Summary of steps:

1. Open the image in Photoshop.

2. If the image has more than one layer, flatten the image.

3. Check that the image is 8-bit. If it is 16-bit, change it to 8-bit (using Image>Mode). Later you will be saving the image in JPEG format and you cannot save a 16-bit JPEG file (no such thing exists).

4. Change the image to the sRGB colour space if it is not already in that colour space (using Edit>Convert To Profile).

5. Open the Image Size dialogue box (using Image>Image Size).

6. Put a check the “Resample Image” and “Constrain Proportions” boxes. Ignore the “Scale Style” option - you are working with a flattened image that has no layers with styles.

7. Select either “Bicubic” or “Bicubic Sharper” as the interpolation method. "Bicubic" gives the smoothest tonal changes; "Bicubic Sharper" produces a sharper image.

8. Change the “Pixel Dimensions” so that EITHER the width is 1024 pixels (for a landscape image) or the height is 768 pixels (for a portrait image). The other dimension will change automatically because you have the "Constrain Proportions" option checked. NOTE: Check that both dimensions are within the required limits (1024 x 768 pixels when the image is viewed in its correct orientation).

9. Do not change anything in the “Document Size” section of the dialogue box – this is only used when you are going to print the image. It does not matter what value is in the "Resolution" box - this will make no difference to the appearance of the image on a computer screen or when it is projected with a data projector. [Refer to this tutorial if you want a more detailed explanation.]

10. Click “OK”.

11. To save the image – select File>Save As.

12. When the "Save As" dialogue box appears, name the file using whatever style of naming is required and select the directory/folder where you want to save it.

13. Select JPEG as the “Format” and click “Save”.

14. In the “JPEG Options” dialogue box set the “Quality” to “12” and check the file size – on a Windows machine this will be in the “Size” section of the dialogue box (near the bottom). The size information will look something like ~645.32K/206s@56Kbps - the file size is the first bit “645.32K” in this example – just ignore the information after the “/”. On a Macintosh computer the size is written just below the word “Preview”.

15. If the file size is greater than 300 KB (or whatever other maximum size you are trying to achieve) then change the “Quality” number from “12” to “11” and check the size again. Keep reducing the quality until the file size is below 300 KB (or whatever maximum file size you are trying to achieve).

16. Click “OK”. The file will be saved. Check the size of the saved file because sometimes the size shown in the Photoshop Image Size dialogue box is not particularly accurate.

     

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