To resize an image or picture we can use a freeware program IrfanView, it can be downloaded from the official site, see the Download section, there are 32 and 64 bit versions of the program.
Install the program, then start it. Now open an image or picture file to be resized. To do this, use Drag and Drop (or press the key "O" on the keyboard) to open the File Open dialog box (see Fig. 1.), or use the main menu of the program (File --> Open...).
Select a file and open it. Then press "Ctrl+R" to open Resize - Resample dialog (see fig. 2). This dialog also can be open from the main menu "Image --> Resize/Resample...".
Fig. 2. Resize/Resample dialog box in IrfanView
Let's explain this "Resize/Resample image" dialog box (Fig. 2). The "Size method" (1) is used to select a method used to resize an image - you can use "Resample (better quality)" and the filter "Lanczos" for the best quality. Also you can use other filters, for example, "Hermite filter" or "Triangle", this filters provide an alternative quality of the picture. Different filters have different features, so the more appropriate filter can be found only by an experimental way. Anyways, the difference in results will be very small.
Use the "Set new size" (4) and "Set new size as percentage of original" (3) to set a new dimension of the image. You can use pixels, centimeters, inches or percents for the new image. Note the "Preserve aspect ratio" checkbox in the field (2), it is related to (3) and (4) fields. If this checkbox is checked, any changes to the width of the image will be made proportionally to the height of the image.
The field "Some standard dimensions (pixels)" (5) provides some presets for the new image size, just like 640x480, 800x600, 1024x768 and so on. Also the image can be resized to fit the desktop. Two buttons, "Half" and "Double" provide resizing in/resizing out in two times per click.
You can see the current and new sizes of the image in the panel (6). To make the new size valid, press the button "OK" on the bottom of the "Resize/Resample image" dialog box. Now you have to save the file on the disk (use "Ctrl+S").
How to resize an image using settings described above? Let's see an example where we will resize a photo, making it two times smaller. Start the program, open the file you want to resize (press the key "O"), then press "Ctrl+R" to open the "Resize/Resample image" dialog box. Now click the button "Half" one time. If you click this button twice, the photo will be resized in four times, and so on. Press the button "OK" to close this dialog box. Now in the main screen of the program the size of the photo is two times less than the original size. Next we have to save the resized picture to the hard drive - press "Ctrl+S" to open the "Save" dialog box (see Fig. 3). Select there the file type you want to save the picture as ("Save as type") and a directory to save the file in.
Fig. 3. The File Save dialog box.
The program "IrfanView" allows to save images using different graphic formats such as gif, jpg, png, bmp, ico, raw, tiff and a lot of others. For the jpg or gif formats, there is an additional options. Check the "Show option dialog" in the "Save" dialog box to show this settings (it is on the bottom of the dialog). This allows you to change the quality of jpg files and some additional parameters for gif format. Remember, the better quality, the larger the jpg file.
How to resize several images at one time? The program "IrfanView" provides a batch file conversion. Press the "B" key (or use the main menu - select the "File --> Batch Conversion/Rename"). You'll see the "Batch Conversion" dialog box (see Fig. 4).
Fig. 4. The Batch Conversion dialog box.
Select the "Batch conversion" (1) in this dialog window, check the "Use advanced options (for bulk resize...)" on the second panel (2). It enables the button "Advanced". Select a directory to be used for saving processed files on the panel (3). Use the panel (5) to select files to be processed. Select files, then press the button "Add", so the files will be added to the panel (7). You can also Drag and Drop files to this panel from the Explorer or any other file manager.
Fig. 5. The "Set for all images" window.
Press the button "Advanced" on the panel (2) to set the new images size. It will open the window "Set for all images", check the "RESIZE" checkbox, and select a new size, as it was described above. Then press "OK" to return to the "Batch conversion" window (Fig. 4), press the button "Start Batch" (4). The renaming process starts, the processed files will be saved in the output directory (Fig. 4) shown in the panel (3).
Let's resume. To resize an image using the program "IrfanView", it takes next steps:
To use batch image resizing, use this steps:
And at the end, there are some online services that may resize images, but they are not so suitable as the program "IrfanView", they can't handle large files, and they are work very slow.