Batch resize images using Faststone image viewer

For what is essentially an image viewing application Faststone image viewer has a surprising number of useful editing features. One of it’s most powerful features is the batch convert feature. Batch convert gives you a lot of options like resize, crop, compress, rotate, color adjustments, add watermark etc. Let’s take a look at the resize option. Even if you are a not going to do any batch processing, the Batch Resize option of FastStone is well worth a look since it has a lot more resizing options than it’s dedicated single image resize.

First, select the images you want to resize, then choose batch convert selected images option from the tools menu.
FastStone Tools menu with Batch Convert Selected Images option highlightedThis opens up the batch-convert window.
batch convert windowHere you can add files to your selection or remove files from your selection. Next, make sure that the tick box next to Use Advanced option is ticked. This would make the Advanced options button visible, click on it to open the advanced options window.
Advanced options windowMake sure that the tick box before resize is ticked, that would make the resize options visible.

In the In Pixels section, you can specify the height and width of the new image in pixels. The In Print Size section is quite similar to In Pixels section except that here you specify the image size in inches or centimeters. Both sections have many common options, let us take a look at some of them. If the new image resolution you want has the same aspect ratio as the old image then you don’t need to bother with most of these options.

If the aspect ratio is different then things are more difficult. If you disable the Preserve Aspect Ratio option you will get a squished looking image as shown below.

Original image 400 x 300 resolution image
Original 400 x 300 resolution image
Image resized to 300 x 300 with preserve aspect ratio off
Resized to 300 x 300 with preserve aspect ratio off


If you reenable Preserve Aspect Ratio option and choose smart-crop, Faststone will automatically crop the image if the new aspect ratio does not match the aspect ratio of the original image. If there is no aspect ratio mismatch FastStone will just resizes the image. For example, if you resize the original 400 x 300 image to 200 x 150 resolution with smart-crop enabled, the image gets simply resized and no cropping is done. Conversely, if either height or width of the new image matches the corresponding height or width of the original image no resizing is done and the image is simply cropped to fix any aspect ratio mismatch. The result of such a smart- crop on our original image is shown below.

image resized to 300 x 300 with smart-crop enabled
resized to 300 x 300 with smart-crop enabled

If there is a mismatch in both of the dimensions and in the aspect ratio then both cropping and resizing is done.


Smart-fill automatically adds bars on the edge of the image to manage aspect ratio mismatches without having to squish the image.

image resized to 300 x 300 with smart-fill on, you can see black borders around the image
resized to 300 x 300 with smart-fill on

In this example, I did the same 400 x 300 to 300 x 300 resize, this time with smart-fill enabled instead of smart-crop. Instead of cropping from the sides to reduce the width as earlier FastStone added black borders to the top and bottom to increase the height. The user can choose the color of the fill, so I could have chosen Orange color, but when you are doing a true “batch” resize you cannot choose a different color for each image.

Preserve aspect-ratio

If the preserve aspect ratio option is enabled, without enabling any of the aspect-ratio adjusting features like smart-crop or smart-fill, the resolution of the new image might be different from what you asked for. FastStone calculates the new resolution based on three considerations. First, it makes sure that the aspect ratio of the new image matches the aspect ratio of the original image. Second, it makes sure that neither the width nor the height exceeds the width and height you have specified. Third, it makes sure that you get the largest possible image while still respecting the first and second conditions.

image resized using the plain preserve aspect ratio option
asked for 250 x 250 but got 250 x 188 instead

In the above example, I asked FastStone to resize the original 400 x 300 image to 250 x 250 but got 250 x 188 instead. Here is an explanation for this behavior. The width which I asked for was disproportionately smaller compared to the height. Since the requested width was already small, FastStone could not reduce it further and still make sure that the new image is the largest possible. It could not increase the width since it is trying to make sure that the dimensions of the new image do not exceed the user requested dimensions. So it kept the requested width unchanged and reduced the requested height to make the aspect ratios match and thus arrived at 250 x 188 as the target resolution. As you can see, while the preserve aspect-ratio option might seem to give inaccurate results at first glance it is actually a useful feature if you want the largest possible image below a certain size threshold.

Resize based on one side

In the previous section, we looked at how to get the largest possible image while keeping both it’s height and width below a specific threshold. But what if you are interested in only one of the dimensions. For example, if you are looking for images for the side-bar of a webpage, you would probably want the width to be some pre-determined size but could be less concerned about getting an exact height. The Preserve Aspect Ratio option described in the previous section can be used to achieve this, but it would require you to do some basic resolution and aspect-ratio calculations. FastStone actually has a dedicated option for this type of resizing.

Click the Resize based on one side radio-button to activate the related options.
Resize window with Resize based on one side radio-button activatedChoose which of the dimensions must be fixed and specify the number of pixels it must measure. There is also an option to pre-set the number of pixels on the long side or the short side, whichever side that may happen to be.

Resize in percentage

There is also an option to specify how much you want to resize as a percentage. Click on the In Percentage radio button to choose this option.
Resize window with In Percentage radio-button activatedThere are not many options here just type in the percentage you want or choose one of the presets.

1 thought on “Batch resize images using Faststone image viewer”

  1. Dzięki za pomoc, w końcu nie muszę edytować pojedynczo:)
    ENG: Thanks for the help. finally I don’t have to edit one by one 🙂

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