel dimension and also in status bar the number 1.23M is written. What is this number?

800 x 536 = 428800 pixels

24 bit colour = 3 bytes (R, G and B) per pixel = 1,286,400 bytes

1 megabyte = 1024*1024 bytes = 1,048,576 bytes

1,286,400 / 1,048,576 = 1.2268 megabytes, say 1.23M.

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