First, the "size" of your image is absolutely NOT measured in kilobytes. This is only the size of the file, which depends largely on the degree of compression chosen. Due to the JPG quality factor selected, large JPG files are of better quality and smaller, lower quality JPG files (a lower quality is not usually the best choice), but the size of the JPG files is smaller. pixel image remains unchanged.
This first part deals only with this confusion, but the answer is in the next part below.
All JPG files have a standard 24-bit color, which means the file size. image data is 3 bytes per pixel. But the size of the image is the number of pixels, for example, let's say size of the image is 4000 x 3000 pixels, 12 megapixels, so the uncompressed data size (data size when open in computer memory) is 12 x 3 = 36 million bytes. However, the data (in the JPG file) is still compressed to some extent (controlled by the JPG Quality option). As a result, the actual size of the compressed file can generally be between 1/4 and 1/12. But this example of image size remains the 4000×3000 pixels, regardless of the size of the compressed file.
300 dpi printing is for printing on paper, 300 dpi is 300 pixels per inch of printing paper. Therefore, if you set a print resolution (of this example, the image size 4000 x 3000 pixels) to 300 dpi, it means that the print will be 4000/300 x 3000/300 = 13.3 x 10 inches on paper. This specific print size is simply due to the fact that the size of the image is 4000×3000 pixels, which corresponds to the stretch of 300 pixels per inch when printing on the paper.
uncompressed data size: 36 million bytes
JPG Compressed Data File Size: Maybe 9 to 3 million bytes.
print size at 300dpi: 13.3 x 12 inches
image size: 4000 x 3000 pixels.
Each of these concerns have different units.
Whoever asked you 300 dp should have specified the size printed in inches that he was looking for. Otherwise, 300 has no meaning or use for them. Dpi has nothing to do with the size of the image, which is in pixels. Dpi affects the print size, but the size of the image in pixels must be known.
The applicant probably implies that he wants a large image, probably the size of the original image of the camera in pixels. This means that they must have asked for the size of the image in pixels, or at least the size printed in inches if the resolution is 300 dpi.
The terms dpi and ppi used in printing are interchangeable in the same direction, pixels per inch. More can be said about this, but it is not important today because printer drivers have abandoned the idea of asking questions about print quality in "ink drops per inch" , which is quite different. To avoid this, the quality of printing today belongs to the categories Good, Best and Best.
With the help of a photo editor, you can simply change the number of dpi so that it is 300dpi. This is called "resize the printed size" in inches, that's what the dpi does. This will then specify a specific print size in inches, which may be acceptable or not, depending on the size of your image in pixels and your purpose of using the image.
Yes, if you set a resolution of 300 dpi and save the file, the number will be 300 dpi. Today, some publishers can call it 300 dpi, it is the same thing.
This scaling at 300 dpi does NOT affect the number of bytes, unless you also change the resampled size in pixels or the JPG quality factor.
This changes the size of the resized print in inches, which is the number of inches that 300 pixels per inch will print from the pixels you have.