Save 300 dpi jpegs

Question

I have a tiff file of a painting I scanned at 300 dpi. It's original image size when I open it is photoshop is 57.8 MB, 18" W by 12.477" H, Res 300. I need to resize it and send it as a 300 dpi jpeg. I have started in the image size dialogue box and just change the W to 11.25. That automatically changes the H to 7.798 and the res still says 300. The file size reduces to 22.6 MB. I click ok and then go to save as and choose jpeg. In the jpeg box I chose 12 Max and baseline standard and click ok. The saved file is reduced to 8.5 MB. When I open it in photoshop, it opens at 300 dpi when I look in the image size box. However, when I send it to someone else and they open it, the file is only 72 dpi. What am I missing to get the file to save at 11.25 inches, jpeg, but remain 300 dpi?
Thank you.
Sheilaartist

Answer 1

I have a tiff file of a painting I scanned at 300 dpi. It's original image size when I open it is photoshop is 57.8 MB, 18" W by 12.477" H, Res 300.
That means you image is 18x300=5400px wide and 12.477x300=3743px high  widthxheight=numbed of pixel 3 bytes per pixel for 8bit color 5400x3743x3=60,636,600 which is close to Photoshop 57.8MB estimate or the Tiff file is 57,8MB.
I need to resize it and send it as a 300 dpi jpeg.
Then all you have to do is resize the open document and save a jpeg file.
I have started in the image size dialogue box and just change the W to 11.25. That automatically changes the H to 7.798 and the res still says 300.
That means you also have RESAMPLE and Constrain checked in the Image Size dialog bottom control section and some interpolation method is set. Photoshop will reduce the number of pixels you have for the image. When you click on OK Photoshop will generate a new image that is  11.25x300=3375px wide and 7.798x300=2339px high
The file size reduces to 22.6 MB.
The file is not changed when you use Image Size.  The Tiff file remains as it was before it was opened. Photoshop is a document editor not a file editor.
I click ok and then go to save as and choose jpeg.
When you use "Save as" and use the pull-down menu and select Jpeg you will be saving a new file and not be over writing the tiff file.
In the jpeg box I chose 12 Max
That is a quality setting the higher the number (Max 12) the better the file quality will be the file will be less compressed then when lower quality setting are used.  You would be hard pressed to see any image quality difference between quality 10 file and quality 12 file.  The quality 10 file size will be quite a bit smaller then a quality 12 jpeg file.
and baseline standard and click ok. The saved file is reduced to 8.5 MB.
The new jpeg file size is a product of the jpeg quality setting and how well the image data compresses.  Size can vary all over the place.  Images with lots of fine details will be larger then images with little detail.  An image of a white wall will compress much smaller the an image with the same number of pixels that has a lot of details like an image of a cross word puzzle.
When I open it in photoshop, it opens at 300 dpi when I look in the image size box.
Correct you did not change the resolution when you resampled the image.
However, when I send it to someone else and they open it, the file is only 72 dpi. What am I missing to get the file to save at 11.25 inches, jpeg, but remain 300 dpi?
If when they open the file the receive they see an  image that has a 72dpi resolution. It means either what you used to send the file resized the the image and sent a different file or what was used to receive the file resized the image and saved a different file. Or the image was resized by the image processor the user used to open the file either during open or after it was opened.  For example if the user received the file you saved and sent 3375px wide and 2339px high and 300DPI and opened it in Photoshop and Photoshop is set to open Jpeg images through ARC the users ACR default workflow setting could be set to open image at 72DPI.  An image dpi is a setting the image may still be 3375px wide and 2339px high however set to 72 DPI the print size would be 3375px/72=46.875"  wide and 2339px/72=32.486" high  using Image size changing itr 72dpi print resolution to 300dpi with RESAMPLE NOT CHECK would return it size to 11.25" x 7.798" at 300DPI.